How memory works

Visual Memory

Older news items (pre-2010) brought over from the old website

More light shed on distinction between long and short-term memory

The once clear-cut distinction between long- and short-term memory has increasingly come under fire in recent years. A new study involving patients with a specific form of epilepsy called 'temporal lobe epilepsy with bilateral hippocampal sclerosis' has now clarified the distinction. The patients, who all had severely compromised hippocampi, were asked to try and memorize photographic images depicting normal scenes. Their memory was tested and brain activity recorded after five seconds or 60 minutes. As expected, the patients could not remember the images after 60 minutes, but could distinguish seen-before images from new at five seconds. However, their memory was poor when asked to recall details about the images. Brain activity showed that short-term memory for details required the coordinated activity of a network of visual and temporal brain areas, whereas standard short-term memory drew on a different network, involving frontal and parietal regions, and independent of the hippocampus.

[996] Cashdollar, N., Malecki U., Rugg-Gunn F. J., Duncan J. S., Lavie N., & Duzel E.
(2009).  Hippocampus-dependent and -independent theta-networks of active maintenance.
Proceedings of the National Academy of Sciences. 106(48), 20493 - 20498.

http://www.eurekalert.org/pub_releases/2009-11/ucl-tal110909.php

Individual differences in working memory capacity depend on two factors

A new computer model adds to our understanding of working memory, by showing that working memory can be increased by the action of the prefrontal cortex in reinforcing activity in the parietal cortex (where the information is temporarily stored). The idea is that the prefrontal cortex sends out a brief stimulus to the parietal cortex that generates a reverberating activation in a small subpopulation of neurons, while inhibitory interactions with neurons further away prevents activation of the entire network. This lateral inhibition is also responsible for limiting the mnemonic capacity of the parietal network (i.e. provides the limit on your working memory capacity). The model has received confirmatory evidence from an imaging study involving 25 volunteers. It was found that individual differences in performance on a short-term visual memory task were correlated with the degree to which the dorsolateral prefrontal cortex was activated and its interconnection with the parietal cortex. In other words, your working memory capacity is determined by both storage capacity (in the posterior parietal cortex) and prefrontal top-down control. The findings may help in the development of ways to improve working memory capacity, particularly when working memory is damaged.

[441] Edin, F., Klingberg T., Johansson P., McNab F., Tegner J., & Compte A.
(2009).  Mechanism for top-down control of working memory capacity.
Proceedings of the National Academy of Sciences. 106(16), 6802 - 6807.

http://www.eurekalert.org/pub_releases/2009-04/i-id-aot040109.php

Some short-term memories die suddenly, no fading

We don’t remember everything; the idea of memory as being a video faithfully recording every aspect of everything we have ever experienced is a myth. Every day we look at the world and hold a lot of what we say for no more than a few seconds before discarding it as not needed any more. Until now it was thought that these fleeting visual memories faded away, gradually becoming more imprecise. Now it seems that such memories remain quite accurate as long as they exist (about 4 seconds), and then just vanish away instantly. The study involved testing memory for shapes and colors in 12 adults, and it was found that the memory for shape or color was either there or not there – the answers either correct or random guesses. The probability of remembering correctly decreased between 4 and 10 seconds.

[941] Zhang, W., & Luck S. J.
(2009).  Sudden death and gradual decay in visual working memory.
Psychological Science: A Journal of the American Psychological Society / APS. 20(4), 423 - 428.

http://www.eurekalert.org/pub_releases/2009-04/uoc--ssm042809.php

Where visual short-term memory occurs

Working memory used to be thought of as a separate ‘store’, and now tends to be regarded more as a process, a state of mind. Such a conception suggests that it may occur in the same regions of the brain as long-term memory, but in a pattern of activity that is somehow different from LTM. However, there has been little evidence for that so far. Now a new study has found that information in WM may indeed be stored via sustained, but low, activity in sensory areas. The study involved volunteers being shown an image for one second and instructed to remember either the color or the orientation of the image. After then looking at a blank screen for 10 seconds, they were shown another image and asked whether it was the identical color/orientation as the first image. Brain activity in the primary visual cortex was scanned during the 10 second delay, revealing that areas normally involved in processing color and orientation were active during that time, and that the pattern only contained the targeted information (color or orientation).

[1032] Serences, J. T., Ester E. F., Vogel E. K., & Awh E.
(2009).  Stimulus-Specific Delay Activity in Human Primary Visual Cortex.
Psychological Science. 20(2), 207 - 214.

http://www.eurekalert.org/pub_releases/2009-02/afps-sih022009.php
http://www.eurekalert.org/pub_releases/2009-02/uoo-dsm022009.php

The finding is consistent with that of another study published this month, in which participants were shown two examples of simple striped patterns at different orientations and told to hold either one or the other of the orientations in their mind while being scanned. Orientation is one of the first and most basic pieces of visual information coded and processed by the brain. Using a new decoding technique, researchers were able to predict with 80% accuracy which of the two orientations was being remembered 11 seconds after seeing a stimulus, from the activity patterns in the visual areas. This was true even when the overall level of activity in these visual areas was very weak, no different than looking at a blank screen.

[652] Harrison, S. A., & Tong F.
(2009).  Decoding reveals the contents of visual working memory in early visual areas.
Nature. 458(7238), 632 - 635.

http://www.eurekalert.org/pub_releases/2009-02/vu-edi021709.php
http://www.physorg.com/news154186809.html

Even toddlers can ‘chunk' information for better remembering

We all know it’s easier to remember a long number (say a phone number) when it’s broken into chunks. Now a study has found that we don’t need to be taught this; it appears to come naturally to us. The study showed 14 months old children could track only three hidden objects at once, in the absence of any grouping cues, demonstrating the standard limit of working memory. However, with categorical or spatial cues, the children could remember more. For example, when four toys consisted of two groups of two familiar objects, cats and cars, or when six identical orange balls were grouped in three groups of two.

[196] Feigenson, L., & Halberda J.
(2008).  From the Cover: Conceptual knowledge increases infants' memory capacity.
Proceedings of the National Academy of Sciences. 105(29), 9926 - 9930.

http://www.eurekalert.org/pub_releases/2008-07/jhu-etg071008.php

Full text available at http://www.pnas.org/content/105/29/9926.abstract?sid=c01302b6-cd8e-4072-842c-7c6fcd40706f

Working memory has a fixed number of 'slots'

A study that showed volunteers a pattern of colored squares for a tenth of a second, and then asked them to recall the color of one of the squares by clicking on a color wheel, has found that working memory acts like a high-resolution camera, retaining three or four features in high detail. Unlike a digital camera, however, it appears that you can’t increase the number of images you can store by lowering the resolution. The resolution appears to be constant for a given individual. However, individuals do differ in the resolution of each feature and the number of features that can be stored.

[278] Zhang, W., & Luck S. J.
(2008).  Discrete fixed-resolution representations in visual working memory.
Nature. 453(7192), 233 - 235.

http://www.physorg.com/news126432902.html
http://www.eurekalert.org/pub_releases/2008-04/uoc--wmh040208.php

And another study of working memory has attempted to overcome the difficulties involved in measuring a person’s working memory capacity (ensuring that no ‘chunking’ of information takes place), and concluded that people do indeed have a fixed number of ‘slots’ in their working memory. In the study, participants were shown two, five or eight small, scattered, different-colored squares in an array, which was then replaced by an array of the same squares without the colors, after which the participant was shown a single color in one location and asked to indicate whether the color in that spot had changed from the original array.

[437] Rouder, J. N., Morey R. D., Cowan N., Zwilling C. E., Morey C. C., & Pratte M. S.
(2008).  An assessment of fixed-capacity models of visual working memory.
Proceedings of the National Academy of Sciences. 105(16), 5975 - 5979.

http://www.eurekalert.org/pub_releases/2008-04/uom-mpd042308.php

Impressive feats in visual memory

In light of all the recent experiments emphasizing how small our short-term visual memory is, it’s comforting to be reminded that, nevertheless, we have an amazing memory for pictures — in the right circumstances. Those circumstances include looking at images of familiar objects, as opposed to abstract artworks, and being motivated to do well (the best-scoring participant was given a cash prize). In the study, 14 people aged 18 to 40 viewed 2,500 images, one at a time, for a few seconds. Afterwards, they were shown pairs of images and asked to select the exact image they had seen earlier. The previously viewed item could be paired with either an object from a novel category, an object of the same basic-level category, or the same object in a different state or pose. Stunningly, participants on average chose the correct image 92%, 88% and 87% of the time, in each of the three pairing categories respectively.

[870] Brady, T. F., Konkle T., Alvarez G. A., & Oliva A.
(2008).  Visual long-term memory has a massive storage capacity for object details.
Proceedings of the National Academy of Sciences. 105(38), 14325 - 14329.

Full text available at http://www.pnas.org/content/105/38/14325.abstract

Attention grabbers snatch lion's share of visual memory

It’s long been thought that when we look at a visually "busy" scene, we are only able to store a very limited number of objects in our visual short-term or working memory. For some time, this figure was believed to be four or five objects, but a recent report suggested it could be as low as two. However, a new study reveals that although it might not be large, it’s more flexible than we thought. Rather than being restricted to a limited number of objects, it can be shared out across the whole image, with more memory allocated for objects of interest and less for background detail. What’s of interest might be something we’ve previously decided on (i.e., we’re searching for), or something that grabs our attention.  Eye movements also reveal how brief our visual memory is, and that what our eyes are looking at isn’t necessarily what we’re ‘seeing’ — when people were asked to look at objects in a particular sequence, but the final object disappeared before their eyes moved on to it, it was found that the observers could more accurately recall the location of the object that they were about to look at than the one that they had just been looking at.

[1398] Bays, P. M., & Husain M.
(2008).  Dynamic shifts of limited working memory resources in human vision.
Science (New York, N.Y.). 321(5890), 851 - 854.

http://www.physorg.com/news137337380.html

More on how short-term memory works

It’s been established that visual working memory is severely limited — that, on average, we can only be aware of about four objects at one time. A new study explored the idea that this capacity might be affected by complexity, that is, that we can think about fewer complex objects than simple objects. It found that complexity did not affect memory capacity. It also found that some people have clearer memories of the objects than other people, and that this is not related to how many items they can remember. That is, a high IQ is associated with the ability to hold more items in working memory, but not with the clarity of those items.

[426] Awh, E., Barton B., & Vogel E. K.
(2007).  Visual working memory represents a fixed number of items regardless of complexity.
Psychological Science: A Journal of the American Psychological Society / APS. 18(7), 622 - 628.

http://www.eurekalert.org/pub_releases/2007-07/uoo-htb071107.php
http://www.physorg.com/news103472118.html

Support for labeling as an aid to memory

A study involving an amnesia-inducing drug has shed light on how we form new memories. Participants in the study participants viewed words, photographs of faces and landscapes, and abstract pictures one at a time on a computer screen. Twenty minutes later, they were shown the words and images again, one at a time. Half of the images they had seen earlier, and half were new. They were then asked whether they recognized each one. For one session they were given midazolam, a drug used to relieve anxiety during surgical procedures that also causes short-term anterograde amnesia, and for one session they were given a placebo.
It was found that the participants' memory while in the placebo condition was best for words, but the worst for abstract images. Midazolam impaired the recognition of words the most, impaired memory for the photos less, and impaired recognition of abstract pictures hardly at all. The finding reinforces the idea that the ability to recollect depends on the ability to link the stimulus to a context, and that unitization increases the chances of this linking occurring. While the words were very concrete and therefore easy to link to the experimental context, the photographs were of unknown people and unknown places and thus hard to distinctively label. The abstract images were also unfamiliar and not unitized into something that could be described with a single word.

[1216] Reder, L. M., Oates J. M., Thornton E. R., Quinlan J. J., Kaufer A., & Sauer J.
(2006).  Drug-Induced Amnesia Hurts Recognition, but Only for Memories That Can Be Unitized.
Psychological science : a journal of the American Psychological Society / APS. 17(7), 562 - 567.

http://www.sciencedaily.com/releases/2006/07/060719092800.htm

Discovery disproves simple concept of memory as 'storage space'

The idea of memory “capacity” has become more and more eroded over the years, and now a new technique for measuring brainwaves seems to finally knock the idea on the head. Consistent with recent research suggesting that a crucial problem with aging is a growing inability to ignore distracting information, this new study shows that visual working memory depends on your ability to filter out irrelevant information. Individuals have long been characterized as having a “high” working memory capacity or a “low” one — the assumption has been that these people differ in their storage capacity. Now it seems it’s all about a neural mechanism that controls what information gets into awareness. People with high capacity have a much better ability to ignore irrelevant information.

[1091] Vogel, E. K., McCollough A. W., & Machizawa M. G.
(2005).  Neural measures reveal individual differences in controlling access to working memory.
Nature. 438(7067), 500 - 503.

http://www.eurekalert.org/pub_releases/2005-11/uoo-dds111805.php

Language cues help visual learning in children

A study of 4-year-old children has found that language, in the form of specific kinds of sentences spoken aloud, helped them remember mirror image visual patterns. The children were shown cards bearing red and green vertical, horizontal and diagonal patterns that were mirror images of one another. When asked to choose the card that matched the one previously seen, the children tended to mistake the original card for its mirror image, showing how difficult it was for them to remember both color and location. However, if they were told, when viewing the original card, a mnemonic cue such as ‘The red part is on the left’, they performed “reliably better”.

The paper was presented by a graduate student at the 17th annual meeting of the American Psychological Society, held May 26-29 in Los Angeles.

http://www.eurekalert.org/pub_releases/2005-05/jhu-lc051705.php

An advantage of age

A study comparing the ability of young and older adults to indicate which direction a set of bars moved across a computer screen has found that although younger participants were faster when the bars were small or low in contrast, when the bars were large and high in contrast, the older people were faster. The results suggest that the ability of one neuron to inhibit another is reduced as we age (inhibition helps us find objects within clutter, but makes it hard to see the clutter itself). The loss of inhibition as we age has previously been seen in connection with cognition and speech studies, and is reflected in our greater inability to tune out distraction as we age. Now we see the same process in vision.

[1356] Betts, L. R., Taylor C. P., Sekuler A. B., & Bennett P. J.
(2005).  Aging Reduces Center-Surround Antagonism in Visual Motion Processing.
Neuron. 45(3), 361 - 366.

http://psychology.plebius.org/article.htm?article=739
http://www.eurekalert.org/pub_releases/2005-02/mu-opg020305.php

Why working memory capacity is so limited

There’s an old parlor game whereby someone brings into a room a tray covered with a number of different small objects, which they show to the people in the room for one minute, before whisking it away again. The participants are then required to write down as many objects as they can remember. For those who perform badly at this type of thing, some consolation from researchers: it’s not (entirely) your fault. We do actually have a very limited storage capacity for visual short-term memory.
Now visual short-term memory is of course vital for a number of functions, and reflecting this, there is an extensive network of brain structures supporting this type of memory. However, a new imaging study suggests that the limited storage capacity is due mainly to just one of these regions: the posterior parietal cortex. An interesting distinction can be made here between registering information and actually “holding it in mind”. Activity in the posterior parietal cortex strongly correlated with the number of objects the subjects were able to remember, but only if the participants were asked to remember. In contrast, regions of the visual cortex in the occipital lobe responded differently to the number of objects even when participants were not asked to remember what they had seen.

[598] Todd, J. J., & Marois R.
(2004).  Capacity limit of visual short-term memory in human posterior parietal cortex.
Nature. 428(6984), 751 - 754.

http://www.eurekalert.org/pub_releases/2004-04/vu-slo040704.php
http://tinyurl.com/2jzwe (Telegraph article)

Brain signal predicts working memory capacity

Our visual short-term memory may have an extremely limited capacity, but some people do have a greater capacity than others. A new study reveals that an individual's capacity for such visual working memory can be predicted by his or her brainwaves. In the study, participants briefly viewed a picture containing colored squares, followed by a one-second delay, and then a test picture. They pressed buttons to indicate whether the test picture was identical to -- or differed by one color -- from the one seen earlier. The more squares a subject could correctly identify having just seen, the greater his/her visual working memory capacity, and the higher the spike of corresponding brain activity – up to a point. Neural activity of subjects with poorer working memory scores leveled off early, showing little or no increase when the number of squares to remember increased from 2 to 4, while those with high capacity showed large increases. Subjects averaged 2.8 squares.

[1154] Vogel, E. K., & Machizawa M. G.
(2004).  Neural activity predicts individual differences in visual working memory capacity.
Nature. 428(6984), 748 - 751.

http://www.eurekalert.org/pub_releases/2004-04/niom-bsp041604.php

Learning without desire or awareness

We have long known that learning can occur without attention. A recent study demonstrates learning that occurs without attention, without awareness and without any task relevance. Subjects were repeatedly presented with a background motion signal so weak that its direction was not visible; the invisible motion was an irrelevant background to the central task that engaged the subject's attention. Despite being below the threshold of visibility and being irrelevant to the central task, the repetitive exposure improved performance specifically for the direction of the exposed motion when tested in a subsequent suprathreshold test. These results suggest that a frequently presented feature sensitizes the visual system merely owing to its frequency, not its relevance or salience.

[594] Watanabe, T., Nanez J. E., & Sasaki Y.
(2001).  Perceptual learning without perception.
Nature. 413(6858), 844 - 848.

http://www.nature.com/nsu/011025/011025-12.html
http://tinyurl.com/ix98

Visual memory better than previously thought

Why is it that you can park your car at a huge mall and find it a few hours later without much problem, or make your way through a store you have never been to before? The answer may lie in our ability to build up visual memories of a scene in a short period of time. A new study counters current thinking that visual memory is generally poor and that people quickly forget the details of what they have seen. It appears that even with very limited visual exposure to a scene, people are able to build up strong visual memories and, in fact, their recall of objects in the scene improved with each exposure. It is suggested these images aren't stored in short-term or long-term memory, but in medium-term memory, which lasts for a few minutes and appears to be specific to visual information as opposed to verbal or semantic information. "Medium-term memory depends on the visual context of the scene, such as the background, furniture and walls, which seems to be key in the ability to keep in mind the location and identity of objects. These disposable accumulated visual memories can be recalled in a few minutes if faced with that scene again, but are discarded in a day or two if the scene is not viewed again so they don't take up valuable memory space."

Melcher, D. 2001. Persistence of visual memory for scenes. Nature, 412 (6845), 401.

http://www.eurekalert.org/pub_releases/2001-07/rtsu-rrf072501.php

tags memworks: 

Attention

See separate pages for

Attention problems

Attention training

Older news items (pre-2010) brought over from the old website

Attention is more about reducing the noticeability of the unattended

No visual scene can be processed in one fell swoop — we piece it together from the bits we pay attention to (which explains why we sometimes miss objects completely, and can’t understood how we could have missed them when we finally notice them). We know that paying attention to something increases the firing rate of neurons tuned for that type of stimulus, and until a recent study we thought that was the main process underlying our improved perception when we focus on something. However a macaque study has found that the main cause — perhaps four times as important — is a reduction in the background noise, allowing the information coming in to be much more noticeable.

[1093] Mitchell, J. F., Sundberg K. A., & Reynolds J. H.
(2009).  Spatial Attention Decorrelates Intrinsic Activity Fluctuations in Macaque Area V4.
Neuron. 63(6), 879 - 888.

http://esciencenews.com/articles/2009/09/23/rising.above.din

Brainwaves regulate our searching

A long-standing question concerns how we search complex visual scenes. For example, when you enter a crowded room, how do you go about searching for your friends? Now a monkey study reveals that visual attention jumps sequentially from point to point, shifting focus around 25 times in a second. Intriguingly, and unexpectedly, it seems this timing is determined by brainwaves. The finding connects speed of thinking with the oscillation frequency of brainwaves, giving a new significance to brainwaves (whose function is rather mysterious, but of increasing interest to researchers), and also suggesting an innovative approach to improving attention.

[1118] Buschman, T. J., & Miller E. K.
(2009).  Serial, Covert Shifts of Attention during Visual Search Are Reflected by the Frontal Eye Fields and Correlated with Population Oscillations.
Neuron. 63(3), 386 - 396.

http://www.eurekalert.org/pub_releases/2009-08/miot-tme080609.php

Ability to ignore distraction most important for attention

Confirming an earlier study, a series of four experiments involving 84 students has found that students with high working memory capacity were noticeably better able to ignore distractions and stay focused on their tasks. The findings provide more evidence that the poor attentional capacity of individuals with low working memory capacity result from a reduced ability to ignore attentional capture (stimuli that involuntarily “capture” your attention, like a loud noise or a suddenly appearing object), rather than an inability to focus.

[828] Fukuda, K., & Vogel E. K.
(2009).  Human Variation in Overriding Attentional Capture.
J. Neurosci.. 29(27), 8726 - 8733.

http://www.eurekalert.org/pub_releases/2009-08/uoo-bbo080609.php

Stress disrupts task-switching, but the brain can bounce back

A new neuroimaging study involving 20 male M.D. candidates in the middle of preparing for their board exams has found that they had a harder time shifting their attention from one task to another after a month of stress than other healthy young men who were not under stress. The finding replicates what has been found in rat studies, and similarly correlates with impaired function in an area of the prefrontal cortex that is involved in attention. However, the brains recovered their function within a month of the end of the stressful period.

[829] Liston, C., McEwen B. S., & Casey B. J.
(2009).  Psychosocial stress reversibly disrupts prefrontal processing and attentional control.
Proceedings of the National Academy of Sciences. 106(3), 912 - 917.

Full text available at http://www.pnas.org/content/106/3/912.abstract
http://www.eurekalert.org/pub_releases/2009-01/ru-sdh012709.php

Attention, it’s all about connecting

An imaging study in which volunteers spent an hour identifying letters that flashed on a screen has shed light on what happens when our attention wanders. Reduced communication in the ventral fronto-parietal network, critical for attention, was found to predict slower response times 5-8 seconds before the letters were presented.

Daniel Weissman presented the results at the 38th annual meeting of the Society for Neuroscience, held Nov. 15 to 19 in Washington, DC.

http://www.newscientist.com/article/mg20026865.600-bored-your-brain-is-disconnecting.html

The importance of acetylcholine

A rat study suggests that acetylcholine, a neurotransmitter known to be important for attention, is critical for "feature binding"— the process by which our brain combines all of the specific features of an object and gives us a complete and unified picture of it. The findings may lead to improved therapies and treatments for a variety of attention and memory disorders.

[1265] Botly, L. C. P. [1], & De Rosa E.
(2008).  A Cross-Species Investigation of Acetylcholine, Attention, and Feature Binding.
Psychological Science. 19, 1185 - 1193.

http://www.eurekalert.org/pub_releases/2008-11/afps-bba111808.php

Attention grabbers snatch lion's share of visual memory

It’s long been thought that when we look at a visually "busy" scene, we are only able to store a very limited number of objects in our visual short-term or working memory. For some time, this figure was believed to be four or five objects, but a recent report suggested it could be as low as two. However, a new study reveals that although it might not be large, it’s more flexible than we thought. Rather than being restricted to a limited number of objects, it can be shared out across the whole image, with more memory allocated for objects of interest and less for background detail. What’s of interest might be something we’ve previously decided on (i.e., we’re searching for), or something that grabs our attention.  Eye movements also reveal how brief our visual memory is, and that what our eyes are looking at isn’t necessarily what we’re ‘seeing’ — when people were asked to look at objects in a particular sequence, but the final object disappeared before their eyes moved on to it, it was found that the observers could more accurately recall the location of the object that they were about to look at than the one that they had just been looking at.

[1398] Bays, P. M., & Husain M.
(2008).  Dynamic shifts of limited working memory resources in human vision.
Science (New York, N.Y.). 321(5890), 851 - 854.

http://www.physorg.com/news137337380.html

How Ritalin works to focus attention

Ritalin has been widely used for decades to treat attention deficit hyperactivity disorder (ADHD), but until now the mechanism of how it works hasn’t been well understood. Now a rat study has found that Ritalin, in low doses, fine-tunes the functioning of neurons in the prefrontal cortex, and has little effect elsewhere in the brain. It appears that Ritalin dramatically increases the sensitivity of neurons in the prefrontal cortex to signals coming from the hippocampus. However, in higher doses, PFC neurons stopped responding to incoming information, impairing cognition. Low doses also reinforced coordinated activity of neurons, and weakened activity that wasn't well coordinated. All of this suggests that Ritalin strengthens dominant and important signals within the PFC, while lessening weaker signals that may act as distractors.

[663] Devilbiss, D. M., & Berridge C. W.
(2008).  Cognition-Enhancing Doses of Methylphenidate Preferentially Increase Prefrontal Cortex Neuronal Responsiveness.
Biological Psychiatry. 64(7), 626 - 635.

http://www.eurekalert.org/pub_releases/2008-06/uow-suh062408.php

Disentangling attention

A new study provides more evidence that the ability to deliberately focus your attention is physically separate in the brain from the part that helps you filter out distraction. The study trained monkeys to take attention tests on a video screen in return for a treat of apple juice. When the monkeys voluntarily concentrated (‘top-down’ attention), the prefrontal cortex was active, but when something distracting grabbed their attention (‘bottom-up’ attention), the parietal cortex became active. The electrical activity in these two areas vibrated in synchrony as they signaled each other, but top-down attention involved synchrony that was stronger in the lower-frequencies and bottom-up attention involved higher frequencies. These findings may help us develop treatments for attention disorders.

[1071] Buschman, T. J., & Miller E. K.
(2007).  Top-Down Versus Bottom-Up Control of Attention in the Prefrontal and Posterior Parietal Cortices.
Science. 315(5820), 1860 - 1862.

http://dsc.discovery.com/news/2007/03/29/attention_hea.html?category=health

Asymmetrical brains let fish multitask

A fish study provides support for a theory that lateralized brains allow animals to better handle multiple activities, explaining why vertebrate brains evolved to function asymmetrically. The minnow study found that nonlateralized minnows were as good as those bred to be lateralized (enabling it to favor one or other eye) at catching shrimp. However, when the minnows also had to look out for a sunfish (a minnow predator), the nonlateralized minnows took nearly twice as long to catch 10 shrimp as the lateralized fish.

[737] Dadda, M., & Bisazza A.
(2006).  Does brain asymmetry allow efficient performance of simultaneous tasks?.
Animal Behaviour. 72(3), 523 - 529.

http://sciencenow.sciencemag.org/cgi/content/full/2006/623/2?etoc

Why are uniforms uniform? Because color helps us track objects

Laboratory tests have revealed that humans can pay attention to only 3 objects at a time. Yet there are instances in the real world — for example, in watching a soccer match — when we certainly think we are paying attention to more than 3 objects. Are we wrong? No. Anew study shows how we do it — it’s all in the color coding. People can focus on more than three items at a time if those items share a common color. But, logically enough, no more than 3 color sets.

[927] Halberda, J., Sires S. F., & Feigenson L.
(2006).  Multiple spatially overlapping sets can be enumerated in parallel.
Psychological Science: A Journal of the American Psychological Society / APS. 17(7), 572 - 576.

http://www.eurekalert.org/pub_releases/2006-06/jhu-wau062106.php

An advantage of age

A study comparing the ability of young and older adults to indicate which direction a set of bars moved across a computer screen has found that although younger participants were faster when the bars were small or low in contrast, when the bars were large and high in contrast, the older people were faster. The results suggest that the ability of one neuron to inhibit another is reduced as we age (inhibition helps us find objects within clutter, but makes it hard to see the clutter itself). The loss of inhibition as we age has previously been seen in connection with cognition and speech studies, and is reflected in our greater inability to tune out distraction as we age. Now we see the same process in vision.

[1356] Betts, L. R., Taylor C. P., Sekuler A. B., & Bennett P. J.
(2005).  Aging Reduces Center-Surround Antagonism in Visual Motion Processing.
Neuron. 45(3), 361 - 366.

http://psychology.plebius.org/article.htm?article=739
http://www.eurekalert.org/pub_releases/2005-02/mu-opg020305.php

We weren't made to multitask

A new imaging study supports the view that we can’t perform two tasks at once, rather, the tasks must wait their turn — queuing up for their turn at processing.

[1070] Jiang, Y., Saxe R., & Kanwisher N.
(2004).  Functional magnetic resonance imaging provides new constraints on theories of the psychological refractory period.
Psychological Science: A Journal of the American Psychological Society / APS. 15(6), 390 - 396.

http://www.eurekalert.org/pub_releases/2004-06/aps-wwm060704.php

More light shed on memory encoding

Anything we perceive contains a huge amount of sensory information. How do we decide what bits to process? New research has identified brain cells that streamline and simplify sensory information, markedly reducing the brain's workload. The study found that when monkeys were taught to remember clip art pictures, their brains reduced the level of detail by sorting the pictures into categories for recall, such as images that contained "people," "buildings," "flowers," and "animals." The categorizing cells were found in the hippocampus. As humans do, different monkeys categorized items in different ways, selecting different aspects of the same stimulus image, most likely reflecting different histories, strategies, and expectations residing within individual hippocampal networks.

[662] Hampson, R. E., Pons T. P., Stanford T. R., & Deadwyler S. A.
(2004).  Categorization in the monkey hippocampus: A possible mechanism for encoding information into memory.
Proceedings of the National Academy of Sciences of the United States of America. 101(9), 3184 - 3189.

http://www.eurekalert.org/pub_releases/2004-02/wfub-nfo022604.php

Neural circuits that control eye movements play crucial role in visual attention

Everyone agrees that to improve your memory it is important to “pay attention”. Unfortunately, noone really knows how to improve our ability to “pay attention”. An important step in telling us how visual attention works was recently made in a study that looked at the brain circuits that control eye movements. It appears that those brain circuits that program eye movements also govern whether the myriad signals that pour in from the locations where the eyes could move should be amplified or suppressed. It appears that the very act of preparing to move the eye to a particular location can cause an amplification (or suppression) of signals from that area. This is possible because humans and primates can attend to something without moving their eyes to that object.

[741] Moore, T., & Armstrong K. M.
(2003).  Selective gating of visual signals by microstimulation of frontal cortex.
Nature. 421(6921), 370 - 373.

http://www.eurekalert.org/pub_releases/2003-01/pu-ssh012303.php

Different aspects of attention located in different parts of the brain

We all know attention is important, but we’ve never been sure exactly what it is. Recent research suggests there’s good reason for this – attention appears to be multi-faceted, far less simple than originally conceived. Patients with specific lesions in the frontal lobes and other parts of the brain have provided evidence that different types of attentional problems are associated with injuries in different parts of the brain, suggesting that attention is not, as has been thought, a global process. The researchers have found evidence for at least three distinct processes, each located in different parts of the frontal lobes. These are: (1) a system that helps us maintain a general state of readiness to respond, in the superior medial frontal regions; (2) a system that sets our threshold for responding to an external stimulus, in the left dorsolateral region; and (3) a system that helps us selectively attend to appropriate stimuli, in the right dorsolateral region.

[260] Stuss, D. T., Binns M. A., Murphy K. J., & Alexander M. P.
(2002).  Dissociations within the anterior attentional system: effects of task complexity and irrelevant information on reaction time speed and accuracy.
Neuropsychology. 16(4), 500 - 513.

http://www.eurekalert.org/pub_releases/2002-10/apa-pda100702.php

tags memworks: 

tags problems: 

tags strategies: 

Perception

See also

Smell

Hearing

Vision

Older news items (pre-2010) brought over from the old website

Perception affected by mood

An imaging study has revealed that when people were shown a composite image with a face surrounded by "place" images, such as a house, and asked to identify the gender of the face, those in whom a bad mood had been induced didn’t process the places in the background. However, those in a good mood took in both the focal and background images. These differences in perception were coupled with differences in activity in the parahippocampal place area. Increasing the amount of information is of course not necessarily a good thing, as it may result in more distraction.

[1054] Schmitz, T. W., De Rosa E., & Anderson A. K.
(2009).  Opposing Influences of Affective State Valence on Visual Cortical Encoding.
J. Neurosci.. 29(22), 7199 - 7207.

http://www.eurekalert.org/pub_releases/2009-06/uot-pww060309.php

What we perceive is not what we sense

Perceiving a simple touch may depend as much on memory, attention, and expectation as on the stimulus itself. A study involving macaque monkeys has found that the monkeys’ perception of a touch (varied in intensity) was more closely correlated with activity in the medial premotor cortex (MPC), a region of the brain's frontal lobe known to be involved in making decisions about sensory information, than activity in the primary somatosensory cortex (which nevertheless accurately recorded the intensity of the sensation). MPC neurons began to fire before the stimulus even touched the monkeys' fingertips — presumably because the monkey was expecting the stimulus.

[263] de Lafuente, V., & Romo R.
(2005).  Neuronal correlates of subjective sensory experience.
Nat Neurosci. 8(12), 1698 - 1703.

http://www.eurekalert.org/pub_releases/2005-11/hhmi-tsi110405.php

Varied sensory experience important in childhood

A new baby has far more connections between neurons than necessary; from birth to about age 12 the brain trims 50% of these unnecessary connections while at the same time building new ones through learning and sensory stimulation — in other words, tailoring the brain to its environment. A mouse study has found that without enough sensory stimulation, infant mice lose fewer connections — indicating that connections need to be lost in order for appropriate ones to grow. The findings support the idea that parents should try to expose their children to a variety of sensory experiences.

[479] Zuo, Y., Yang G., Kwon E., & Gan W-B.
(2005).  Long-term sensory deprivation prevents dendritic spine loss in primary somatosensory cortex.
Nature. 436(7048), 261 - 265.

http://www.sciencentral.com/articles/view.htm3?article_id=218392607

Brain regions that process reality and illusion identified

Researchers have now identified the regions of the brain involved in processing what’s really going on, and what we think is going on. Macaque monkeys played a virtual reality video game in which the monkeys were tricked into thinking that they were tracing ellipses with their hands, although they actually were moving their hands in a circle. Monitoring of nerve cells revealed that the primary motor cortex represented the actual movement while the signals from cells in a neighboring area, called the ventral premotor cortex, were generating elliptical shapes. Knowing how the brain works to distinguish between action and perception will help efforts to build biomedical devices that can control artificial limbs, some day enabling the disabled to move a prosthetic arm or leg by thinking about it.

[1107] Schwartz, A. B., Moran D. W., & Reina A. G.
(2004).  Differential Representation of Perception and Action in the Frontal Cortex.
Science. 303(5656), 380 - 383.

http://news-info.wustl.edu/tips/page/normal/652.html
http://www.eurekalert.org/pub_releases/2004-02/wuis-rpb020704.php

Memory different depending on whether information received via eyes or ears

Carnegie Mellon scientists using magnetic resonance imaging found quite different brain activity patterns for reading and listening to identical sentences. During reading, the right hemisphere was not as active as expected, suggesting a difference in the nature of comprehension experienced when reading versus listening. When listening, there was greater activation in a part of Broca's area associated with verbal working memory, suggesting that there is more semantic processing and working memory storage in listening comprehension than in reading. This should not be taken as evidence that comprehension is better in one or other of these situations, merely that it is different. "Listening to an audio book leaves a different set of memories than reading does. A newscast heard on the radio is processed differently from the same words read in a newspaper."

[2540] Michael, E. B., Keller T. A., Carpenter P. A., & Just M A.
(2001).  fMRI investigation of sentence comprehension by eye and by ear: Modality fingerprints on cognitive processes.
Human Brain Mapping. 13(4), 239 - 252.

http://www.eurekalert.org/pub_releases/2001-08/cmu-tma081401.php

The chunking of our lives: the brain "sees" life in segments

We talk about "chunking" all the time in the context of memory. But the process of breaking information down into manageable bits occurs, it seems, right from perception. Magnetic resonance imaging reveals that when people watched movies of common, everyday, goal-directed activities (making the bed, doing the dishes, ironing a shirt), their brains automatically broke these continuous events into smaller segments. The study also identified a network of brain areas that is activated during the perception of boundaries between events. "The fact that changes in brain activity occurred during the passive viewing of movies indicates that this is how we normally perceive continuous events, as a series of segments rather than a dynamic flow of action."

Zacks, J.M., Braver, T.S., Sheridan, M.A., Donaldson, D.I., Snyder, A.Z., Ollinger, J.M., Buckner, R.L. & Raichle, M.E. 2001. Human brain activity time-locked to perceptual event boundaries. Nature Neuroscience, 4(6), 651-5.

http://www.eurekalert.org/pub_releases/2001-07/aaft-bp070201.php

Amygdala may be critical for allowing perception of emotionally significant events despite inattention

We choose what to pay attention to, what to remember. We give more weight to some things than others. Our perceptions and memories of events are influenced by our preconceptions, and by our moods. Researchers at Yale and New York University have recently published research indicating that the part of the brain known as the amygdala is responsible for the influence of emotion on perception. This builds on previous research showing that the amygdala is critically involved in computing the emotional significance of events. The amygdala is connected to those brain regions dealing with sensory experiences, and the theory that these connections allow the amygdala to influence early perceptual processing is supported by this research. Dr. Anderson suggests that “the amygdala appears to be critical for the emotional tuning of perceptual experience, allowing perception of emotionally significant events to occur despite inattention.”

[968] Anderson, A. K., & Phelps E. A.
(2001).  Lesions of the human amygdala impair enhanced perception of emotionally salient events.
Nature. 411(6835), 305 - 309.

http://www.eurekalert.org/pub_releases/2001-05/NYU-Infr-1605101.php

tags memworks: 

Sleep's role in cognition

Older news items (pre-2010) brought over from the old website

A midday nap markedly boosts the brain's learning capacity

Following on from research showing that pulling an all-nighter decreases the ability to cram in new facts by nearly 40%, a study involving 39 young adults has found that those given a 90-minute nap in the early afternoon, after being subjected to a rigorous learning task, did markedly better at later round of learning exercises, compared to those who remained awake throughout the day. The former group actually improved in their capacity to learn, while the latter became worse at learning. The findings reinforce the hypothesis that sleep is needed to clear the brain's short-term memory storage and make room for new information. Moreover, this refreshing of memory capacity was related to Stage 2 non-REM sleep (an intermediate stage between deep sleep and the REM dream stage).

The preliminary findings were presented February 21, at the annual meeting of the American Association of the Advancement of Science (AAAS) in San Diego, Calif.

http://www.eurekalert.org/pub_releases/2010-02/uoc--amn021110.php

Helping memory consolidation while you sleep

The role of sleep in consolidating new learning is now well-established, but now a study intriguingly reveals that you can improve that learning by playing sounds associated with the learning while you are asleep. The study involved 12 volunteers learning to associate each of 50 images with a random location on a computer screen. Each object was paired with its associated sound. Some 45 minutes after they had successfully mastered this task, each participant lay down in a quiet, darkened room. Once deeply asleep, 25 of these sounds were played. Although none of the participants noticed these sounds, performance was subsequently more accurate for those objects whose sounds had been played during sleep. The findings reveal that memory consolidation can be directed to specific memories through use of such cues. Another recent study found smells could also be used in this way.

[1056] Rudoy, J. D., Voss J. L., Westerberg C. E., & Paller K. A.
(2009).  Strengthening Individual Memories by Reactivating Them During Sleep.
Science. 326(5956), 1079 - 1079.

http://www.eurekalert.org/pub_releases/2009-11/nu-wum111209.php

Sleep helps reduce errors in memory

A study in which college students were shown lists of words and then, 12 hours later, asked to identify which words they had seen or heard earlier, found that those who trained at night and tested the following morning were less prone to falsely recognizing semantically similar words than those who trained in the morning and tested in the evening. It’s suspected that sleep may help strengthen the source of the memory, thus helping protect against false memories.

[254] Fenn, K. M., Gallo D. A., Margoliash D., Roediger H. L., & Nusbaum H. C.
(2009).  Reduced false memory after sleep.
Learning & Memory. 16(9), 509 - 513.

http://www.eurekalert.org/pub_releases/2009-09/msu-shr_1091009.php

How sleep consolidates memory

A rat study provides clear evidence that "sharp wave ripples", brainwaves that occur in the hippocampus when it is "off-line", most often during stage four sleep, are responsible for consolidating memory and transferring the learned information from the hippocampus to the neocortex, where long-term memories are stored. The study found that when these waves were eliminated during sleep, the rats were less able to remember a spatial navigation task.

[1083] Girardeau, G., Benchenane K., Wiener S. I., Buzsaki G., & Zugaro M. B.
(2009).  Selective suppression of hippocampal ripples impairs spatial memory.
Nat Neurosci. 12(10), 1222 - 1223.

http://www.eurekalert.org/pub_releases/2009-09/ru-deo091509.php

Memories practiced throughout the day, not just while sleeping

It is known that a certain amount of replaying of experiences occurs in the hippocampus immediately afterwards, but it has been thought that this is confined to the immediate past, while the replaying that occurs during sleep and is thought to be part of the memory consolidation process, ranges far more widely. Now a new rat study indicates that the replaying that occurs while the animal is awake is more extensive than thought, and more accurate than that which occurs during sleep. Data from the neurons indicated that the events being replayed (repeatedly) were from 20 to 30 minutes earlier, and involved different settings, indicating the replay wasn’t dependent on incoming sensory cues. It’s suggested that the less-accurate replays seen during sleep are more aimed at making connections, rather than consolidating the actual experience. The waking replays occurred during pauses in activity, perhaps suggesting the importance of making pauses for reflection during your day!

[933] Karlsson, M. P., & Frank L. M.
(2009).  Awake replay of remote experiences in the hippocampus.
Nature Neuroscience. 12(7), 913 - 918.

http://www.eurekalert.org/pub_releases/2009-06/uoc--mmb061109.php

Creative problem solving enhanced by REM sleep

A study investigating the role of sleep in creative problem-solving has found that those who experienced REM sleep between two tests performed significantly better on the later test compared to those who simply had a quiet rest, or those who napped but had no REM sleep. The findings support the idea that REM sleep (when dreams occur) has a role in forming new associations. It’s suggested that the process may be facilitated by changes to neurotransmitter systems (cholinergic and noradrenergic) during REM sleep.

[1326] Cai, D. J., Mednick S. A., Harrison E. M., Kanady J. C., & Mednick S. C.
(2009).  REM, not incubation, improves creativity by priming associative networks.
Proceedings of the National Academy of Sciences. 106(25), 10130 - 10134.

http://www.eurekalert.org/pub_releases/2009-06/uoc--lms060309.php

Sleep may be important in regulating emotional responses

A study involving 44 college students who were asked to remember scenes with neutral or negative objects on a neutral background has found that those who trained and tested on the scenes in the evening remembered the negative scenes better than those who were trained and tested in the morning. However, neutral objects were not better remembered, and the backgrounds associated with negative objects were more poorly remembered by this group. The pattern persisted when the students were tested four months later. The findings suggest that the sleeping brain calculates what is most important about an experience and selects only what is adaptive for consolidation and long term storage.

Payne, J.D., Kensinger, E., Wamsley, E. & Stickgold, R. 2009. Sleep Promotes Lasting Changes in Memory for Emotional Scenes. Presented on June 11 at SLEEP 2009, the 23rd Annual Meeting of the Associated Professional Sleep Societies; Abstract ID: 1244.

http://www.eurekalert.org/pub_releases/2009-06/aaos-smb060209.php

Sleep may help clear the brain for new learning

Although fruit flies may seem little like us, their response to sleep deprivation is similar, and so they are useful models for sleep effects on the human brain. In a recent study, flies genetically altered to make it easier to track individual synapses have revealed that during sleep the number of new synapses formed during earlier learning decreased. This decline didn’t happen if the flies were deprived of sleep. It’s theorized that this activity during sleep is a way of pruning the less relevant and important synapses (clearing away the junk, as it has been conceptualized). The study follows earlier fruit fly research showing that more learning resulted in longer sleep. It also supports recent rat research that found synaptic strength increases during the day, then weakens during sleep. The study also identified three genes essential to the links between learning and increased need for sleep, one of which is equivalent to a human gene known as serum response factor (SRF) and previously linked to brain plasticity.

[360] Donlea, J. M., Ramanan N., & Shaw P. J.
(2009).  Use-Dependent Plasticity in Clock Neurons Regulates Sleep Need in Drosophila.
Science. 324(5923), 105 - 108.

http://www.eurekalert.org/pub_releases/2009-04/wuso-smh033109.php
http://www.eurekalert.org/pub_releases/2009-04/uow-ssc033009.php

Sleep helps you learn complicated tasks & recover forgotten skills

A study involving 200 mostly female college students, who had little experience of video games. The students were taught to play a complicated, multisensory video game in which players must use both hands to deal with continually changing visual and auditory signals. Half were tested 12 hours after the training session, and the others 24 hours later. Some were given a night’s sleep before testing, others were tested the same day. Performance in the former dropped by half at testing, but when tested again the following morning, they showed a 10 percentage point improvement over their pre-test performance. For those given evening training, scores improved by about 7 percentage points, then went to 10 percentage points the next morning – which was maintained over the day. The findings indicate that although people may appear to forget much of their learning over the course of a day, a night’s sleep will restore it; moreover, sleep protected the memory from loss over the course of the next day. The findings confirm the role of sleep in consolidating memory for skills, and extends the research to complicated tasks.

[486] Brawn, T. P., Fenn K. M., Nusbaum H. C., & Margoliash D.
(2008).  Consolidation of sensorimotor learning during sleep.
Learning & Memory. 15(11), 815 - 819.

http://www.eurekalert.org/pub_releases/2008-11/uoc-shp111708.php

Sleep selectively preserves emotional memories

It’s now generally accepted that sleep plays an important role in consolidating procedural (skill) memories, but the position regarding other types of memory has been less clear.  A new study has found that sleep had an effect on emotional aspects of a memory. The study involved showing 88 students neutral scenes (such as a car parked on a street in front of shops) or negative scenes (a badly crashed car parked on a similar street). They were then tested for their memories of both the central objects in the pictures and the backgrounds in the scenes, either after 12 daytime hours, or 12 night-time hours, or 30 minutes after viewing the images, in either the morning or evening.  Those tested after 12 daytime hours largely forgot the entire negative scene, forgetting both the central objects and the backgrounds equally. But those tested after a night’s sleep remembered the emotional item (e.g., the smashed car) as well as those who were tested only 30 minutes later. Their memory of the neutral background was however, as bad as the daytime group. The findings are consistent with the view that the individual components of emotional memory become 'unbound' during sleep, enabling the brain to selectively preserve only that information it considers important.

[875] Payne, J. D., Stickgold R., Swanberg K., & Kensinger E. A.
(2008).  Sleep preferentially enhances memory for emotional components of scenes.
Psychological Science: A Journal of the American Psychological Society / APS. 19(8), 781 - 788.

http://www.physorg.com/news137908693.html
http://www.eurekalert.org/pub_releases/2008-08/bidm-sft081308.php

Aging impairs the 'replay' of memories during sleep

During sleep, the hippocampus repeatedly "replays" brain activity from recent experiences, in a process believed to be important for memory consolidation. A new rat study has found reduced replay activity during sleep in old compared to young rats, and rats with the least replay activity performed the worst in tests of spatial memory. The best old rats were also the ones that showed the best sleep replay. Indeed, the animals who more faithfully replayed the sequence of neural activity recorded during their earlier learning experience were the ones who performed better on the spatial memory task, regardless of age. The replay activity occurs during slow-wave sleep.

[1319] Gerrard, J. L., Burke S. N., McNaughton B. L., & Barnes C. A.
(2008).  Sequence Reactivation in the Hippocampus Is Impaired in Aged Rats.
J. Neurosci.. 28(31), 7883 - 7890.

http://www.eurekalert.org/pub_releases/2008-07/sfn-ait072408.php

A nap can help you learn

A study of 33 younger adults (average are 23) has found that a 45 minute afternoon nap (containing only non-REM sleep) improved performance on 3 different declarative memory tasks, but only when the subjects had reached a certain level of performance during training.

[672] Tucker, M. A., & Fishbein W.
(2008).  Enhancement of declarative memory performance following a daytime nap is contingent on strength of initial task acquisition.
Sleep. 31(2), 197 - 203.

http://www.eurekalert.org/pub_releases/2008-02/aaos-jss012808.php

Brain connections strengthen during waking hours, weaken during sleep

New research provides support for a much-debated theory that we need sleep to give our synapses time to rest and recover. The human brain is said to expend up to 80% of its energy on synaptic activity, constantly adding and strengthening connections in response to stimulation. The researchers have theorized that we need an ‘off-line period’, when we are not exposed to the environment, to take synapses down. The rodent study has revealed by several measures that synapses — the all-important points of connection between neurons — are very active when the animal is awake and very quiet during sleep. The researchers feel that these findings support the idea that our brain circuits get progressively stronger during wakefulness and that sleep helps to recalibrate them to a sustainable baseline. This theory is of course opposite to the currently dominant hypothesis, that during sleep synapses are hard at work replaying the information acquired during the previous waking hours, consolidating that information by becoming even stronger.

[631] Vyazovskiy, V. V., Cirelli C., Pfister-Genskow M., Faraguna U., & Tononi G.
(2008).  Molecular and electrophysiological evidence for net synaptic potentiation in wake and depression in sleep.
Nat Neurosci. 11(2), 200 - 208.

http://www.physorg.com/news120059987.html

Sleep reinforces the temporal sequence in memory

Following on from research showing long-term memory is consolidated during sleep through the replaying of recently encoded experiences, a study has found that the particular order in which they were experienced is also strengthened, probably by a replay of the experiences in "forward" direction. The study involved students being asked to learn triplets of words presented one after the other. Those whose recall of the order of the words was tested after sleep showed better recall, but only when they were asked to reproduce the learned words in forward direction.

[368] Drosopoulos, S., Windau E., Wagner U., & Born J.
(2007).  Sleep Enforces the Temporal Order in Memory.
PLoS ONE. 2(4), e376 - e376.

http://www.eurekalert.org/pub_releases/2007-04/plos-set041707.php

Sleep protects against interference

A study involving 48 people (aged 18—30) found that those who learned 20 pairs of words at 9pm and were tested at 9am the following morning, after a night’s sleep, performed better than those who learned them at 9am and were tested at 9pm of the same day. Moreover, for those who were given a second list of word pairs to remember just before testing, where the first word in each pair was the same as on the earlier list, the advantage of sleep was dramatically better. For those who experienced the interference manipulation, those in the sleep group recalled 12% more word pairs than the wake group, but with interference, the recall rate was 44% higher for the sleep group.

The findings were presented by Dr Jeffrey Ellenbogen at the American Academy of Neurology’s 59th Annual Meeting in Boston, April 28 – May 5, 2007.

http://www.eurekalert.org/pub_releases/2007-04/aaon-ssy040307.php

Sleeping helps us put facts together

And in yet another sleep study, researchers found evidence that sleep also helps us see the big picture. The study involved 56 students who were shown oval images of colorful abstract patterns nicknamed "Fabergé eggs." Participants were first shown a combination of five pairs of the eggs, all of which were given ratings. The students were given 30 minutes to learn which shape rated higher and so should be chosen over another shape. They were not told the hidden connection that linked all five pairs together. They were then tested either after 20 minutes, after 12 hours, or after 24 hours. Half of those in the 12-hour group slept before the test, the other half did not. The 20-minute group performed the worst, showing no evidence of seeing the pattern. Those who had longer before being tested were much more likely to show signs of inferential judgment (75% vs 52%), and for the most distant (and difficult) inferential judgment, the students who had had periods of sleep in between learning and testing significantly outperformed those who hadn’t slept (93% vs 69%). The researchers are interested in exploring whether meditation can provide a similar benefit.

[749] Ellenbogen, J. M., Hu P. T., Payne J. D., Titone D., & Walker M. P.
(2007).  Human relational memory requires time and sleep.
Proceedings of the National Academy of Sciences. 104(18), 7723 - 7728.

http://www.physorg.com/news98376198.html
http://www.eurekalert.org/pub_releases/2007-04/bidm-tut042007.php

More on how memories are consolidated during sleep

A new study sheds more light on how memory is consolidated during sleep. Using a new technique, the research confirms that new information is transferred between the hippocampus and the cerebral cortex, and, unexpectedly, provides evidence suggesting that the cerebral cortex actively controls this transfer.

[834] Hahn, T. T. G., Sakmann B., & Mehta M. R.
(2006).  Phase-locking of hippocampal interneurons' membrane potential to neocortical up-down states.
Nat Neurosci. 9(11), 1359 - 1361.

http://www.eurekalert.org/pub_releases/2006-12/m-lds120506.php

Still more on how memories are consolidated during sleep

In research following up an earlier study in which rats were shown to form complex memories for sequences of events experienced while they were awake, and that these memories were replayed while they slept, it has been shown that these replayed memories do contain the visual images that were present during the running experience. By showing that the brain is replaying memory events in the visual cortex and in the hippocampus at the same time, the finding suggests that this process may contribute to or reflect the result of the memory consolidation process.

[317] Ji, D., & Wilson M. A.
(2007).  Coordinated memory replay in the visual cortex and hippocampus during sleep.
Nat Neurosci. 10(1), 100 - 107.

http://www.eurekalert.org/pub_releases/2006-12/miot-mtr121806.php

Brainwave oscillations responsible for memory benefits of sleep?

Passing a mild electrical current through the brain while students were asleep improved their ability to remember words on waking up. 13 medical students were given 46 pairs of words to learn. Before sleeping, they remembered an average 37.42 words; after sleep, those not given the stimulation remembered an average of 39.5, while those given the stimulation remembered an average of 41.27. The memory enhancement only occurred at a certain frequency and during a particular part of the sleep cycle, confirming the idea that slow oscillations of electrical activity are responsible for the memory consolidation effects of sleep. The benefit also only applied to fact learning; skill learning was not affected.

[238] Marshall, L., Helgadottir H., Molle M., & Born J.
(2006).  Boosting slow oscillations during sleep potentiates memory.
Nature. 444(7119), 610 - 613.

http://www.guardian.co.uk/science/story/0,,1940475,00.html
http://www.sciam.com/article.cfm?chanID=sa003&articleID=BEC346B2-E7F2-99DF-350CC33BA6757700
http://www.nature.com/news/2006/061030/full/444133a.html

More support that sleep helps consolidate learning

An experiment involving fruitflies has found that those in a social environment with at least 30 other flies slept four times as long during their daytime naps as flies in isolation. There was no difference in night-time sleep. The length of the nap increased with the size of the group they socialized with. Confirming that this effect was due to an increase in social interactions, rather than, for example, physical exhaustion from flying around more, flies deprived of their sight and sense of smell (meaning they could still fly around but could not socialize) showed no difference in daytime sleep patterns. Of 49 genes known to be involved in learning and memory, switching off seventeen (all related to long-term memory) made the flies sleep equally long regardless of whether they were social or not.

[894] Ganguly-Fitzgerald, I., Donlea J., & Shaw P. J.
(2006).  Waking Experience Affects Sleep Need in Drosophila.
Science. 313(5794), 1775 - 1781.

http://www.nature.com/news/2006/060918/full/060918-9.html
http://www.livescience.com/humanbiology/060921_flies_sleep.html

Human study supports value of daytime napping for learning

REM sleep, when most dreaming occurs, has been shown in a number of studies to be important in consolidating procedural (skill) learning, while non-REM (slow-wave) sleep seems to be more important for declarative (knowledge-based) learning. However, because normal sleep contains both REM and non-REM cycles, research hasn’t been able to clearly distinguish the effects. Now a new study using brief daytime napping confirms the role of non-REM sleep for declarative learning. Volunteers who memorized pairs of words and practiced tracing images in a mirror test scored 15% better in the word test if they had been allowed a nap in the six hour period before being tested. However, they did no better at the action test.

[414] Tucker, M. A., Hirota Y., Wamsley E. J., Lau H., Chaklader A., & Fishbein W.
(2006).  A daytime nap containing solely non-REM sleep enhances declarative but not procedural memory.
Neurobiology of Learning and Memory. 86(2), 241 - 247.

Sleep makes memories resistant to interference

It’s pretty clear now that sleep consolidates procedural (skill) learning, but the question of whether or not it helps other types of memory is still very much a matter of debate. However, a new study has found a marked effect of sleep on our ability to remember information. The study involved 60 healthy college-aged adults, who were asked them to memorize 20 pairs of random words. Half were given the words at 9am and tested at 9pm, and the other half were given the words at 9pm and tested at 9am. While the sleepers did perform better (94% recall compared to 82%), it was the introduction of another factor that made the benefits of sleep undeniable. Participants who were given a new set of words to learn just 12 minutes before testing revealed a dramatic difference — sleepers recalled 76% of the original words compared to 32% of the sleepless.

[974] Ellenbogen, J. M., Hulbert J. C., Stickgold R., Dinges D. F., & Thompson-Schill S. L.
(2006).  Interfering with Theories of Sleep and Memory: Sleep, Declarative Memory, and Associative Interference.
Current Biology. 16(13), 1290 - 1294.

http://www.sciencedaily.com/releases/2006/07/060711095912.htm
http://www.sciam.com/article.cfm?chanID=sa003&articleID=0006A257-BBB4-14B2-B8B983414B7F4945

Asleep or awake we retain memory

We’ve learned that skill memory is reinforced during sleep, but now new imaging technology reveals that this kind of reinforcement occurs while we’re awake too — even while we’re learning something new.

[475] Peigneux, P., Orban P., Balteau E., Degueldre C., Luxen A., Laureys S., et al.
(2006).  Offline Persistence of Memory-Related Cerebral Activity during Active Wakefulness.
PLoS Biol. 4(4), e100 - e100.

http://www.eurekalert.org/pub_releases/2006-03/plos-aoa032206.php
http://www.sciencedaily.com/releases/2006/03/060329085308.htm

How sleep improves memory

While previous research has been conflicting, it does now seem clear that sleep consolidates learning of motor skills in particular. A new imaging study involving 12 young adults taught a sequence of skilled finger movements has found a dramatic shift in activity pattern when doing the task in those who were allowed to sleep during the 12 hour period before testing. Increased activity was found in the right primary motor cortex, medial prefrontal lobe, hippocampus and left cerebellum — this is assumed to support faster and more accurate motor output. Decreased activity was found in the parietal cortices, the left insular cortex, temporal pole and fronto-polar region — these are assumed to reflect less anxiety and a reduced need for conscious spatial monitoring. It’s suggested that this is one reason why infants need so much sleep — motor skill learning is a high priority at this age. The findings may also have implications for stroke patients and others who have suffered brain injuries.

[670] Walker, M. P., Stickgold R., Alsop D., Gaab N., & Schlaug G.
(2005).  Sleep-dependent motor memory plasticity in the human brain.
Neuroscience. 133(4), 911 - 917.

http://www.eurekalert.org/pub_releases/2005-06/bidm-ssh062805.php

More evidence that learning is consolidated during sleep

A new study provides more evidence for the role of sleep in the consolidation of long-term memories. In the study, volunteers learned the layout of a virtual town, and were then tested by having to quickly find routes to various locations in the town. Those so trained showed greater activity in their hippocampus and an adjacent learning-related region (compared to those not trained) as they took the route tests, with greater activity correlated with better performance. They also showed greater hippocampal brain activity during sleep. Most importantly, the higher the gain in post-sleep performance on the tests, the higher had been their NREM brain activity during sleep. No such correlation was found in REM brain activity. The findings support the view that spatial memory traces are processed during NREM sleep in humans.

[1182] Aerts, J., Luxen A., Maquet P., Peigneux P., Laureys S., Fuchs S., et al.
(2004).  Are spatial memories strengthened in the human hippocampus during slow wave sleep?.
Neuron. 44(3), 535 - 545.

http://www.eurekalert.org/pub_releases/2004-10/cp-etl102204.php

Mentally, sleep may be as active a state as waking state

Why do we sleep? A question we keep asking. Recent research leads us another step in the road. The study has identified a number of genes upregulated specifically during sleep – at least as many as are turned on while we are awake. These "sleep genes" largely fall into four categories: genes involved in synaptic plasticity (supporting the view that sleep aids memory consolidation); genes underlying translation (supporting observations that protein synthesis increases during sleep); genes regulating membrane and vesicle trafficking; and genes for synthesizing cholesterol (which may be crucial for synapse formation and maintenance, which could, in turn, enhance neural plasticity (the brain's ability to change and learn)). The study also found, to the researchers’ surprise, that the cerebellum showed largely the same pattern of gene-expression during sleep as the cortex.

[1021] Cirelli, C., Gutierrez C. M., & Tononi G.
(2004).  Extensive and divergent effects of sleep and wakefulness on brain gene expression.
Neuron. 41(1), 35 - 43.

More on what goes on during sleep

Brain activity patterns vary during sleep, with particular distinction being made between “REM” sleep and “deep” sleep. Both these phases of sleep have been associated with memory processing. The chemical composition of the brain also varies a great deal in the sleep and wakefulness cycle. New research from Germany now report that some of these differences are crucial in memory formation during sleep. In particular, the level of acetylcholine (a neurotransmitter) is high during wakefulness and REM sleep but drops to the minimum in deep sleep. In an experiment that involved subjects performing two memory tasks – learning 40 pairs of semantically related words, and learning to trace figures seen in a mirror – before sleeping for four hours, it was found that those who were given a cholinesterase inhibitor, (cholinesterase being an enzyme that breaks down acetylcholine), performed significantly less well in the wordlist task on wakening. The mirror-tracing task didn't seem to be affected. This supports the idea that a low level of acetylcholine is necessary for strengthening explicit memory during deep sleep, and fits in with a proposed two-stage model of long-term memory formation, in which the cortex transfers newly acquired experiential data to the hippocampus for processing and temporary storage (a process requiring high levels of acetylcholine), and then, during sleep, the processed memory traces in the hippocampus are relayed back to the cortex for long-term storage. This feedback process is blocked by acetylcholine and, thus, only happens in sleep when the acetylcholine level drops to the minimum.
The research may also have important implications for treating memory loss associated with Alzheimer's disease, as cholinesterase inhibitors are widely used in such treatment. Because of common side-effects of the drug, patients are usually told to take it at night, which may well weaken the drug’s effectiveness.

[999] Gais, S., & Born J.
(2004).  Low acetylcholine during slow-wave sleep is critical for declarative memory consolidation.
Proceedings of the National Academy of Sciences of the United States of America. 101(7), 2140 - 2144.

Now definite? Memories are consolidated during sleep

Researchers of a new study claim that their research finally settles the question of whether or not sleep consolidates new memories. The study involved detailed recording of specific learning- and memory- related areas (hippocampus and forebrain) in the brains of rats. The rats were exposed to four kinds of novel objects. Analysis of brain signals before, during, and after this experience, revealed "reverberations" of distinctive brain wave patterns across all the areas being monitored for up to 48 hours after the novel experience. This pattern was much more prevalent in slow-wave sleep than in REM sleep. Previous studies by the same researchers have found that the activation of genes that affect memory consolidation occurs during REM sleep, not slow-wave sleep. It is proposed that both stages of sleep are important for memory consolidation. Previous studies have tended to focus solely on the hippocampus, and have observed brain activity for a much shorter period.

[793] Ribeiro, S., Gervasoni D., Soares E. S., Zhou Y., Lin S-C., Pantoja J., et al.
(2004).  Long-lasting novelty-induced neuronal reverberation during slow-wave sleep in multiple forebrain areas.
PLoS Biology. 2(1), E24 - E24.

http://www.eurekalert.org/pub_releases/2004-01/dumc-etm011304.php
http://www.eurekalert.org/pub_releases/2004-01/plos-brd011204.php
Full text available at http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0020037

Sleep helps insight

A new German study provides evidence for what we all suspected — “sleeping on” a problem can really work. In the study, participants were given a mathematical puzzle to solve; a puzzle which could be solved by trial-by-trial learning, or almost immediately if participants grasped the hidden rule. After training in the trial-by-trial learning, some of the participants were allowed to sleep through the night, while others were prevented from sleeping. When they returned to the problem eight hours later, those that had slept were twice as likely to realize the rule. Another group that trained in the morning, and were then tested later that day, were also slower at finding the rule, suggesting that the slowness was not solely due to fatigue. Sleep did not, however, help participants who had not had the initial training. It is suggested that sleep can act to restructure new memory representations.

[1382] Wagner, U., Gais S., Haider H., Verleger R., & Born J.
(2004).  Sleep inspires insight.
Nature. 427(6972), 352 - 355.

http://www.sciam.com/article.cfm?chanID=sa003&articleID=000088CE-E9DC-100E-A9DC83414B7F0000
http://www.nature.com/nsu/040119/040119-10.html
http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v427/n6972/abs/nature02223_fs.html

Stages of memory clarified in sleep studies

Two new studies add to our understanding of the effects of sleep on memory. Both studies involved young adults and procedural (skill) learning, and found temporary declines in performance in particular contexts (a brief description of these studies is given here). On the basis of these studies, researchers identified three stages of memory processing: the first stage of memory — its stabilization — seems to take around six hours. During this period, the memory appears particularly vulnerable to being “lost”. The second stage of memory processing — consolidation — occurs during sleep. The third and final stage is the recall phase, when the memory is once again ready to be accessed and re-edited. (see my article on consolidation for more explanation of the processes of consolidation and re-consolidation). The surprising aspect to this is the time it appears to take for memories to initially stabilize. The studies also confirm the role of sleep in the consolidation process.

[1027] Fenn, K. M., Nusbaum H. C., & Margoliash D.
(2003).  Consolidation during sleep of perceptual learning of spoken language.
Nature. 425(6958), 614 - 616.

[518] Walker, M. P., Brakefield T., Allan Hobson J., & Stickgold R.
(2003).  Dissociable stages of human memory consolidation and reconsolidation.
Nature. 425(6958), 616 - 620.

http://www.eurekalert.org/pub_releases/2003-10/bidm-som100703.php
http://www.sciencenews.org/20031011/fob4.asp
http://education.guardian.co.uk/higher/research/story/0,9865,1059138,00.html

More support for the theory that sleep is necessary to consolidate memories

A study used fear conditioning in mice to investigate the effect of sleep deprivation on memory. The mice were given a mild electric shock either in a distinctive setting, or subsequent to a tone. Those who experienced the tone continued to freeze when they heard the tone on the following day, whether or not they had been deprived of sleep. Those who associated the environment with the shock, however, were less likely to freeze after sleep deprivation. Mice who had been deprived of sleep during the five hours following training, spent just 4% of their time frozen when returned to the ‘shock environment’ the following day, compared to 15% among mice who were allowed to sleep during this period. The five hours following training was a critical period – those who were deprived of sleep in the 5-10 hours after training showed no sign of memory impairment. The fact that the context association was affected but not the tone cue, suggests that sleep is affecting processes in the hippocampus (important in context memory but not memory for specific facts or events).

[625] Graves, L. A.
(2003).  Sleep Deprivation Selectively Impairs Memory Consolidation for Contextual Fear Conditioning.
Learning & Memory. 10(3), 168 - 176.

http://www.eurekalert.org/pub_releases/2003-07/uop-sdw070803.php

Another step in understanding how sleep affects memory

The value of sleep for memory takes a further step in being understood in new rodent research, which found that, as the rodents slept, the thalamus at the base of their brains originated bursts of electrical activity (“sleep spindles”), which were then detected in the somatosensory neocortex. Some 50 msec later, the hippocampus responded with a pulse of electricity (a “ripple”). "This neocortical-hippocampal dialogue may provide a selection mechanism for the time-compressed replay of information learned during the day." It’s suggested that the ripple is the hippocampus sending back neat, compact waves of memory to the neocortex where they are filed away for future reference. Most of this activity took place during slow wave sleep, the stage which makes up the majority of the sleep cycle.

[907] Wirth, S., Yanike M., Frank L. M., Smith A. C., Brown E. N., & Suzuki W. A.
(2003).  Single Neurons in the Monkey Hippocampus and Learning of New Associations.
Science. 300(5625), 1578 - 1581.

http://www.eurekalert.org/pub_releases/2003-06/nyu-fir060503.php

Napping reverses information overload

Evidence is mounting that sleep helps information processing and learning. A new study has showed that subjects performing a visual task (reporting the horizontal or vertical orientation of three diagonal bars against a background of horizontal bars in the corner of a computer screen) got worse over the course of four daily practice sessions. However, allowing subjects a 30-minute nap after the second session prevented any further deterioration, and a 1-hour nap actually boosted performance in the third and fourth sessions back to morning levels. It appears that the fatigue is limited to the brain visual system circuits involved in the task. When the image was switched to a different right corner of the computer screen on the fourth practice session, subjects performed about as well as they did in the first session -- or after a short nap. Recordings of brain activity reveal that the 1-hour naps contained more than four times as much deep, or slow wave sleep and rapid eye movement (REM) sleep than the half-hour naps.

[758] Mednick, S. C., Nakayama K., Cantero J. L., Atienza M., Levin A. A., Pathak N., et al.
(2002).  The restorative effect of naps on perceptual deterioration.
Nat Neurosci. 5(7), 677 - 681.

http://www.eurekalert.org/pub_releases/2002-07/niom-np070102.php

Improving motor skills through sleep

People taught a simple motor sequence (to type a sequence of keys on a computer keyboard as quickly and accurately as possible) practised it for 12 minutes and were then re-tested 12 hours later. Those who practised in the morning and tested later that same day improved their performance by about 2%. Those trained in the evening and re-tested after a good night's sleep, however, improved by about 20%. The amount of improvement was directly correlated with the amount of Stage 2 (a stage of non-rapid eye movement or NREM) sleep experienced, particularly late in the night. "This is the part of a good night's sleep that many people will cut short by getting up early in the morning."

[767] Laureys, S., Peigneux P., Perrin F., & Maquet P.
(2002).  Sleep and motor skill learning.
Neuron. 35(1), 5 - 7.

http://www.eurekalert.org/pub_releases/2002-07/hms-pmp070102.php

Controversy over sleep's role in memory

Does sleep play a role in memory or not? Two new research papers reach opposite conclusions. One is from Robert Stickgold, who has published several papers supporting the role of sleep in memory consolidation. But the other is a new review of REM sleep studies concluding that REM (rapid eye movement) sleep, or dreaming, plays little role in memory formation, chiefly on the basis that depriving animals and humans of REM sleep by awakening them or by drug treatments does not impair their ability to form long-term memories. In addition, the time spent in REM sleep does not correlate with learning ability across humans, nor is there a positive relation between amount or intensity of REM sleep and learning ability across species.

[987] Stickgold, R., Hobson J. A., Fosse R., & Fosse M.
(2001).  Sleep, Learning, and Dreams: Off-line Memory Reprocessing.
Science. 294(5544), 1052 - 1057.

[1388] Siegel, J. M.
(2001).  The REM sleep-memory consolidation hypothesis.
Science (New York, N.Y.). 294(5544), 1058 - 1063.

http://www.sciencemag.org/cgi/content/abstract/294/5544/1052
http://www.sciencemag.org/cgi/content/abstract/294/5544/1058

New motor skills consolidated during sleep

An imaging study that sheds light on the gain in performance observed during the day after learning a new task. Following training in a motor skill, certain brain areas appear to be reactived during REM sleep, resulting in an optimization of the network that subtends the subject's visuo–motor response.

[775] van der Linden, M., Cleeremans A., Smith C., Maquet P., Laureys S., Peigneux P., et al.
(2001).  Experience-dependent changes in cerebral functional connectivity during human rapid eye movement sleep.
Neuroscience. 105(3), 521 - 525.

Deep "slow wave" sleep necessary to consolidate memories

Sleep is necessary to consolidate memories. Remembering a new task is more difficult if you don't sleep within 30 hours of learning the task. "Catch-up" sleep on subsequent nights doesn't make up for losing that first night's sleep. Moreover, it appears that the deep "slow wave" sleep that occurs in the first half of the night is the type of sleep necessary to consolidate memories. Other types of memory however, may require "REM" sleep (that occurs while you are dreaming).

Stickgold, R., James, L. & Hobson, J.A. 2000. Visual discrimination learning requires sleep after training. Nature Neuroscience,3, 1237-1238.

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Brain flexibility predicts learning speed

June, 2011

New analytic techniques reveal that functional brain networks are more fluid than we thought.

A new perspective on learning comes from a study in which 18 volunteers had to push a series of buttons as fast as possible, developing their skill over three sessions. New analytical techniques were then used to see which regions of the brain were active at the same time. The analysis revealed that those who learned new sequences more quickly in later sessions were those whose brains had displayed more 'flexibility' in the earlier sessions — that is, different areas of the brain linked with different regions at different times.

At this stage, we don’t know how stable an individual’s flexibility is. It may be that individuals vary significantly over the course of time, and if so, this information could be of use in predicting the best time to learn.

But the main point is that the functional modules, the brain networks that are involved in specific tasks, are more fluid than we thought. This finding is in keeping, of course, with the many demonstrations of damage to one region being compensated by new involvement of another region.

Reference: 

[2212] Bassett, D. S., Wymbs N. F., Porter M. A., Mucha P. J., Carlson J. M., & Grafton S. T.
(2011).  Dynamic reconfiguration of human brain networks during learning.
Proceedings of the National Academy of Sciences. 108(18), 7641 - 7646.

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New insight into insight, and the role of the amygdala in memory

April, 2011

A new study suggests that one-off learning (that needs no repetition) occurs because the amygdala, center of emotion in the brain, judges the information valuable.

Most memory research has concerned itself with learning over time, but many memories, of course, become fixed in our mind after only one experience. The mechanism by which we acquire knowledge from single events is not well understood, but a new study sheds some light on it.

The study involved participants being presented with images degraded almost beyond recognition. After a few moments, the original image was revealed, generating an “aha!” type moment. Insight is an experience that is frequently remembered well after a single occurrence. Participants repeated the exercise with dozens of different images.

Memory for these images was tested a week later, when participants were again shown the degraded images, and asked to recall details of the actual image.

Around half the images were remembered. But what’s intriguing is that the initial learning experience took place in a brain scanner, and to the researchers’ surprise, one of the highly active areas during the moment of insight was the amygdala. Moreover, high activity in the amygdala predicted that those images would be remembered a week later.

It seems the more we learn about the amygdala, the further its involvement extends. In this case, it’s suggested that the amygdala signals to other parts of the brain that an event is significant. In other words, it gives a value judgment, decreeing whether an event is worthy of being remembered. Presumably the greater the value, the more effort the brain puts into consolidating the information.

It is not thought, from the images used, that those associated with high activity in the amygdala were more ‘emotional’ than the other images.

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Working memory has more layers than thought

April, 2011

A new study provides further support for a three-tier model of working memory, where the core only holds one item, the next layer holds up to three, and further items can be passively held ready.

Readers of my books and articles will know that working memory is something I get quite excited about. It’s hard to understate the importance of working memory in our lives. Now a new study tells us that working memory is in fact made up of three areas: a core focusing on one active item, a surrounding area holding at least three more active items (called the outer store), and a wider region containing passive items that have been tagged for later retrieval. Moreover, the core region (the “focus of attention”) has three roles (one more than thought) — it not only directs attention to an item and retrieves it, but it also updates it later, if required.

In two experiments, 49 participants were presented with up to four types of colored shapes on a computer screen, with particular types (eg a red square) confined to a particular column. Each colored shape was displayed in sequence at the beginning with a number from 1 to 4, and then instances of the shapes appeared sequentially one by one. The participants’ task was to keep a count of each shape. Different sequences involved only one shape, or two, three, or four shapes. Participants controlled how quickly the shapes appeared.

Unsurprisingly, participants were slower and less accurate as the set size (number of shape types) increased. There was a significant jump in response time when the set-size increased from one to two, and a steady increase in RT and decline in accuracy as set-size increased from 2 to 4. Responses were also notably slower when the stimulus changed and they had to change their focus from one type of shape to another (this is called the switch cost). Moreover, this switch cost increased linearly with set-size, at a rate of about 240ms/item.

Without getting into all the ins and outs of this experiment and the ones leading up to it, what the findings all point to is a picture of working memory in which:

  • the focus contains only one item,
  • the area outside the focus contains up to three items,
  • this outer store has to be searched before the item can be retrieved,
  • more recent items in the outer store are not found any more quickly than older items in the outer store,
  • focus-switch costs increase as a direct function of the number of items in the outer store,
  • there is (as earlier theorized) a third level of working memory, containing passive items, that is quite separate from the two areas of active storage,
  • that the number of passive items does not influence either response time or accuracy for recalling active items.

It is still unclear whether the passive third layer is really a part of working memory, or part of long-term memory.

The findings do point to the need to use active loads rather than passive ones, when conducting experiments that manipulate cognitive load (for example, requiring subjects to frequently update items in working memory, rather than simply hold some items in memory while carrying out another task).

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Sleep reorganizes your memories

December, 2010

New studies show how sleep sculpts your memories, emphasizing what’s important and connecting it to other memories in your brain.

The role of sleep in consolidating memory is now well-established, but recent research suggests that sleep also reorganizes memories, picking out the emotional details and reconfiguring the memories to help you produce new and creative ideas. In an experiment in which participants were shown scenes of negative or neutral objects at either 9am or 9pm and tested 12 hours later, those tested on the same day tended to forget the negative scenes entirely, while those who had a night’s sleep tended to remember the negative objects but not their neutral backgrounds.

Follow-up experiments showed the same selective consolidation of emotional elements to a lesser degree after a 90-minute daytime nap, and to a greater degree after a 24-hour or even several-month delay (as long as sleep directly followed encoding).

These findings suggest that processes that occur during sleep increase the likelihood that our emotional responses to experiences will become central to our memories of them. Moreover, additional nights of sleep may continue to modify the memory.

In a different approach, another recent study has found that when volunteers were taught new words in the evening, then tested immediately, before spending the night in the sleep lab and being retested in the morning, they could remember more words in the morning than they did immediately after learning them, and they could recognize them faster. In comparison, a control group who were trained in the morning and re-tested in the evening showed no such improvement on the second test.

Deep sleep (slow-wave sleep) rather than rapid eye movement (REM) sleep or light sleep appeared to be the important phase for strengthening the new memories. Moreover, those who experienced more sleep spindles overnight were more successful in connecting the new words to the rest of the words in their mental lexicon, suggesting that the new words were communicated from the hippocampus to the neocortex during sleep. Sleep spindles are brief but intense bursts of brain activity that reflect information transfer between the hippocampus and the neocortex.

The findings confirm the role of sleep in reorganizing new memories, and demonstrate the importance of spindle activity in the process.

Taken together, these studies point to sleep being more important to memory than has been thought. The past decade has seen a wealth of studies establishing the role of sleep in consolidating procedural (skill) memory, but these findings demonstrate a deeper, wider, and more ongoing process. The findings also emphasize the malleability of memory, and the extent to which they are constructed (not copied) and reconstructed.

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Distinguishing between working memory and long-term memory

November, 2010

A study with four brain-damaged people challenges the idea that the hippocampus is the hub of spatial and relational processing for short-term as well as long-term memory.

Because people with damage to their hippocampus are sometimes impaired at remembering spatial information even over extremely short periods of time, it has been thought that the hippocampus is crucial for spatial information irrespective of whether the task is a working memory or a long-term memory task. This is in contrast to other types of information. In general, the hippocampus (and related structures in the mediotemporal lobe) is assumed to be involved in long-term memory, not working memory.

However, a new study involving four patients with damage to their mediotemporal lobes, has found that they were perfectly capable of remembering for one second the relative positions of three or fewer objects on a table — but incapable of remembering more. That is, as soon as the limits of working memory were reached, their performance collapsed. It appears, therefore, that there is, indeed, a fundamental distinction between working memory and long-term memory across the board, including the area of spatial information and spatial-objection relations.

The findings also underscore how little working memory is really capable of on its own (although absolutely vital for what it does!) — in real life, long-term memory and working memory work in tandem.

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Individual differences in ability to gauge your own accuracy

October, 2010

Differences in the size and connectivity of a region in the prefrontal cortex underlie how accurate people are in judging their own performance.

Metamemory or metacognition — your ability to monitor your own cognitive processes — is central to efficient and effective learning. Research has also shown that, although we customarily have more faith in person’s judgment the more confident they are in it, a person’s accuracy and their confidence in their accuracy are two quite separate things (which is not to say it’s not a useful heuristic; just that it’s far from infallible). A new study involving 32 participants has looked at individual differences in judging personal accuracy when assessing a geometric image, comparing these differences to differences in the brain.

The perceptual test used simple stimuli, and each one was customized to the individual's level of skill in order to achieve a score of 71%. In keeping with previous research, there was considerable variation in the participants’ accuracy in assessing their own responses. But the intriguing result was that these differences were reflected in differences in the volume of gray matter in the right anterior prefrontal cortex. Moreover, those who were better at judging their own performance not only had more neurons in that region, but also tended to have denser connections between the region and the white matter connected to it. The anterior prefrontal cortex is associated with various executive functions, and seems to be more developed in humans compared to other animals.

The finding should not be taken to indicate a genetic basis for metacognitive ability. The finding implies nothing about whether the physical differences are innate or achieved by training and experience. However it seems likely that, like most skills and abilities, a lot of it is training.

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