How memory works

Memory consolidation during sleep depends on coordinated brain activity

  • New research shows memory consolidation requires simultaneous replay with hippocampal 'ripples'. These may depend on deeper processing.

A study involving epilepsy patients who had electrodes implanted into their brain has revealed that memory consolidation during sleep doesn’t simply involve reactivation of the new memories.

Participants were given pictures to memorize, before taking an afternoon nap. Surprisingly, brainwave activity showed that both the pictures participants later remembered and those they later forgot, were reactivated during sleep. What was crucial was not the reactivation of the picture-specific gamma band activity, but its conjunction with “ripples” (extremely rapid fluctuations in activity) in the hippocampus. Only when the reactivation occurred at the same time as the ripples in the hippocampus did participants remember the picture.

What determined whether this happened? The evidence suggests that longer (and thus deeper) processing of the picture is needed, not simply a quick superficial look.

This phenomenon only occurred during nonREM sleep, not during wakefulness (the circumstances of sleep meant little time was spent in REM sleep).

The findings confirm earlier research with rodents.

https://www.eurekalert.org/pub_releases/2018-10/rb-htb100518.php

Paper available at https://www.nature.com/articles/s41467-018-06553-y

Reference: 

[4394] Zhang, H., Fell J., & Axmacher N.
(2018).  Electrophysiological mechanisms of human memory consolidation.
Nature Communications. 9(1), 4103.

 

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Eye movements get re-enacted when we remember

  • An imaging and eye-tracking study has shown that the brain uses eye movements to help us recall remembered images.

A small study has tested the eminent Donald Hebb’s hypothesis that visual imagery results from the reactivation of neural activity associated with viewing images, and that the re-enactment of eye-movement patterns helps both imagery and neural reactivation.

In the study, 16 young adults (aged 20-28) were shown a set of 14 distinct images for a few seconds each. They were asked to remember as many details of the picture as possible so they could visualize it later on. They were then cued to mentally visualize the images within an empty rectangular box shown on the screen.

Brain imaging and eye-tracking technology revealed that the same pattern of eye movements and brain activation occurred when the image was learned and when it was recalled. During recall, however, the patterns were compressed (which is consistent with our experience of remembering, where memories take a much shorter time than the original experiences).

Our understanding of memory is that it’s constructive — when we remember, we reconstruct the memory from separate bits of information in our database. This finding suggests that eye movements might be like a blueprint to help the brain piece together the bits in the right way.

https://www.eurekalert.org/pub_releases/2018-02/bcfg-cga021318.php

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Why we mix up names of people we know well

  • A large survey sheds light on why we have slips of the tongue when we call very familiar people by the wrong name.

We've all done it: used the wrong name when we know the right one perfectly well. And we all know when it's most likely to happen. But here's a study come to reassure us that it's okay, this is just how we roll.

The study, based on five separate surveys of more than 1,700 respondents, finds that these naming errors (when you call someone you know very well by the wrong name) follow a particular pattern that tells us something about how our memory is organized.

Usually the wrong name comes from the same relationship category. So I call one son by the name of the other; on a bad day (e.g. when there's a lot going on, perhaps a lot of people around, and I'm thinking of many other things — say, at Christmas), I might run through both sons, my partner, and my father!

Not just family, you can mix up friends' names too. And the bit that's really enlightening: family members might also be called by the name of the family dog! Interestingly, only the dog; cat owners don't make such slips of the tongue. (Yes, dogs are family; cats not so much.)

Unsurprisingly, phonetic similarity between names is also a factor, although it's less important than relational category. Names with the same beginning or ending sounds, or with shared phonemes (e.g., John and Bob), are more likely to be muddled.

But it's not affected by physical similarity between people — not even by gender (which surprised me, but then, in my household I'm the only female).

More importantly, it's not a function of age. Misnaming errors are common across the board.

http://www.futurity.org/moms-families-dogs-names-1152392/

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Individuals vary in how they remember events

  • Individuals vary in how vividly they remember the past. A new study links this to differences in brain activity which may reflect a stable trait.
  • The finding also has implications for assessments of age-related cognitive decline.

A study involving 66 healthy young adults (average age 24) has revealed that different individuals have distinct brain connectivity patterns that are associated with different ways of experiencing and remembering the past.

The participants completed an online questionnaire on how well they remember autobiographical events and facts, then had their brains scanned. Brain scans found that those with richly-detailed autobiographical memories had higher mediotemporal lobe connectivity to regions at the back of the brain involved in visual perception, whereas those tending to recall the past in a factual manner showed higher mediotemporal lobe connectivity to prefrontal regions involved in organization and reasoning.

The finding supports the idea that those with superior autobiographical memory have a greater ability or tendency to reinstate rich images and perceptual details, and that this appears to be a stable personality trait.

The finding also raises interesting questions about age-related cognitive decline. Many people first recognize cognitive decline in their increasing difficulty retrieving the details of events. But this may be something that is far more obvious and significant to people who are used to retrieving richly-detailed memories. Those who rely on a factual approach may be less susceptible.

http://www.eurekalert.org/pub_releases/2015-12/bcfg-wiy121015.php

Full text available at http://www.sciencedirect.com/science/article/pii/S0010945215003834

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Memory capacity of brain 10 times more than thought

  • New measurements have exploded the previous estimates of the human brain's memory capacity, and also help explain how neurons have such computational power when their energy use is so low.

The question of the brain's capacity usually brings up remarks that the human brain contains about 100 billion neurons. If each one has, say, 1,000 or more connections to other neurons, this produces some 100 trillion connections in which our memory can be held. These connections are between synapses, which change in strength and size when activated. These changes are a critical part of the memory code. In fact, synaptic strength is analogous to the 1s and 0s that computers use to encode information.

But, here's the thing: unlike the binary code of computers, there are more than two sizes available to synapses. On the basis of the not-very-precise tools researchers had available, they had come up with three sizes: small, medium and large. They also had calculated that the difference between the smallest and largest was a factor of 60.

Here is where the new work comes in, because new techniques have enabled researchers to now see that synapses have far more options open to them. Synapses can, it seems, vary by as little as 8%, creating a possible 26 different sizes available, which corresponds to storing 4.7 bits of information at each synapse, as opposed to one or two.

Despite the precision that this 8% speaks to, hippocampal synapses are notoriously unreliable, with signals typically activating the next neuron only 10-20% of the time. But this seeming unreliability is a feature not a bug. It means a single spike isn't going to do the job; what's needed is a stable change in synaptic strength, which comes from repeated and averaged inputs. Synapses are constantly adjusting, averaging out their success and failure rates over time.

The researchers calculate that, for the smallest synapses, about 1,500 events cause a change in their size/ability (20 minutes), while for the largest synapses, only a couple hundred signaling events (1 to 2 minutes) cause a change. In other words, every 2 to 20 minutes, your synapses are going up or down to the next size, in response to the signals they're receiving.

Based on this new information, the new estimate is that the brain can hold at least a petabyte of information, about as much as the World Wide Web currently holds. This is ten times more than previously estimated.

At the moment, only hippocampal neurons have been investigated. More work is needed to determine whether the same is true across the brain.

In the meantime, the work has given us a better notion of how memories are encoded in the brain, increased the potential capacity of the human brain, and offers a new way of thinking about information networks that may enable engineers to build better, more energy-efficient, computers.

http://www.eurekalert.org/pub_releases/2016-01/si-mco012016.php

http://www.scientificamerican.com/article/new-estimate-boosts-the-human-brain-s-memory-capacity-10-fold/

Full text at http://elifesciences.org/content/4/e10778v2

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Birth order has no meaningful effect on personality or IQ

Because this is such a persistent myth, I thought I should briefly report on this massive study that should hopefully put an end to this myth once and for all (I wish! Myths are not so easily squashed.)

This study used data from 377,000 U.S. high school students, and, agreeing with a previous large study, found that first-borns have a one IQ point advantage over later-born siblings, but while statistically significant, this is a difference of no practical significance.

The analysis also found that first-borns tended to be more extroverted, agreeable and conscientious, and had less anxiety than later-borns, — but those differences were “infinitesimally small”, amounting to a correlation of 0.02 (the correlation between birth order and intelligence was .04).

The study controlled for potentially confounding factors, such as a family's economic status, number of children and the relative age of the siblings at the time of the analysis.

A separate analysis of children with exactly two siblings and living with two parents, enabled the finding that there are indeed specific differences between the oldest and a second child, and between second and third children. But the magnitude of the differences was again “minuscule”.

Perhaps it's not fair to say the myth is trounced. Rather, we can say that, yeah, sure, birth order makes a difference — but the difference is so small as not to be meaningful on an individual level.

http://www.eurekalert.org/pub_releases/2015-07/uoia-msb071615.php

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Clarity in short-term memory shows no link with IQ

December, 2010

The two measures of working memory capacity appear to be fully independent, and only one of them is related to intelligence.

The number of items a person can hold in short-term memory is strongly correlated with their IQ. But short-term memory has been recently found to vary along another dimension as well: some people remember (‘see’) the items in short-term memory more clearly and precisely than other people. This discovery has lead to the hypothesis that both of these factors should be considered when measuring working memory capacity. But do both these aspects correlate with fluid intelligence?

A new study presented 79 students with screen displays fleetingly showing either four or eight items. After a one-second blank screen, one item was returned and the subject asked whether that object had been in a particular location previously. Their ability to detect large and small changes in the items provided an estimate of how many items the individual could hold in working memory, and how clearly they remembered them. These measures were compared with individuals’ performance on standard measures of fluid intelligence.

Analysis of data found that these two measures of working memory — number and clarity —are completely independent of each other, and that it was the number factor only that correlated with intelligence.

This is not to say that clarity is unimportant! Only that it is not related to intelligence.

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How the Brain Works

See also

Encoding

Retrieval

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

Learning 'sculpts' the brain's connections

The ‘resting state’ of the brain is characterized by spontaneous brain activity that has not been understood. Now a new study involving 14 volunteers has found that learning a new task causes measurable changes in that activity, and the degree of change reflects how well subjects have learned to perform the task. The volunteers’ brains were scanned while they were doing nothing, during their learning of a visual task, and afterward, while they did nothing. During the task, part of the visual cortex and frontal-parietal areas involved in the control of spatial attention were particularly active. After learning the task over 5-7 days, during the ‘resting state’ each of these two regions was more likely to be active when the other region wasn't. Subjects who were more successful at the task exhibited a higher degree of this "anti-correlation".

Lewis, C. M., Baldassarre, A., Committeri, G., Romani, G. L., & Corbetta, M. (2009). Learning sculpts the spontaneous activity of the resting human brain. Proceedings of the National Academy of Sciences, 106(41), 17558-17563. doi: 10.1073/pnas.0902455106.

http://www.eurekalert.org/pub_releases/2009-10/wuso-csl100809.php

White matter helps brain learn

Research has concentrated on the effects of learning on gray matter, but in a new study involving 24 right-handed volunteers given 6 weeks of training in juggling, white matter was also investigated. It was found that there was not only changes in gray matter in a part of the parietal lobe associated with spatial coordination, but also the myelin in the same region appeared thicker. The gains in both were eroded after four weeks of no juggling. The findings indicate that gray matter and white matter are more interdependent than thought.

Presented at the 15th Annual Meeting of the Organization for Human Brain Mapping held in San Francisco June 18-23.

http://www.the-scientist.com/news/display/55830/

Circadian clock may be critical for remembering what you learn

We know circadian rhythm affects learning and memory in that we find it easier to learn at certain times of day than others, but now a study involving Siberian hamsters has revealed that having a functioning circadian system is in itself critical to being able to remember. The finding has implications for disorders such as Down syndrome and Alzheimer's disease. The critical factor appears to be the amount of the neurotransmitter GABA, which acts to inhibit brain activity. The circadian clock controls the daily cycle of sleep and wakefulness by inhibiting different parts of the brain by releasing GABA. It seems that if it’s not working right, if the hippocampus is overly inhibited by too much GABA, then the circuits responsible for memory storage don't function properly. The effect could be fixed by giving a GABA antagonist, which blocks GABA from binding to synapses. Recent mouse studies have also demonstrated that mice with symptoms of Down syndrome and Alzheimer's also show improved learning and memory when given the same GABA antagonist. The findings may also have implications for general age-related cognitive decline, because age brings about a degradation in the circadian system. It’s also worth noting that the hamsters' circadian systems were put out of commission by manipulating the hamsters' exposure to light, in a technique that was compared to "sending them west three time zones." The effect was independent of sleep duration.

Ruby, N.F. et al 2008. Hippocampal-dependent learning requires a functional circadian system. Proceedings of the National Academy of Sciences, 105 (40), 15593-15598.

http://www.eurekalert.org/pub_releases/2008-10/su-ccm100808.php

The effect of gamma waves on cognitive and language skills in children

Gamma waves are fast, high-frequency brainwaves that spike when higher cognitive processes are engaged. Research suggests that lower levels of gamma power might hinder the brain's ability to bind thoughts together. In the first study of the "resting" gamma power in the frontal cortex in young children (16, 24 and 36 months old), it’s been revealed that those with higher language and cognitive abilities had correspondingly higher gamma power than those with poorer language and cognitive scores. Children with better attention and inhibitory control also had higher gamma power. There were no differences in gamma power based on gender or socio-economic status, but children with a family history of language impairments showed lower levels of gamma activity. The finding may enable more accurate pinpointing of a child’s development, enabling earlier, and better targeted, intervention.

Benasich, A.A. et al. 2008. Early cognitive and language skills are linked to resting frontal gamma power across the first 3 years. Behavioral Brain Research, 195 (2), 215-222.

http://www.eurekalert.org/pub_releases/2008-10/ru-teo102108.php

Balance in inhibition and excitation is key to learning

A new mouse study has revealed not only the mechanism for learning deficits resulting from neurofibromatosis type 1, but also something fundamental about learning. It seems that the deficits in learning experienced by mice with an abnormal version of the Nf1 gene stem from an increased release by inhibitory neurons of the inhibitory neurotransmitter GABA. Moreover, the learning deficits can be reversed with treatments that reign GABA levels back in. The study also found show that GABA levels normally swell when mice learn, suggesting that a balance of GABA, a balance between excitatory and inhibitory signals, may be key. Changes in GABA inhibition have also recently been implicated in an animal model of Down's syndrome.

Cui, Y. et al. 2008. Neurofibromin Regulation of ERK Signaling Modulates GABA Release and Learning. Cell, 135 (3), 549-560.

http://www.eurekalert.org/pub_releases/2008-10/cp-sol102408.php

Deep brain stimulation may improve memory

In a truly serendipitous and surprising development, experimental brain surgery intended to suppress an obese man's appetite using the increasingly successful technique of deep-brain stimulation, induced an intense recollection of an event from his distant past. More tests showed his ability to learn was dramatically improved when the current was switched on and his brain stimulated. Scientists are now applying the technique in the first trial of the treatment in 6 patients with Alzheimer's disease. The effect is surprising in that it involves stimulation of the hypothalamus, a critical region for metabolic regulation, but not one that has ever been associated with memory. However, the best contact was in a place close to the fornix, an arched bundle of fibres that carries signals within the limbic system, which is involved in memory and emotions and is situated next to the hypothalamus. Deep brain stimulation has been used for some time to treat Parkinson’s disease and other movement disorders.

Hamani, C. et al. 2008. Memory Enhancement Induced by Hypothalamic/Fornix Deep Brain Stimulation. Annals of Neurology, 63 (1), 119-123.

http://www.independent.co.uk/news/science/scientists-discover-way-to-reverse-loss-of-memory-775586.html
http://www.eurekalert.org/pub_releases/2008-01/w-dbs012408.php

Brain's voluntary chain-of-command ruled by not 1 but 2 captains

Previous research has shown a large number of brain regions (39) that are consistently active when people prepare for a mental task. It’s been assumed that all these regions work together under the command of one single region. A new study, however, indicates that there are actually two independent networks operating. The cingulo-opercular network (including the dorsal anterior cingulate/medial superior frontal cortex, anterior insula/frontal operculum, and anterior prefrontal cortex) is linked to a "sustain" signal — it turns on at the beginning, hums away constantly during the task, then turns off at the end. In contrast, the frontoparietal network (including the dorsolateral prefrontal cortex and intraparietal sulcus) is active at the start of mental tasks and during the correction of errors. The findings may help efforts to understand the effects of brain injury and develop new strategies to treat such injuries.

Dosenbach, N.U.F. et al. 2007. Distinct brain networks for adaptive and stable task control in humans. Proceedings of the National Academy of Sciences, 104 (26), 11073-11078.

http://www.physorg.com/news101478606.html

How the brain detects novelty

New research suggests that the hippocampus makes predictions of what will happen next by automatically recalling an entire sequence of events in response to a single cue, allowing us to anticipate future events and detect when things do not turn out as expected. Rather than reacting to novelty, the hippocampus seems to act as a comparison device, matching up past and present experience.

Kumaran, D. & Maguire, E.A. 2006. An unexpected sequence of events: Mismatch detection in the human hippocampus. PLoS Biol 4(12): e424. DOI: 10.1371/journal.pbio.0040424
The full text is available at http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0040424

http://www.eurekalert.org/pub_releases/2006-11/wt-tot112406.php

Connections between neurons act as information filters in the brain

Synapses — the connections between brain cells — have long been known to be important in information-processing, but the exact nature of their role has not been clear. Are they a crucial part of the processing itself, or simply part of the transport system? Worryingly, research has suggested that synapses drop up to 90% of all incoming signals — an unreliability difficult to reconcile with the fact that brain as a whole is very reliable. A new study has cast new light on synaptic activity. It turns out that synaptic transmission is highly temperature-dependent. Previous studies had studied isolated groups of neurons at room temperature; the present study recorded data at wormer conditions — almost body temperature. And revealed that excitatory and inhibitory synapses, previously thought to always work against each other, in fact act in concert to identify patterns carrying relevant information in an incoming signal. As a result, meaningful patterns are amplified, and stray noise is discarded. This provides the experimental confirmation needed, for the view that synapses act to filter the “noise” and makes the information processing reliable.

Klyachko,V.A. & Stevens, C.F. 2006. Excitatory and Feed-Forward Inhibitory Hippocampal Synapses Work Synergistically as an Adaptive Filter of Natural Spike Trains. PLoS Biology, 4 (7), DOI: 10.1371/journal.pbio.0040207  Full text available at: http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0040207

http://www.eurekalert.org/pub_releases/2006-06/si-cbn060906.php

Master planners in brain may coordinate other areas' roles in cognitive tasks

Scans of 183 subjects have identified 3 brain areas most consistently active during a variety of cognitive tasks — the dorsal anterior cingulate and the left and right frontal operculum. It’s suggested that these regions coordinate the activities of specialized regions. In a rather lovely analogy, researchers suggested that if the brain in action can be compared to a symphony, with specialized sections required to pitch in at the right time to produce the desired melody, then the regions highlighted by the new study may be likened to conductors. Until now, the function of the opercula has been a mystery; the findings also suggest a rethinking of the role of the cingulate.

Dosenbach, N.U.F. et al. 2006. A core system for the implementation of task sets. Neuron, 50(5), 799-812.

http://www.sciencedaily.com/releases/2006/05/060531165250.htm
http://www.eurekalert.org/pub_releases/2006-05/wuso-mpi053006.php

How brain cells communicate

A new finding has added to our understanding of how brain cells communicate. A protein called syndapin, previously thought to have no major role in nerve communication, has proven to be the molecule that works with a key protein called dynamin to allow the transmission of messages between nerve cells. The finding has implications for the treatment of many neurological disorders.

Anggono, V. et al. 2006. Syndapin I is the phosphorylation-regulated dynamin I partner in synaptic vesicle endocytosis. Nature Neuroscience, 9, 752 – 760.

http://www.sciencedaily.com/releases/2006/05/060526090336.htm

New understanding of how neurons communicate

Although we knew that the release of neurotransmitters at the synapses of neurons causes the voltage inside the neuron to fluctuate continuously — an analog signal — it’s always been thought that the axon was impassable to those fluctuations, and thus that neurons can only communicate with each other through a digital code — that is, by sending out signals whose information is reading in the timing of the pulses. A new study now suggests that the analog signal can indeed travel along the axon, and that the digital signal passed between synapses is influenced by that analog signal. The discovery may lead to a better understanding of disorders such as epilepsy and migraine, both of which involve large changes in the voltage inside neurons.

Shu, Y., Hasenstaub, A., Duque, A., Yu, Y. & McCormick, D.A. 2006. Modulation of intracortical synaptic potentials by presynaptic somatic membrane potential. Nature, advance online publication 12 April 2006.

Rating familiarity: how we do it

Previous research has indicated that recognizing a familiar object is accompanied by a reduction in activity in the medial temporal lobe. A new imaging study has confirmed the reduced activity and demonstrated that the degree of reduction is correlated with the degree of familiarity of the object (a face in this instance). The reduction began very rapidly in the recognition process. The researchers suggested that the graded response of medial temporal structures are what allows us to assess how familiar an object is.

Gonsalves, B.D., Curran, T., Norman, K.A. & Wagner, A.D. 2005. Memory Strength and Repetition Suppression: Multimodal Imaging of Medial Temporal Cortical Contributions to Recognition. Neuron, 47, 751–761.

http://www.eurekalert.org/pub_releases/2005-08/cp-tt082505.php

Single cell recognition research finds specific neurons for concepts

An intriguing study surprises cognitive researchers by showing that individual neurons in the medial temporal lobe are able to recognize specific people and objects. It’s long been thought that concepts such as these require a network of cells, and this doesn’t deny that many cells are involved. However, this new study points to the importance of a single brain cell. The study of 8 epileptic subjects found variable responses from subjects, but within subjects, individuals showed remarkably specific responses to concepts. For example, a single neuron in the left posterior hippocampus of one subject responded to all pictures of actress Jennifer Aniston, and also to Lisa Kudrow, her co-star on the TV hit "Friends", but not to pictures of Jennifer Aniston together with actor Brad Pitt, and not, or only very weakly, to other famous and non-famous faces, landmarks, animals or objects. In another patient, pictures of actress Halle Berry activated a neuron in the right anterior hippocampus, as did a caricature of the actress, images of her in the lead role of the film "Catwoman," and a letter sequence spelling her name. The results suggest an invariant, sparse and explicit code, which might be important in the transformation of complex visual percepts into long-term and more abstract memories.

Quiroga, R.Q., Reddy, L., Kreiman, G., Koch, C & Fried, I. 2005. Invariant visual representation by single neurons in the human brain. Nature, 435, 1102-1107.

http://www.eurekalert.org/pub_releases/2005-06/uoc--scr062005.php

Brain networks change according to cognitive task

Using a newly released method to analyze functional magnetic resonance imaging, researchers have demonstrated that the interconnections between different parts of the brain are dynamic and not static. Moreover, the brain region that performs the integration of information shifts depending on the task being performed. The study involved two language tasks, in which subjects were asked to read individual words and then make a spelling or rhyming judgment. Imaging showed that the lateral temporal cortex (LTC) was active for the rhyming task, while the intraparietal sulcus (IPS) was active for the spelling task. The inferior frontal gyrus (IFG) and the fusiform gyrus (FG) were engaged by both tasks. However, Dynamic Causal Modeling (the new method for analyzing imaging data) revealed that the network took different configurations depending on the goal of the task, with each task preferentially strengthening the influences converging on the task-specific regions (LTC for rhyming, IPS for spelling). This suggests that task specific regions serve as convergence zones that integrate information from other parts of the brain. Additionally, switching between tasks led to changes in the influence of the IFG on the task-specific regions, suggesting the IFG plays a pivotal role in making task-specific regions more or less sensitive. This is consistent with previous studies showing that the IFG is active in many different language tasks and plays a role in integrating brain regions.

Bitan, T., Booth, J.R., Choy, J., Burman, D.D., Gitelman, D.R. & Mesulam, M-M. 2005. Shifts of Effective Connectivity within a Language Network during Rhyming and Spelling. Journal of Neuroscience, 25, 5397-5403.

http://www.eurekalert.org/pub_releases/2005-06/nu-bnc060105.php

First real-time view of developing neurons reveals surprises

New technology and a small see-through fish called a zebra fish have enabled researchers to watch individual neurons mature. Monitoring the hundreds of neurons in the region of the brain that respond to images, the researchers expected to find that young neurons fire in response to a variety of different images, then refine their role over time so that in the adult fish the neurons only respond to images moving in a certain direction or near the left or right side of the visual field. Instead they found that the neurons fired when they sensed only one type of movement as soon as the neurons were old enough to respond to the images. However, they did take time to establish stable connections. Young neurons send out branches in all directions in the hopes that some branches will connect to other neurons and form synapses that transfer information. As the neuron matures, some of these branches form stable synapses while others recede. This trial-and-error process is what establishes the final interconnected mesh of the brain.

Niell, C.M. &Smith, S.J. 2005. Functional Imaging Reveals Rapid Development of Visual Response Properties in the Zebrafish Tectum. Neuron, 45, 941-951.

http://www.eurekalert.org/pub_releases/2005-03/sumc-frv032205.php

Faster neuron transmission in young males

A study of 186 male and 201 female students (aged 18-25) has found that men's brain cells can transmit nerve impulses 4% faster than women's, probably due to the faster increase of white matter in the male brain during adolescence.

Reed, T.E., Vernon, P.A. & Johnson, A.M. 2005. Confirmation of correlation between brain nerve conduction velocity and intelligence level in normal adults. Intelligence, In Press, Corrected Proof, Available online 12 September 2004

http://www.theaustralian.news.com.au/common/story_page/0,5744,12170249%255E2703,00.html

New theory challenges current view of how brain stores long-term memory

The current view of long-term memory storage is that, at the molecular level, new proteins are manufactured (a process known as translation), and these newly synthesized proteins subsequently stabilize the changes underlying the memory. Thus, every new memory results in a permanent representation in the brain. A new theory of memory storage suggests instead that there is no permanent representation. Rather, memories are copied across many different brain networks. The advantage is that it is a highly flexible system, enabling rapid retrieval even of infrequent elements.
The theory suggests that the brain stores long-term memory by rapidly changing the shape of proteins already present at those synapses activated by learning. The theory explains a number of phenomena that are not properly answered by the existing theory. The theory doesn’t disagree with the view that it is the synapse that is modified in response to learning; the disagreement concerns how that synaptic modification occurs. Current theory says it is brought about by recently synthesized proteins; the new theory suggests that learning leads to a post-synthesis (post-translational) synaptic protein modification that results in changes to the shape, activity and/or location of existing synaptic proteins. It is suggested that long-term memory storage relies on a positive-feedback rehearsal system that continually updates or fine-tunes post-translational modification of previously modified synaptic proteins, thus allowing for the continual modifications of memories.

Routtenberg, A. & Rekart, J.L. 2005. Post-translational protein modification as the substrate for long-lasting memory. Trends in Neurosciences, 28 (1), 12-19.

http://www.eurekalert.org/pub_releases/2005-01/nu-ntc011405.php
http://www.sciencedirect.com/science/journal/01662236

Memory mechanism identified

Long-term memories are stored in the brain through strengthening of the connections (synapses) between neurons. Researchers have known for many years that neurons must turn on the synthesis of new proteins for long-term memory storage and synaptic strengthening to occur, but the mechanisms by which neurons accomplish these tasks have remained elusive. Now research has identified a crucial molecular pathway that allows neurons to rapidly boost their production of new proteins. The central component of this pathway, an enzyme called "mitogen-activated protein kinase" (MAPK), effectively provides a molecular switch that triggers long-term memory storage by mobilizing the protein synthesis machinery. The research also reveals that activation of MAPK increased production production of a large number of proteins. Many researchers have thought that only a very limited number of proteins are involved in long-term memory formation.

Kelleher, R.J., Govindarajan, A., Jung, H-Y., Kang, H. & Tonegawa, S. 2004. Translational Control by MAPK Signaling in Long-Term Synaptic Plasticity and Memory. Cell, 116, 467-479.

http://www.eurekalert.org/pub_releases/2004-02/miot-mtd020404.php

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.

Walker, M.P., Brakefield, T., Hobson, J.A. & Stickgold, R. 2003. Dissociable stages of human memory consolidation and reconsolidation. Nature, 425, 616-620.

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

Brain implant may restore memory

An artificial hippocampus — a programmed silicone chip — is to be linked with live tissue taken from rat brains, and then will be tested on live animals. If all goes well, it will then be tested as a way to help people who have suffered brain damage due to stroke, epilepsy or Alzheimer's disease.

http://www.guardian.co.uk/international/story/0,3604,912940,00.html
http://www.newscientist.com/news/news.jsp?id=ns99993488
http://www.eurekalert.org/pub_releases/2003-03/ns-twf031203.php

Fear-conditioning study demonstrates long-suspected link between longterm potentiation and learning

It has long been felt that learning and memory must require physical changes in neurons that increase their responsivity to other neurons, so that they will continue to respond in the long-term even in the absence of external stimuli. Until now, however, noone has been able to actually demonstrate that this long-term potentiation occurs during learning. A new direction has proved to be more successful. Investigation of changes in the amygdala (a part of the brain associated with emotional response) after rats had been trained to fear a sound, found that postsynaptic neurons in the amygdala failed to produce any noticeable increase in electrical current, suggesting they had already been potentiated by their presynaptic partners.

Tsvetkov, E., Carlezon Jr.,W.A., Benes, F.M., Kandel, E.R. & Bolshakov, V.Y. 2002. Fear Conditioning Occludes LTP-Induced Presynaptic Enhancement of Synaptic Transmission in the Cortical Pathway to the Lateral Amygdala. Neuron, 34, 289-300.

Fruit flies might help us discover how the brain knows which brain connections to strengthen

Memory in fruit flies can be improved by boosting the level of a protein called PKM. The research may provide some answers to the burning question of how particular synapses are chosen. While it is generally agreed that memories are stored as changes in the number and strength of the connections between brain neurons (synapses), it has not been known how the particular synapses involved in a memory or learned skill are selected. It is thought that PKM may be involved in a process that 'tags' synapses during memory formation.

Drier, E.A., Tello. M.K., Cowan, M., Wu, P., Blace, N., Sacktor, T.C. & Yin, J.C.P. 2002.Memory enhancement and formation by atypical PKM activity in Drosophila melanogaster. Nature Neuroscience, 5 (4),316–324.

http://www.eurekalert.org/pub_releases/2002-03/cshl-sef032202.php
http://news.bbc.co.uk/hi/english/health/newsid_1894000/1894097.stm

The clearing away of excess glutamate may be important for long-term memory

Experiments with rats have demonstrated that levels of transport molecules for glutamate – chemicals that latch on to and “sweep away” glutamate – increase significantly in the period after the onset of long-term potentiation – the process believed to underlie long-term learning. This suggests that the regulation of glutamate uptake by the transport molecules may be important for maintaining the strength of connections among the neurons. Deficiencies in glutamate transporters have been implicated in neurodegenerative diseases such as amyotrophic lateral sclerosis, or Lou Gherig’s disease.

Levenson, J., Weeber, E., Selcher, J.C., Kategaya, L.S., Sweatt, J.D. & Eskin, A. 2002. Long-term potentiation and contextual fear conditioning increase neuronal glutamate uptake. Nature Neuroscience, 5,155–161.

http://www.eurekalert.org/pub_releases/2002-03/uoh-bcc031202.php

Identification of key brain protein for long-term memory

Using mice, scientists have identified a key brain protein involved in retaining memories, which could help explain why some things are remembered and some are not. The protein CREB (cAMP response element binding protein) apparently primes brain cells to retain long-term memories. Neurons in mice engineered to express a chimeric CREB protein were found to need a smaller first stimulus to generate a lasting increase in synaptic strength (long-term potentiation).

Barco, A., Alarcon, J.M. & Kandel, E.R. 2002. Expression of Constitutively Active CREB Protein Facilitates the Late Phase of Long-Term Potentiation by Enhancing Synaptic Capture. Cell, 108 (5), 689-703.

http://news.bbc.co.uk/hi/english/health/newsid_1862000/1862819.stm

The neural basis for motor learning

Learning happens when a brain cell gets stimulated in a way that reduces its ability to respond to a particular brain messenger called glutamate. In the cerebellum there are very large, strangely shaped brain cells called Purkinje cells that receive more connections than other types of neurons and fire 50 times per second even when you're sleeping. These cells are involved in simple motor learning processes. A recent study provides support for an earlier study that found there are fewer receptors for glutamate on the surface of neurons during long-term synaptic depression, by demonstrating that the other three possible causes for this reduced response to glutamate do not occur.

Linden, D.J. 2001.The expression of cerebellar LTD in culture is not associated with changes in AMPA-receptor kinetics, agonist affinity, or unitary conductance. Proc. Natl. Acad. Sci. USA, 98 (24), 14066-14071.

tags memworks: 

Retrieval

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

The importance of retrieval cues

An imaging study has revealed that it is retrieval cues that trigger activity in the hippocampus, rather than, as often argued, the strength of the memory. The study involved participants learning unrelated word pairs (a process which included making up sentences with the words), then being asked whether various familiar words had been previously seen or not — the words being shown first on their own, and then with their paired cue word. Brain activity for words judged familiar on their own was compared with activity for the same items when shown with context cues. Increased hippocampal activity occurred only with cued recall. Moreover, the amount of activity was not associated with familiarity strength, and recollected items were associated with greater activity relative to highly familiar items.

Cohn, M., Moscovitch, M., Lahat, A., & McAndrews, M. P. (2009). Recollection versus strength as the primary determinant of hippocampal engagement at retrieval. Proceedings of the National Academy of Sciences, 106(52), 22451-22455.

http://www.eurekalert.org/pub_releases/2009-12/uot-dik120709.php

New insights into memory without conscious awareness

An imaging study in which participants were shown a previously studied scene along with three previously studied faces and asked to identify the face that had been paired with that scene earlier has found that hippocampal activity was closely tied to participants' tendency to view the associated face, even when they failed to identify it. Activity in the lateral prefrontal cortex, an area required for decision making, was sensitive to whether or not participants had responded correctly and communication between the prefrontal cortex and the hippocampus was increased during correct, but not incorrect, trials. The findings suggest that conscious memory may depend on interactions between the hippocampus and the prefrontal cortex.

Hannula, D.E. & Ranganath, C. 2009. The Eyes Have It: Hippocampal Activity Predicts Expression of Memory in Eye Movements. Neuron, 63 (5), 592-599.

http://www.eurekalert.org/pub_releases/2009-09/cp-ycb090309.php
http://sciencenow.sciencemag.org/cgi/content/full/2009/910/4?etoc

Brain activity linked to anticipation revealed

Brain scans of students listening to their favorite music CDs has revealed plenty of neural activity during the silence between songs — activity that is absent in those listening to music they had never heard in sequence before. Such anticipatory activity probably occurs whenever we expect any particular action to happen. In this case, the activity took the form of excitatory signals passing from the prefrontal cortex (where planning takes place) to the nearby premotor cortex (which is involved in preparing the body to act).

Leaver, A.M. et al. 2009. Brain Activation during Anticipation of Sound Sequences. Journal of Neuroscience, 29, 2477-2485.

http://www.eurekalert.org/pub_releases/2009-02/gumc-rcw022509.php

How we think before we speak: Making sense of sentences

Analysis of the changes in brain activity that occurred when volunteers heard or read critical sentences as part of a longer text or placed in some other type of context, has revealed how anticipatory and contextual our comprehension is. The brain relates unfolding sentences to earlier ones astonishingly quickly (brain effects usually occur before a word is even finished being spoken), and findings indicate that it does this by trying to predict upcoming information. In addition to the words themselves, the person speaking them is a crucial component in understanding what is being said. The study found brain effects occurring very rapidly when the content of a statement being spoken did not match with the voice of the speaker (e.g. "I have a large tattoo on my back" in an upper-class accent or "I like olives" in a young child's voice). It also appears that grammar is less important than various heuristics that help you arrive at the earliest possible interpretation. Speed is more important than accuracy. “Language comprehension is opportunistic, proactive, and, above all, immediately context-dependent.”

Berkum, J.J.A. 2008. Understanding Sentences in Context: What Brain Waves Can Tell Us. Current Directions in Psychological Science, 17 (6), 376-380.

http://www.physorg.com/news154349880.html

Gut feelings may actually reflect a reliable memory

Recently, there has been increased interest in the power of implicit, or unconscious, memory. In the latest study, participants were briefly shown a series of colorful kaleidoscope images and asked to memorise them. Half the time, they simultaneously heard a spoken single-digit number, which they had to keep in mind until the next trial, when they indicated whether it was odd or even. On every trial they had to listen to a new number and press a button to complete the number task. They were tested a short time after the learning period by having to recognize the images they had seen earlier, from pairs of similar kaleidoscope images. It was found that people were more accurate in selecting the old image when they had been distracted than when they had paid full attention, and were also more accurate when they claimed to be guessing than when they thought an image was familiar. During implicit recognition took place, a different pattern of brain activity was observed than that seen with conscious memory experiences, specifically, frontal-occipital negative brain potentials 200–400 ms after participants saw the old image.

Voss, J.L. & Paller, K.A 2009. An electrophysiological signature of unconscious recognition memory. Nature Neuroscience, 12, 349–355.

http://www.eurekalert.org/pub_releases/2009-02/nu-tgf020509.php

Searching in space is like searching your mind

A study of search modes in both spatial and abstract settings has found evidence that how we look for things, such as our car keys or umbrella, could be related to how we search for more abstract needs, such as words in memory or solutions to problems. The studies compared two search modes: exploitation, where seekers stay with a place or task until they have gotten appreciable benefit from it, and exploration, where seekers move quickly from one place or one task to another, looking for a new set of resources to exploit. In the study, participants "foraged" in a computerized world, moving around until they stumbled upon a hidden supply of resources, then deciding if and when to move on, and in which direction. The scientists tracked their movements. Two different worlds ("clumpy", with fewer but richer resources, and "diffuse", with many more, but much smaller, supplies) encouraged one mode or other. The idea was to "prime" the optimal foraging strategy for each world. The volunteers then participated in a more abstract, intellectual search task -- a computerized game akin to Scrabble. It was found that although the human brain appears capable of using exploration or exploitation search modes depending on the demands of the task, it also has a tendency through "priming" to continue searching in the same way even if in a different domain, such as when switching from a spatial to an abstract task. Moreover, people who have a tendency to use one mode more in one task have a similar tendency to use that mode more in other tasks. The findings also support the view that goal-directed cognition is an evolutionary descendant of spatial-foraging behavior.

Hills, T.T., Todd, P.M. & Goldstone, R.L. 2008. Search in External and Internal Spaces: Evidence for Generalized Cognitive Search Processes. Psychological Science, 19 (8), 802-808.

http://www.eurekalert.org/pub_releases/2008-09/iu-sis090908.php

More light shed on memory retrieval

A new technique has confirmed the idea that when we retrieve memories we try to reinstate our original mindset, when we formed the memory. As you search for memories of a particular event, your brain state progressively comes to resemble the state it was in when you initially experienced the event, as one memory triggers another. They also found patterns of brain activity for specific categories, such as faces, started to emerge approximately five seconds before subjects recalled items from that category — suggesting that participants were bringing to mind the general properties of the images in order to cue for specific details. The technique also enabled researchers to predict with reasonable accuracy what items participants would successfully recall.

Polyn, S.M., Natu, V.S., Cohen, J.D. & Norman, K.A. 2005. Category-Specific Cortical Activity Precedes Retrieval During Memory Search. Science, 310 (5756), 1963–1966.

http://www.eurekalert.org/pub_releases/2005-12/pu-rdn122205.php
http://www.eurekalert.org/pub_releases/2005-12/uop-rkw121905.php

Role of hippocampus in long term memory

The role of the hippocampus in the formation of new memories has been well-documented, and we know that the hippocampus is involved in transferring immediate or short-term memories into long-term memories. However, its specific contribution to the representation of very well-learned information is not well understood. Now a study has recorded the activity of individual hippocampal neurons as monkeys retrieved information from memory, demonstrating significantly different response when the stimuli were well-learned, compared to novel stimuli. This differentiated response in the hippocampus provides strong evidence for a memory signal specific for well-learned information, and suggests a way for well-learned information to be incorporated into everyday memories.

Yanike, M., Wirth, S. & Suzuki, W.A. 2004. Representation of Well-Learned Information in the Monkey Hippocampus. Neuron, 42 (3), 477-487.

http://www.eurekalert.org/pub_releases/2004-05/nyu-ssh051204.php

How we retrieve distant memories

We know that recent memories are stored in the hippocampus, but these memories do not remain there forever. It has been less clear how we retrieve much older memories. Now studies of mice genetically altered to be unable to recall old memories have demonstrated that a part of the cortex called the anterior cingulate is critical for this process. It is suggested that, rather than this structure being the storage site for old memories, the anterior cingulate assembles signals of an old memory from different sites in the brain. Dementia may result from a malfunction in this assembling process, leaving the memory too fragmented to make proper sense. Both ageing and certain aspects of Alzheimer's disease and other dementias are all accompanied by reduced activity in the anterior cingulate.

Frankland, P.W., Bontempi, B., Talton, L.E., Kaczmarek, L. & Silva, A.J. 2004. The Involvement of the Anterior Cingulate Cortex in Remote Contextual Fear Memory. Science, 304, 881-883.

http://news.bbc.co.uk/2/hi/health/3689335.stm

Norepinephrine important in retrieving memories

In the first description of a molecule implicated in recalling memories as opposed to laying down new memories, researchers have found that the neurotransmitter norepinephrine is essential in retrieving certain types of memories. The studies involved mutant mice lacking norepinephrine and rats treated with drugs that block some norepinephrine receptors (beta blockers). The results run counter to currently held hypotheses that suggest that stress hormones like norepinephrine are responsible for the formation of long-term consolidation of emotional memories, instead finding that norepinephrine was critical for retrieving intermediate-term contextual and spatial memories. The research may help us better understand post-traumatic stress disorder (PTSD) and depression, both of which involve alterations in memory retrieval in different ways.

Murchison, C.F., Zhang, X-Y., Zhang, W-P., Ouyang, M., Lee, A. & Thomas, S.A. 2004. A Distinct Role for Norepinephrine in Memory Retrieval. Cell, 117 (1), 131-143.

http://www.eurekalert.org/pub_releases/2004-04/uopm-nii033104.php

tags memworks: 

Encoding

See also

Consolidation

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.

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. doi: 10.1073/pnas.0904823106.

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

Why smells can be so memorable

Confirming the common experience of the strength with which certain smells can evoke emotions or memories, an imaging study has found that, when people were presented with a visual object together with one, and later with a second, set of pleasant and unpleasant odors and sounds, then presented with the same objects a week later, there was unique activation in particular brain regions in the case of their first olfactory (but not auditory) associations. This unique signature existed in the hippocampus regardless of how strong the memory was — that is, it was specific to olfactory associations. Regardless of whether they were smelled or heard, people remembered early associations more clearly when they were unpleasant.

The study appeared online on November 5 in Current Biology.

http://www.physorg.com/news176649240.html

Two studies help explain the spacing effect

I talked about the spacing effect in my last newsletter. Now it seems we can point to the neurology that produces it. Not only that, but the study has found a way of modifying it, to improve learning. It’s a protein called SHP-2 phosphatase that controls the spacing effect by determining how long resting intervals between learning sessions need to last so that long-lasting memories can form. The discovery happened because more than 50% of those with a learning disorder called Noonan's disease have mutations in a gene called PTP11, which encodes the SHP-2 phosphatase protein. These mutations boost the activity levels of SHP-2 phosphatase, which, in genetically modified fruit flies, disturbs the spacing effect by increasing the interval before a new chemical signal can occur (it is the repeated formation and decay of these signals that produces memory). Accordingly, those with the mutation need longer periods between repetitions to establish long-term memory.

Pagani, M.R. et al. 2009. Spacing Effect: SHP-2 Phosphatase Regulates Resting Intervals Between Learning Trials in Long-Term Memory Induction. Cell, 139 (1), 186-198.

http://www.eurekalert.org/pub_releases/2009-10/cshl-csi092809.php

A study involving Aplysia (often used as a model for learning because of its simplicity and the large size of its neural connections) reveals that spaced and massed training lead to different types of memory formation. The changes at the synapses that underlie learning are controlled by the release of the neurotransmitter serotonin. Four to five spaced applications of serotonin generated long-term changes in the strength of the synapse and less activation of the enzyme Protein kinase C Apl II, leading to stronger connections between neurons. However, when the application of serotonin was continuous (as in massed learning), there was much more activation of PKC Apl II, suggesting that activation of this enzyme may block the mechanisms for generating long-term memory, while retaining mechanisms for short-term memory.

Villareal, G., Li, Q., Cai, D., Fink, A. E., Lim, T., Bougie, J. K., et al. (2009). Role of Protein Kinase C in the Induction and Maintenance of Serotonin-Dependent Enhancement of the Glutamate Response in Isolated Siphon Motor Neurons of Aplysia californica. J. Neurosci., 29(16), 5100-5107.

http://www.eurekalert.org/pub_releases/2009-10/mu-wow100109.php

Smart gene helps brain cells communicate

For the second time, scientists have created a smarter rat by making their brains over-express CaMKII, a protein that acts as a promoter and signaling molecule for the NR2B subunit of the NMDA receptor. Over-expressing the gene lets brain cells communicate a fraction of a second longer. The research indicates that it plays a crucial role in initiating long-term potentiation. The NR2B subunit is more common in juvenile brains; after puberty the NR2A becomes more common. This is one reason why young people tend to learn and remember better — because the NR2B keeps communication between brain cells open maybe just a hundred milliseconds longer than the NR2A. Although this genetic modification is not something that could probably be replicated in humans, it does validate NR2B as a drug target for improving memory in healthy individuals as well as those struggling with Alzheimer's or mild dementia.

Wang, D., Cui, Z., Zeng, Q., Kuang, H., Wang, L. P., Tsien, J. Z., et al. (2009). Genetic Enhancement of Memory and Long-Term Potentiation but Not CA1 Long-Term Depression in NR2B Transgenic Rats. PLoS ONE, 4(10), e7486.
Full text at http://dx.plos.org/10.1371/journal.pone.0007486

http://www.eurekalert.org/pub_releases/2009-10/mcog-sr101909.php

Concepts are born in the hippocampus

Concepts are at the heart of cognition. A study showed 25 people pairs of fractal patterns that represented the night sky and asked them to forecast the weather – either rain or sun – based on the patterns. The task could be achieved by either working out the conceptual principles, or simply memorizing which patterns produced which effects. However, the next task required them to make predictions using new patterns (but based on the same principles). Success on this task was predictable from the degree of activity in the hippocampus during the first, learning, phase. In the second phase, the ventromedial prefrontal cortex, important in decision-making, was active. The results indicate that concepts are learned and stored in the hippocampus, and then passed on to the vMPFC for application.

Kumaran, D. et al. 2009. Tracking the Emergence of Conceptual Knowledge during Human Decision Making. Neuron, 63 (6), 889-901.

http://www.newscientist.com/article/dn17862-concepts-are-born-in-the-hippocampus.html
http://www.physorg.com/news172930530.html
http://www.eurekalert.org/pub_releases/2009-09/cp-hwk091709.php

Why we learn more from our successes than our failures

A monkey study shows for the first time how single cells in the prefrontal cortex and basal ganglia change their responses as a result of information about what is the right action and what is the wrong one. Importantly, when a behavior was successful, cells became more finely tuned to what the animal was learning — but after a failure, there was little or no change in the brain, and no improvement in behavior. The finding points to the importance of successful actions in learning new associations.

Histed, M.H., Pasupathy, A. & Miller, E.K. 2009. Learning Substrates in the Primate Prefrontal Cortex and Striatum: Sustained Activity Related to Successful Actions. Neuron, 63 (2), 244-253.

http://www.eurekalert.org/pub_releases/2009-07/miot-wwl072809.php

New insight into how information is encoded in the hippocampus

Theta brain waves are known to orchestrate neuronal activity in the hippocampus, and for a long time it’s been thought that these oscillations were "in sync" across the hippocampus, timing the firing of neurons like a sort of central pacemaker. A new rat study reveals that rather than being in sync, theta oscillations actually sweep along the length of the hippocampus as traveling waves. This changes our notion of how spatial information is represented in the rat brain (and presumably has implications for our brains: theta waves are ubiquitous in mammalian brains). Rather than neurons encoding points in space, it seems that what is encoded are segments of space. This would make it easier to distinguish between representations of locations from different times. It also may have significant implications for understanding how information is transmitted from the hippocampus to other areas of the brain, since different areas of the hippocampus are connected to different areas in the brain. The fact that hippocampal activity forms a traveling wave means that these target areas receive inputs from the hippocampus in a specific sequence rather than all at once.

Lubenov, E.V. & Siapas, A.G. 2009. Hippocampal theta oscillations are travelling waves. Nature, 459, 534-539.

http://www.eurekalert.org/pub_releases/2009-05/ciot-csr052909.php

How the brain translates memory into action

We know that the hippocampus is crucial for place learning, especially for the rapid learning of temporary events (such as where we’ve parked the car). Now a new study reveals more about how that coding for specific places connects to behaviour. Selective lesioning in rats revealed that the critical part is in the middle part of the hippocampus, where links to visuospatial information connect links to the behavioural control necessary for returning to that place after a period of time. Rats whose brain still maintained an accurate memory of place nevertheless failed to find their way when a sufficient proportion of the intermediate hippocampus was removed. The findings emphasise that memory failures are not only, or always, about actual deficits in memory, but can also be about being able to act on it.

Bast, T. et al. 2009. From Rapid Place Learning to Behavioral Performance: A Key Role for the Intermediate Hippocampus. PLoS Biology, 7(4), e1000089.

http://www.physorg.com/news159116757.html
http://www.eurekalert.org/pub_releases/2009-04/plos-nwd041709.php

How what we like defines what we know

How we categorize items is crucial to both how we perceive them and how well we remember them. Expertise in a subject is a well-established factor in categorization — experts create more specific categories. Because experts usually enjoy their areas of expertise, and because time spent on a subject should result in finer categorization, we would expect positive feelings towards an item to result in more specific categories. However, research has found that positive feelings usually result in more global processing. A new study has found that preference does indeed result in finer categorization and, more surprisingly, that this is independent of expertise. It seems that preference itself activates focused thinking that directly targets the preferred object, enabling more detailed perception and finer categorization.

Smallman, R. & Roese, N.J. 2008. Preference Invites Categorization. Psychological Science, 19 (12).

http://www.physorg.com/news152203095.html

Encoding isn’t solely in the hippocampus

Perhaps we can improve memory in older adults with a simple memory trick. The hippocampus is a vital region for learning and memory, and indeed the association of related details to form a complete memory has been thought to occur entirely within this region. However, a new imaging study has found that when volunteers memorized pairs of words such as "motor/bear" as new compound words ("motorbear") rather than separate words, then the perirhinal cortex, rather than the hippocampus, was activated, and this activity predicted whether the volunteers would be able to successfully remember the pairs in the future.

Haskins, A.L. et al. 2008. Perirhinal Cortex Supports Encoding and Familiarity-Based Recognition of Novel Associations. Neuron, 59, 554-560.

http://www.sciencedaily.com/releases/2008/08/080828220519.htm
http://www.eurekalert.org/pub_releases/2008-08/uoc--mts082808.php

Computer model reveals how brain represents meaning

A new computational model has been developed that can predict with 77% accuracy which areas of the brain are activated when a person thinks about a specific concrete noun.  The success of the model points to a new understanding of how our brains represent meaning. The model was constructed on the basis of the frequency with which a noun co-occurs in text (from a trillion-word text corpus) with each of 25 verbs associated with sensory-motor functions, including see, hear, listen, taste, smell, eat, push, drive and lift. These 25 verbs appear to be basic building blocks the brain uses for representing meaning. The effect of each co-occurrence on the activation of each tiny voxel in an fMRI brain scan was established, and from this data, activation patterns were drawn.

Mitchell, T.M. et al. 2008. Predicting Human Brain Activity Associated with the Meanings of Nouns. Science, 320 (5880), 1191-1195.

http://www.physorg.com/news131290235.html
http://www.eurekalert.org/pub_releases/2008-05/cmu-cmc052308.php

Novel mechanism for long-term learning identified

There has always been a paradox at the heart of learning: repetition is vital, yet at the level of individual synapses, repetitive stimulation might actually reverse early gains in synaptic strength. Now the mechanism that resolves this apparent paradox has been uncovered. N-methyl-D-aspartate (NMDA) receptors appear from studies to be required for the synaptic strengthening that occurs during learning, but these receptors undergo a sort of Jekyll-and-Hyde transition after the initial phase of learning. Instead of helping synapses get stronger, they actually begin to weaken the synapses and impair further learning. The new study reveals that while the NMDA receptor is required to begin neural strengthening, a second neurotransmitter receptor — the metabotropic glutamate (mGlu) receptor — then comes into play. Using an NMDA antagonist to block NMDA receptors after the initiation of plasticity resulted in enhanced synaptic strengthening, while blocking mGlu receptors caused strengthening to stop.

Clem, R.L., Celikel, T. & Barth, A.L. 2008. Ongoing in Vivo Experience Triggers Synaptic Metaplasticity in the Neocortex. Science, 319 (5859), 101-104.

http://www.eurekalert.org/pub_releases/2008-01/cmu-nmf010308.php

Brain protein that's a personal trainer for your memory

A brain protein called kalirin has been shown to be critical for helping you learn and remember what you learned. When you learn something new, kalirin makes the synaptic spines on your neurons grow bigger and stronger the more you repeat the lesson. This may help explain why continued intellectual activity and learning delays cognitive decline as people grow older. "It's important to keep learning so your synapses stay healthy." Previous studies have found that kalirin levels are reduced in brains of people with diseases like Alzheimer's and schizophrenia. This latest finding suggests it may be a useful target for future drug therapy for these diseases.

Xie, Z. et al . 2007. Kalirin-7 Controls Activity-Dependent Structural and Functional Plasticity of Dendritic Spines. Neuron, 56, 640-656.

http://www.eurekalert.org/pub_releases/2007-11/nu-wyr112107.php
http://www.eurekalert.org/pub_releases/2007-11/cp-md111407.php

Why learning takes a while

New findings about how new connections are made between brain cells sheds light on why it sometimes takes a little while before we truly ‘get’ something. It seems that, although connections are made within minutes, it takes eight hours before these connections are mature enough to transmit information, and more hours before the connections are firmly enough established to become fully functional synapses, likely to survive. It was also found that when a new spine made contact with a site already hosting a contact, the new spine was highly likely to displace the old connection. This may mean that newly learned information might lead to a fading of older information.

Nägerl, U.V., Köstinger, G., Anderson, J.C., Martin, A.C. & Bonhoeffer, T. 2007. Protracted synaptogenesis after activity-dependent spinogenesis in hippocampal neurons. The Journal of Neuroscience, 27, 8149-8156.

http://www.physorg.com/news106837506.html

How memory networks are formed

We know that memories are encoded in a network of neurons, but how do the neurons “decide” which ones to connect to? A mouse study reveals that the level of a protein called CREB is critical in this decision. The findings suggest a competitive model in which eligible neurons are selected to participate in a memory trace as a function of their relative CREB activity at the time of learning.

Han, J-H et al. 2007. Neuronal Competition and Selection During Memory Formation. Science, 316 (5823), 457-460.

http://www.physorg.com/news96213299.html
http://www.eurekalert.org/pub_releases/2007-04/uoc--uru041707.php

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.

Reder, L.M. et al. 2006. Drug-Induced Amnesia Hurts Recognition, but Only for Memories That Can Be Unitized. Psychological Science, 17(7), 562-

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

Why motivation helps memory

An imaging study has identified the brain region involved in anticipating rewards — specific brain structures in the mesolimbic region involved in the processing of emotions — and revealed how this reward center promotes memory formation. Cues to high-reward scenes that were later remembered activated the reward areas of the mesolimbic region as well as the hippocampus. Anticipatory activation also suggests that the brain actually prepares in advance to filter incoming information rather than simply reacting to the world.

Adcock, R.A., Thangavel, A., Knutson, B., Whitfield-Gabrieli, S. & Gabrieli, J.D.E. 2006. Reward-Motivated Learning: Mesolimbic Activation Precedes Memory Formation. Neuron, 50, 507–517.

http://www.eurekalert.org/pub_releases/2006-05/cp-tbm042706.htm

New view of hippocampus’s role in memory

Amnesiacs have overturned the established view of the hippocampus, and of the difference between long-and short-term memories. It appears the hippocampus is just as important for retrieving certain types of short-term memories as it is for long-term memories. The critical thing is not the age of the memory, but the requirement to form connections between pieces of information to create a coherent episode. The researchers suggest that, for the brain, the distinction between 'long-term' memory and 'short-term' memory are less relevant than that between ‘feature’ memory and ‘conjunction’ memory — the ability to remember specific things versus how they are related. The hippocampus may be thought of as the brain's switchboard, piecing individual bits of information together in context.

Olson, I.R., Page, K., Moore, K.S., Chatterjee, A. & Verfaellie, M. 2006. Working Memory for Conjunctions Relies on the Medial Temporal Lobe. Journal of Neuroscience, 26, 4596 – 4601.

http://www.eurekalert.org/pub_releases/2006-05/uop-aso053106.php

Priming the brain for learning

A new study has revealed that how successfully you form memories depends on your frame of mind beforehand. If your brain is primed to receive information, you will have less trouble recalling it later. Moreover, researchers could predict how likely the participant was to remember a word by observing brain activity immediately prior to presentation of the word.

Otten, L.J., Quayle, A.H., Akram, S., Ditewig, T.A. &Rugg, M.D. 2006. Brain activity before an event predicts later recollection. Nature, published online ahead of print 26February2006

http://www.nature.com/news/2006/060220/full/060220-19.html
http://www.eurekalert.org/pub_releases/2006-02/uoc--uri022806.php
http://www.eurekalert.org/pub_releases/2006-02/ucl-ywr022206.php

A single memory is processed in three separate parts of the brain

A rat study has demonstrated that a single experience is indeed processed differently in separate parts of the brain. They found that when the rats were confined in a dark compartment of a familiar box and given a mild shock, the hippocampus was involved in processing memory for context, while the anterior cingulate cortex was responsible for retaining memories involving unpleasant stimuli, and the amygdala consolidated memories more broadly and influenced the storage of both contextual and unpleasant information.

Malin, E.L. & McGaugh, J.L. 2006. Differential involvement of the hippocampus, anterior cingulate cortex, and basolateral amygdala in memory for context and footshock. Proceedings of the National Academy of Sciences, 103 (6), 1959-1963.

http://www.eurekalert.org/pub_releases/2006-02/uoc--urp020106.php

Resting after new learning may not be laziness

In an intriguing rat study, researchers recorded brain activity while rats ran up and down a straight 1.5-metre run. As the rats ran along the track, the nerve cells fired in a very specific sequence. But to the researchers’ surprise, when the rats were resting, the same brain cells replayed the sequence of electrical firing over and over, but in reverse and speeded up. This is similar to the replay that occurs during sleep and consolidates spatial memory, but the reverse aspect has not been seen before, and is presumed to have something to do with reinforcing the sequence. The researchers suggest this may have general implications.

Foster, D.J. & Wilson, M.A. 2006. Reverse replay of behavioural sequences in hippocampal place cells during the awake state. Nature, advance online publication; published online 12 February 2006

http://www.nature.com/news/2006/060206/full/060206-13.html

Protein that controls how neurons change as a result of experience

Two different research teams have identified a master protein that sheds light on one of neurobiology's biggest mysteries-how neurons change as a result of individual experiences. The protein, myocyte enhancer factor 2 (MEF2), turns on and off genes that control dendritic remodeling, that is the growth and pruning of neurons. In addition, one of the teams has identified how MEF2 switches from one program to the other, that is, from dendrite-promoting to dendrite-pruning, and the researchers have identified some of MEF2's targets. It’s suggested the MEF2 pathway could play a role in autism and other neurodevelopmental diseases, and this discovery could lead to new therapies for a host of diseases in which synapses either fail to form or run rampant.

Flavell, S.W. et al. 2006. Activity-Dependent Regulation of MEF2 Transcription Factors Suppresses Excitatory Synapse Number. Science, 311(5763), 1008-1012. Shalizi, A. et al. 2006. A Calcium-Regulated MEF2 Sumoylation Switch Controls Postsynaptic Differentiation. Science, 311(5763), 1012-1017.

http://www.eurekalert.org/pub_releases/2006-02/hms-rfm022106.php

Concrete evidence of the 'memory code'

I’m always talking about the “memory code”, and its existence is central to theories of memory, but now, for the first time, researchers have found concrete evidence of it. The coding system was discovered during an investigation into how the primary auditory cortex responds to different sounds. Rats were trained with various tones; it was found that the more important the tone, the greater the area of auditory cortex that became tuned to it — in other words, more neurons were involved in storing the information.

Rutkowski, R.G. & Weinberger, N.M. 2005. Encoding of learned importance of sound by magnitude of representational area in primary auditory cortex. Proceedings of the National Academy of Sciences, 102 (38), 13664-13669.

http://www.eurekalert.org/pub_releases/2005-09/uoc--unu090805.php

Seeing the formation of a memory

An optical imaging technique has enabled researchers to visualize changes in nerve connections. The study used genetically modified fruit flies, whose neuronal connections become fluorescent during synaptic transmission. The flies were conditioned to associate a brief puff of an odor with a shock. Using a high-powered microscope to watch the fluorescent signals in flies' brains as they learned, the researchers discovered that a specific set of neurons (projection neurons), had a greater number of active connections with other neurons after the conditioning experiment. These newly active connections appeared within 3 minutes after the experiment, suggesting that the synapses which became active after the learning took place were already formed but remained "silent" until they were needed to represent the new memory. The new synaptic activity disappeared by 7 minutes after the experiment, but the flies continued to avoid the odor they associated with the shock. The study suggests that the earliest representation of a new memory occurs by rapid changes – "like flipping a switch" – in the number of neuronal connections that respond to the odor, rather than by formation of new connections or by an increase in the number of neurons that represent an odor. The fact that the flies continued to show a learned response even after the new synaptic activity waned suggests that other memory traces found at higher levels in the brain took over to encode the memory for a longer period of time.

Yu, D., Ponomarev, A. & Davis, R.L. 2004. Altered representation of the spatial code for odors after olfactory classical conditioning: memory trace formation by synaptic recruitment. Neuron, 42 (3), 437–449.

http://www.eurekalert.org/pub_releases/2004-05/nion-sar051004.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.

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. PNAS, 101, 3184-3189.

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

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