Memory Problems

Why acute stress makes it hard to think properly

A rat study indicates that acute stress disrupts feedback loops in the prefrontal cortex that may be keeping information alive in working memory.

Stress is a major cause of workplace accidents, and most of us are only too familiar with the effects of acute stress on our thinking. However, although the cognitive effects are only too clear, research has had little understanding of how stress has this effect. A new rat study sheds some light.

In the study, brain activity was monitored while five rats performed a working memory task during acute noise stress. Under these stressful conditions, the rats performed dramatically worse on their working memory task, with performance dropping from an average of 93% success to 65%.

The stress also significantly increased the discharge rate of a subset of neurons in the medial prefrontal cortex during two phases of the task: planning and assessment.

This brain region is vital for working memory and executive functions such as goal maintenance and emotion regulation. The results suggest that the firing and re-firing of these neurons keeps recent information ‘fresh’. When the re-firing is delayed, the information can be lost.

What seems to be happening is that the stress is causing these neurons to work even more furiously, but instead of performing their normal task — concentrating on keeping important information ‘alive’ during brief delays — they are reacting to all the other, distracting and less relevant, stimuli.

The findings contradict the view that stress simply suppresses prefrontal cortex activity, and suggests a different approach to treatment, one that emphasizes shutting out distractions.

The findings are also exciting from a theoretical viewpoint, suggesting as they do that this excitatory recursive activity of neurons within the prefrontal cortex provide the neural substrate for working memory. That is, that we ‘hold’ information in the front of our mind through reverberating feedback loops within this network of neurons, that keep information alive during the approximately 1.5 seconds of our working memory ‘span’.

How stress affects your learning

A small study shows that stress makes it more likely for learning to use more complicated and subconscious processes that involve brain regions involved in habit and procedural learning.

We know that stress has a complicated relationship with learning, but in general its effect is negative, and part of that is due to stress producing anxious thoughts that clog up working memory. A new study adds another perspective to that.

The brain scanning study involved 60 young adults, of whom half were put under stress by having a hand immersed in ice-cold water for three minutes under the supervision of a somewhat unfriendly examiner, while the other group immersed their hand in warm water without such supervision (cortisol and blood pressure tests confirmed the stress difference).

About 25 minutes after this (cortisol reaches peak levels around 25 minutes after stress), participants’ brains were scanned while participants alternated between a classification task and a visual-motor control task. The classification task required them to look at cards with different symbols and learn to predict which combinations of cards announced rain and which sunshine. Afterward, they were given a short questionnaire to determine their knowledge of the task. The control task was similar but there were no learning demands (they looked at cards on the screen and made a simple perceptual decision).

In order to determine the strategy individuals used to do the classification task, ‘ideal’ performance was modeled for four possible strategies, of which two were ‘simple’ (based on single cues) and two ‘complex’ (based on multiple cues).

Here’s the interesting thing: while both groups were successful in learning the task, the two groups learned to do it in different ways. Far more of the non-stressed group activated the hippocampus to pursue a simple and deliberate strategy, focusing on individual symbols rather than combinations of symbols. The stressed group, on the other hand, were far more likely to use the striatum only, in a more complex and subconscious processing of symbol combinations.

The stressed group also remembered significantly fewer details of the classification task.

There was no difference between the groups on the (simple, perceptual) control task.

In other words, it seems that stress interferes with conscious, purposeful learning, causing the brain to fall back on more ‘primitive’ mechanisms that involve procedural learning. Striatum-based procedural learning is less flexible than hippocampus-based declarative learning.

Why should this happen? Well, the non-conscious procedural learning going on in the striatum is much less demanding of cognitive resources, freeing up your working memory to do something important — like worrying about the source of the stress.

Unfortunately, such learning will not become part of your more flexible declarative knowledge base.

The finding may have implications for stress disorders such as depression, addiction, and PTSD. It may also have relevance for a memory phenomenon known as “forgotten baby syndrome”, in which parents forget their babies in the car. This may be related to the use of non-declarative memory, because of the stress they are experiencing.

Reference: 

[3071] Schwabe, L., & Wolf O. T. (2012).  Stress Modulates the Engagement of Multiple Memory Systems in Classification Learning. The Journal of Neuroscience. 32(32), 11042 - 11049.

Quick therapy may reduce post-traumatic stress when delivered immediately

A pilot study supports the value of brief cognitive therapy for victims of traumatic events, when delivered as soon as possible after the event. The benefit appears greatest for sexual assault victims.

A new study has found that, when delivered quickly, a modified form of prolonged exposure therapy reduces post-traumatic stress reactions and depression.

The study involved 137 patients being treated in the emergency room of a major trauma center in Atlanta. The patients were chosen from survivors of traumatic events such as rape, car or industrial accidents, and shooting or knife attacks. Participants were randomly assigned to either receive three sessions of therapy beginning in the emergency department (an average of 12 hours after the event), or assessment only. Stress reactions were assessed at 4 and 12 weeks, and depression at baseline and 4 weeks.

Those receiving the therapy reported significantly lower post-traumatic stress at 4 weeks and 12 weeks, and significantly lower depression at 4 weeks. Analysis of subgroups revealed that the therapy was most effective in rape victims. In the cases of transport accidents and physical (non-sexual) assault, the difference between therapy and assessment-only was only barely significant (for transport at 4 weeks) or non-significant. In both subgroups, the effect was decidedly less at 12 weeks than at 4 weeks.

The therapy, carried out by trained therapists, involved participants describing the trauma they had experienced while the therapist recorded the description. The bulk of the hour-long session was taken up with reliving and processing the experience. There were three sessions spaced a week apart. The patients were instructed to listen to their recordings every day, and 85% were compliant. The therapists also explained normal reactions to trauma, helped the patients look at obtrusive thoughts of guilt or responsibility, and taught them a brief breathing or relaxation technique and self care.

While this study doesn’t itself compare the effects of immediate vs delayed therapy, the assumption that delivering the therapy so soon after the trauma is a crucial factor in its success is in line with other research (mainly to do with fear-conditioning in rodent and human laboratory studies). Moreover, while brief cognitive-behavioral therapy has previously been shown to be effective with people diagnosed with acute stress disorder, such therapy is normally begun some 2-4 weeks after trauma, and a study of female assault survivors found that although such therapy did indeed accelerate recovery compared with supportive counseling, after 9 months, PTSD severity was similar in both groups.

Another, severe, limitation of this study is that the therapy involved multiple items. We cannot assume that it was the repeated re-experiencing of the event that is critical.

However, this study is only a pilot study, and its findings are instructive rather than decisive. But at the least it does support the idea that immediate therapy is likely to help victims of trauma recover more quickly.

One final, important, note: It should not, of course, be assumed that simply having the victim describe the events — say to police officers — is in itself therapeutic. Done badly, that experience may itself be traumatic.

Frequent 'heading' in soccer can lead to brain injury and cognitive impairment

A small study extends the evidence that even mild concussions can cause brain damage, with the finding that frequent heading of the ball in soccer can cause similar damage.

American football has been in the news a lot in recent years, as evidence has accumulated as to the brain damage incurred by professional footballers. But American football is a high-impact sport. Soccer is quite different. And yet the latest research reveals that even something as apparently unexceptional as bouncing a ball off your forehead can cause damage to your brain, if done often enough.

Brain scans on 32 amateur soccer players (average age 31) have revealed that those who estimated heading the ball more than 1,000-1,500 times in the past year had damage to white matter similar to that seen in patients with concussion.

Six brain regions were seen to be affected: one in the frontal lobe and five in the temporo-occipital cortex. These regions are involved in attention, memory, executive functioning and higher-order visual functions. The number of headings (obviously very rough estimates, based presumably on individuals’ estimates of how often they play and how often they head the ball on average during a game) needed to produce measurable decreases in the white matter integrity varied per region. In four of temporo-occipital regions, the threshold number was around 1500; in the fifth it was only 1000; in the frontal lobe, it was 1300.

Those with the highest annual heading frequency also performed worse on tests of verbal memory and psychomotor speed (activities that require mind-body coordination, like throwing a ball).

This is only a small study and clearly more research is required, but the findings indicate that we should lower our ideas of what constitutes ‘harm’ to the brain — if repetition is frequent enough, even mild knocks can cause damage. This adds to the evidence I discussed in a recent blog post, that even mild concussions can produce long-lasting trauma to the brain, and it is important to give your brain time to repair itself.

At the moment we can only speculate on the effect such repetition might have to the vulnerable brains of children.

The researchers suggest that heading should be monitored to prevent players exceeding unsafe exposure thresholds.

Reference: 

Kim, N., Zimmerman, M., Lipton, R., Stewart, W., Gulko, E., Lipton, M. & Branch, C. 2011. PhD Making Soccer Safer for the Brain: DTI-defined Exposure Thresholds for White Matter Injury Due to Soccer Heading. Presented November 30 at the annual meeting of the Radiological Society of North America (RSNA) in Chicago.

Brain prosthetic restores learning capability in rats

Effective patterns of neural activity replayed via an artificial device inserted in the hippocampus restores lost learning capability and even improves learning in normal rats.

In the experiment, rats learned which lever to press to receive water, where the correct lever depended on which lever they had pressed previously (the levers were retractable; there was a variable delay between the first and second presentation of the levers). Microelectrodes in the rats’ brains provided data that enabled researchers to work out the firing patterns of neurons in CA1 that resulted from particular firing patterns in CA3 (previous research had established that long-term memory involves CA3 outputs being received in CA1).

Normal neural communication between these two subregions of the hippocampus was then chemically inhibited. While the rats still remembered the general rule, and still remembered that pressing the levers would gain them water, they could only remember which lever they had pressed for 5-10 seconds.

An artificial hippocampal system that could reproduce effective firing patterns (established in earlier training) was then implanted in the rats’ brains and long-term memory function was restored. Furthermore, when the ‘memory prosthetic’ was implanted in animals whose hippocampus was functioning normally, their memory improved.

The findings open up amazing possibilities for ameliorating brain damage. There is of course the greatly limiting factor that effective memory traces (spatiotemporal firing patterns) need to be recorded for each activity. This will be particularly problematic for individuals with significant damage. Perhaps one day we will all ‘record’ ourselves as a matter of course, in the same way that we might put by blood or genetic material ‘in case’! Still, it’s an exciting development.

The next step will be to repeat these results in monkeys.

Reference: 

Sleep deprivation eliminates fear generalization

In a small study, a sleepless night after trauma prevents the development of PTSD symptoms.

Given all the research showing the importance of sleep for consolidating memories, it should come as no great surprise that the reverse is also true: depriving yourself of sleep could help you forget experiences you would prefer not to remember.

In the study, 28 student volunteers were shown 14 short video clips, half of which showed safe driving down a city street, and half showed the car being involved in a nasty crash. Half of the volunteers were then deprived of sleep while the other half received a normal night's sleep. The next day, they were shown pictures and asked to indicate whether they had appeared in the clips they had seen. They were also asked to rate the fear evoked by the image, and their physiological responses measured. They were tested again 3 and 10 days later.

While there was no difference between the two groups in picture recognition, the control group rated the images from the crash videos as fearful, and these responses generalized over time to the other images. However, those who were sleep deprived showed such reactions only on the first day.

The finding suggests a possible therapy for PTSD or other anxiety disorders.

Drug prevents post-traumatic stress syndrome

A new drug is successful in preventing PTSD in mice if delivered within 5 hours of the trauma.

A mouse study has revealed the brain becomes overly stimulated after a traumatic event causes an ongoing, frenzied interaction between two brain proteins long after they should have disengaged. However, the injection of newly developed drugs into the hippocampus within a five hour window calmed this process, and prevented the development of a post-traumatic fear response.

The new research shows the potential for PTSD occurs when a stressful event causes a flood of glutamate, which then interacts with a second protein (Homer1a). This protein continues to stimulate metabotropic glutamate receptor 5 [mGluR5] after the glutamate has dissipated. The new drugs bind mGluR5 and reverse its activity.

Tetris can reduce PTSD flashbacks

Playing Tetris shortly after a traumatic event reduced flashbacks, but playing a word-based quiz increased the number of flashbacks.

Following a study showing that playing Tetris after traumatic events could reduce memory flashbacks in healthy volunteers, two experiments have found playing Tetris after viewing traumatic images significantly reduced flashbacks while playing Pub Quiz Machine 2008 (a word-based quiz game) increased the frequency of flashbacks. In the experiments, volunteers were shown a film that included traumatic images of injury.

In the first experiment, after waiting for 30 minutes, 20 volunteers played Tetris for 10 minutes, 20 played Pub Quiz for 10 minutes and 20 did nothing. In the second experiment, this wait was extended to four hours, with 25 volunteers in each group.

In both experiments, those who played Tetris had significantly fewer flashbacks that the other two groups, and all groups were equally able to recall specific details of the film. Flashbacks were monitored for a week.

It is thought that with traumatic information, perceptual information is emphasized over conceptual information, meaning we are less likely to remember the experience of being in a high-speed road traffic collision as a coherent story, and more likely to remember it by the flash of headlights and noise of a crash. This perceptual information then pops up repeatedly in the victim's mind in the form of flashbacks to the trauma causing great emotional distress, as little conceptual meaning has been attached to them. If you experience other events that involve similar information, during the time window in which the traumatic memories are being processed, that information will interfere with that processing.

Thus, the spatial tasks of Tetris (which involves moving and rotating shapes) are thought to compete with the images of trauma, while answering general knowledge questions in the Pub Quiz game competes with remembering the contextual meaning of the trauma, so the visual memories are reinforced and the flashbacks are increased.

Face-blindness an example of inability to generalize

It seems that prosopagnosia can be, along with perfect pitch and eidetic memory, an example of what happens when your brain can’t abstract the core concept.

‘Face-blindness’ — prosopagnosia — is a condition I find fascinating, perhaps because I myself have a touch of it (it’s now recognized that this condition represents the end of a continuum rather than being an either/or proposition). The intriguing thing about this inability to recognize faces is that, in its extreme form, it can nevertheless exist side-by-side with quite normal recognition of other objects.

Prosopagnosia that is not the result of brain damage often runs in families, and a study of three family members with this condition has revealed that in some cases at least, the inability to remember faces has to do with failing to form a mental representation that abstracts the essence of the face, sans context. That is, despite being fully able to read facial expressions, attractiveness and gender from the face (indeed one of the family members is an artist who has no trouble portraying fully detailed faces), they couldn’t cope with changes in lighting conditions and viewing angles.

I’m reminded of the phenomenon of perfect pitch, which is characterized by an inability to generalize across acoustically similar tones, so an A in a different key is a completely different note. Interestingly, like prosopagnosia, perfect pitch is now thought to be more common than has been thought (recognition of it is of course limited by the fact that some musical expertise is generally needed to reveal it). This inability to abstract or generalize is also a phenomenon of eidetic memory, and I have spoken before of the perils of this.

(Note: A fascinating account of what it is like to be face-blind, from a person with the condition, can be found at: http://www.choisser.com/faceblind/)

1 in 40 of us really can multitask

A study assessing multitasking ability has found that a very few (5 out of 200) were unaffected by doing two complex tasks simultaneously (indeed their performance on the memory task improved!).

A study assessing the performance of 200 people on a simulated freeway driving task, with or without having a cell phone conversation that involved memorizing words and solving math problems, has found that, as expected, performance on both tasks was significantly impaired. However, for a very few, performance on these tasks was unaffected (indeed their performance on the memory task improved!). These few people — five of them (2.5%) — also performed substantially better on these tasks when performed alone.

Reference: 

Watson, J.M. & Strayer, D.L. 2010. Supertaskers: Profiles in extraordinary multitasking ability. Psychonomic Bulletin and Review. In Press.

Full text is available at http://www.psych.utah.edu/lab/appliedcognition/publications/supertaskers...

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