episodic memory

Physical activity linked to better memory for names and faces among older adults

  • A small study adds to evidence that walking improves memory in older adults, and indicates that this is particularly helpful for memory tasks the seniors find challenging.

A small study that fitted 29 young adults (18-31) and 31 older adults (55-82) with a device that recorded steps taken and the vigor and speed with which they were made, has found that those older adults with a higher step rate performed better on memory tasks than those who were more sedentary. There was no such effect seen among the younger adults.

Improved memory was found for both visual and episodic memory, and was strongest with the episodic memory task. This required recalling which name went with a person's face — an everyday task that older adults often have difficulty with.

However, the effect on visual memory had more to do with time spent sedentary than step rate. With the face-name task, both time spent sedentary and step rate were significant factors, and both factors had a greater effect than they had on visual memory.

Depression and hypertension were both adjusted for in the analysis.

There was no significant difference in executive function related to physical activity, although previous studies have found an effect. Less surprisingly, there was also no significant effect on verbal memory.

Both findings might be explained in terms of cognitive demand. The evidence suggests that the effect of physical exercise is only seen when the task is sufficiently cognitively demanding. No surprise that verbal memory (which tends to be much less affected by age) didn't meet that challenge, but interestingly, the older adults in this study were also less impaired on executive function than on visual memory. This is unusual, and reminds us that, especially with small studies, you cannot ignore the individual differences.

This general principle may also account for the lack of effect among younger adults. It is interesting to speculate whether physical activity effects would be found if the younger adults were given much more challenging tasks (either by increasing their difficulty, or selecting a group who were less capable).

Step Rate was calculated by total steps taken divided by the total minutes in light, moderate, and vigorous activities, based on the notion that this would provide an independent indicator of physical activity intensity (how briskly one is walking). Sedentary Time was the total minutes spent sedentary.

http://www.eurekalert.org/pub_releases/2015-11/bumc-slp112415.php

Reference: 

[4045] Hayes SM, Alosco ML, Hayes JP, Cadden M, Peterson KM, Allsup K, Forman DE, Sperling RA, Verfaellie M. Physical Activity Is Positively Associated with Episodic Memory in Aging. Journal of the International Neuropsychological Society [Internet]. 2015 ;21(Special Issue 10):780 - 790. Available from: http://journals.cambridge.org/article_S1355617715000910

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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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Mental imagery training improves multiple sclerosis patients' cognition

  • Difficulties in remembering past events and imagining future ones are often experienced by those with multiple sclerosis.
  • A trial involving patients with MS has found that training in mentally visualizing imaginery scenarios can improve their ability to recall past events.
  • Deficits in event memory and imagination have also been found in older adults, so this finding might have wider application.

Training in a mental imagery technique has been found to help multiple sclerosis patients in two memory domains often affected by the disease: autobiographical memory and episodic future thinking.

The study involved 40 patients with relapsing-remitting MS, all of whom were receiving regular drug therapy and all of whom had significant brain atrophy. Participants were randomly assigned to one of three groups, one of which received the imagery training (17 participants), while the other two were controls — a control receiving a sham verbal training (10) and a control receiving no training (13). The six training sessions lasted two hours and occurred once or twice a week.

The training involved:

  • mental visualization exercises of increasing difficulty, using 10 items that the patient had to imagine and describe, looking at both static aspects (such as color and shape) and an action carried out with the item
  • guided construction exercises, using 5 scenarios involving several characters (so, for example, the patient might start with the general idea of a cook preparing a meal, and be guided through more complexities, such as the type of table, the ingredients being used, etc)
  • self-visualization exercises, in which the patient imagined themselves within a scenario.

Autobiographical memory and episodic future thinking were assessed, before and after, using an adapted version of the Autobiographical Interview, which involves subjects recalling events from earlier periods in their life, in response to specific cue words. The events are supposed to be unique, and the subjects are asked to recall as many details as possible.

Only those receiving the training showed a significant improvement in their scores.

Those who had the imagery training also reported an increase in general self-confidence, with higher levels of control and vitality.

Remembering past events and imagining future ones are crucial cognitive abilities, with more far-reaching impacts than may be immediately obvious. For example, episodic future thought is important for forming and carrying out intentions.

These are also areas which may be affected by age. A recent study, for example, found that older adults are less likely to spontaneously acquire items that would later allow a problem to be solved, and are also less likely to subsequently use these items to solve the problems. An earlier study found that older adults have more difficulty in imagining future experiences.

These results, then, that show us that people with deficits in specific memory domains can be helped by specific training, is not only of interest to those with MS, but also more generally.

http://www.eurekalert.org/pub_releases/2015-08/ip-mvi082515.php

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Movie study confirms older people are more distractible

Idiosyncratic brain activity among older people watching a thriller-type movie adds to evidence that:

  • age may affect the ability to perceive and remember the order of events (explaining why older adults may find it harder to follow complex plots)
  • age affects the ability to focus attention and not be distracted
  • age affects the brain's connectivity — how well connected regions work together.

A study involving 218 participants aged 18-88 has looked at the effects of age on the brain activity of participants viewing an edited version of a 1961 Hitchcock TV episode (given that participants viewed the movie while in a MRI machine, the 25 minute episode was condensed to 8 minutes).

While many studies have looked at how age changes brain function, the stimuli used have typically been quite simple. This thriller-type story provides more complex and naturalistic stimuli.

Younger adults' brains responded to the TV program in a very uniform way, while older adults showed much more idiosyncratic responses. The TV program (“Bang! You're dead”) has previously been shown to induce widespread synchronization of brain responses (such movies are, after all, designed to focus attention on specific people and objects; following along with the director is, in a manner of speaking, how we follow the plot). The synchronization seen here among younger adults may reflect the optimal response, attention focused on the most relevant stimulus. (There is much less synchronization when the stimuli are more everyday.)

The increasing asynchronization with age seen here has previously been linked to poorer comprehension and memory. In this study, there was a correlation between synchronization and measures of attentional control, such as fluid intelligence and reaction time variability. There was no correlation between synchronization and crystallized intelligence.

The greatest differences were seen in the brain regions controlling attention (the superior frontal lobe and the intraparietal sulcus) and language processing (the bilateral middle temporal gyrus and left inferior frontal gyrus).

The researchers accordingly suggested that the reason for the variability in brain patterns seen in older adults lies in their poorer attentional control — specifically, their top-down control (ability to focus) rather than bottom-up attentional capture. Attentional capture has previously been shown to be well preserved in old age.

Of course, it's not necessarily bad that a watcher doesn't rigidly follow the director's manipulation! The older adults may be showing more informed and cunning observation than the younger adults. However, previous studies have found that older adults watching a movie tend to vary more in where they draw an event boundary; those showing most variability in this regard were the least able to remember the sequence of events.

The current findings therefore support the idea that older adults may have increasing difficulty in understanding events — somthing which helps explain why some old people have increasing trouble following complex plots.

The findings also add to growing evidence that age affects functional connectivity (how well the brain works together).

It should be noted, however, that it is possible that there could also be cohort effects going on — that is, effects of education and life experience.

http://www.eurekalert.org/pub_releases/2015-08/uoc-ymt081415.php

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How your brain chunks ‘moments’ into ‘events’

We talk about memory for ‘events’, but how does the brain decide what an event is? How does it decide what is part of an event and what isn’t? A new study suggests that our brain uses categories it creates based on temporal relationships between people, objects, and actions — i.e., items that tend to—or tend not to—pop up near one another at specific times.

05/2013

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Self-imagination helps memory in both healthy and memory-impaired

December, 2012

A small study involving patients with TBI has found that the best learning strategies are ones that call on the self-schema rather than episodic memory, and the best involves self-imagination.

Sometime ago, I reported on a study showing that older adults could improve their memory for a future task (remembering to regularly test their blood sugar) by picturing themselves going through the process. Imagination has been shown to be a useful strategy in improving memory (and also motor skills). A new study extends and confirms previous findings, by testing free recall and comparing self-imagination to more traditional strategies.

The study involved 15 patients with acquired brain injury who had impaired memory and 15 healthy controls. Participants memorized five lists of 24 adjectives that described personality traits, using a different strategy for each list. The five strategies were:

  • think of a word that rhymes with the trait (baseline),
  • think of a definition for the trait (semantic elaboration),
  • think about how the trait describes you (semantic self-referential processing),
  • think of a time when you acted out the trait (episodic self-referential processing), or
  • imagine acting out the trait (self-imagining).

For both groups, self-imagination produced the highest rates of free recall of the list (an average of 9.3 for the memory-impaired, compared to 3.2 using the baseline strategy; 8.1 vs 3.2 for the controls — note that the controls were given all 24 items in one list, while the memory-impaired were given 4 lists of 6 items).

Additionally, those with impaired memory did better using semantic self-referential processing than episodic self-referential processing (7.3 vs 5.7). In contrast, the controls did much the same in both conditions. This adds to the evidence that patients with brain injury often have a particular problem with episodic memory (knowledge about specific events). Episodic memory is also particularly affected in Alzheimer’s, as well as in normal aging and depression.

It’s also worth noting that all the strategies that involved the self were more effective than the two strategies that didn’t, for both groups (also, semantic elaboration was better than the baseline strategy).

The researchers suggest self-imagination (and semantic self-referential processing) might be of particular benefit for memory-impaired patients, by encouraging them to use information they can more easily access (information about their own personality traits, identity roles, and lifetime periods — what is termed the self-schema), and that future research should explore ways in which self-imagination could be used to support everyday memory tasks, such as learning new skills and remembering recent events.

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Dopamine decline underlies episodic memory decline in old age

December, 2012

Findings supporting dopamine’s role in long-term episodic memory point to a decline in dopamine levels as part of the reason for cognitive decline in old age, and perhaps in Alzheimer’s.

The neurotransmitter dopamine is found throughout the brain and has been implicated in a number of cognitive processes, including memory. It is well-known, of course, that Parkinson's disease is characterized by low levels of dopamine, and is treated by raising dopamine levels.

A new study of older adults has now demonstrated the effect of dopamine on episodic memory. In the study, participants (aged 65-75) were shown black and white photos of indoor scenes and landscapes. The subsequent recognition test presented them with these photos mixed in with new ones, and required them to note which photos they had seen before. Half of the participants were first given Levodopa (‘L-dopa’), and half a placebo.

Recognition tests were given two and six hours after being shown the photos. There was no difference between the groups at the two-hour test, but at the six-hour test, those given L-dopa recognized up to 20% more photos than controls.

The failure to find a difference at the two-hour test was expected, if dopamine’s role is to help strengthen the memory code for long-term storage, which occurs after 4-6 hours.

Individual differences indicated that the ratio between the amount of Levodopa taken and body weight is key for an optimally effective dose.

The findings therefore suggest that at least part of the reason for the decline in episodic memory typically seen in older adults is caused by declining levels of dopamine.

Given that episodic memory is one of the first and greatest types of memory hit by Alzheimer’s, this finding also has implications for Alzheimer’s treatment.

Caffeine improves recognition of positive words

Another recent study also demonstrates, rather more obliquely, the benefits of dopamine. In this study, 200 mg of caffeine (equivalent to 2-3 cups of coffee), taken 30 minutes earlier by healthy young adults, was found to improve recognition of positive words, but had no effect on the processing of emotionally neutral or negative words. Positive words are consistently processed faster and more accurately than negative and neutral words.

Because caffeine is linked to an increase in dopamine transmission (an indirect effect, stemming from caffeine’s inhibitory effect on adenosine receptors), the researchers suggest that this effect of caffeine on positive words demonstrates that the processing advantage enjoyed by positive words is driven by the involvement of the dopaminergic system.

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How stress affects your learning

October, 2012

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 OT. Stress Modulates the Engagement of Multiple Memory Systems in Classification Learning. The Journal of Neuroscience [Internet]. 2012 ;32(32):11042 - 11049. Available from: http://www.jneurosci.org/content/32/32/11042

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Sleep learning making a comeback?

August, 2012

Two new studies provide support for the judicious use of sleep learning — as a means of reactivating learning that occurred during the day.

Back when I was young, sleep learning was a popular idea. The idea was that a tape would play while you were asleep, and learning would seep into your brain effortlessly. It was particularly advocated for language learning. Subsequent research, unfortunately, rejected the idea, and gradually it has faded (although not completely). Now a new study may presage a come-back.

In the study, 16 young adults (mean age 21) learned how to ‘play’ two artificially-generated tunes by pressing four keys in time with repeating 12-item sequences of moving circles — the idea being to mimic the sort of sensorimotor integration that occurs when musicians learn to play music. They then took a 90-minute nap. During slow-wave sleep, one of the tunes was repeatedly played to them (20 times over four minutes). After the nap, participants were tested on their ability to play the tunes.

A separate group of 16 students experienced the same events, but without the playing of the tune during sleep. A third group stayed awake, during which 90-minute period they played a demanding working memory task. White noise was played in the background, and the melody was covertly embedded into it.

Consistent with the idea that sleep is particularly helpful for sensorimotor integration, and that reinstating information during sleep produces reactivation of those memories, the sequence ‘practiced’ during slow-wave sleep was remembered better than the unpracticed one. Moreover, the amount of improvement was positively correlated with the proportion of time spent in slow-wave sleep.

Among those who didn’t hear any sounds during sleep, improvement likewise correlated with the proportion of time spent in slow-wave sleep. The level of improvement for this group was intermediate to that of the practiced and unpracticed tunes in the sleep-learning group.

The findings add to growing evidence of the role of slow-wave sleep in memory consolidation. Whether the benefits for this very specific skill extend to other domains (such as language learning) remains to be seen.

However, another recent study carried out a similar procedure with object-location associations. Fifty everyday objects were associated with particular locations on a computer screen, and presented at the same time with characteristic sounds (e.g., a cat with a meow and a kettle with a whistle). The associations were learned to criterion, before participants slept for 2 hours in a MR scanner. During slow-wave sleep, auditory cues related to half the learned associations were played, as well as ‘control’ sounds that had not been played previously. Participants were tested after a short break and a shower.

A difference in brain activity was found for associated sounds and control sounds — associated sounds produced increased activation in the right parahippocampal cortex — demonstrating that even in deep sleep some sort of differential processing was going on. This region overlapped with the area involved in retrieval of the associations during the earlier, end-of-training test. Moreover, when the associated sounds were played during sleep, parahippocampal connectivity with the visual-processing regions increased.

All of this suggests that, indeed, memories are being reactivated during slow-wave sleep.

Additionally, brain activity in certain regions at the time of reactivation (mediotemporal lobe, thalamus, and cerebellum) was associated with better performance on the delayed test. That is, those who had greater activity in these regions when the associated sounds were played during slow-wave sleep remembered the associations best.

The researchers suggest that successful reactivation of memories depends on responses in the thalamus, which if activated feeds forward into the mediotemporal lobe, reinstating the memories and starting the consolidation process. The role of the cerebellum may have to do with the procedural skill component.

The findings are consistent with other research.

All of this is very exciting, but of course this is not a strategy for learning without effort! You still have to do your conscious, attentive learning. But these findings suggest that we can increase our chances of consolidating the material by replaying it during sleep. Of course, there are two practical problems with this: the material needs an auditory component, and you somehow have to replay it at the right time in your sleep cycle.

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Alzheimer’s biomarkers present decades before symptoms

July, 2012

People with a strong genetic risk of early-onset Alzheimer’s have revealed a progression of brain changes that begin 25 years before symptoms are evident.

A study involving those with a strong genetic risk of developing Alzheimer’s has found that the first signs of the disease can be detected 25 years before symptoms are evident. Whether this is also true of those who develop the disease without having such a strong genetic predisposition is not yet known.

The study involved 128 individuals with a 50% chance of inheriting one of three mutations that are certain to cause Alzheimer’s, often at an unusually young age. On the basis of participants’ parents’ medical history, an estimate of age of onset was calculated.

The first observable brain marker was a drop in cerebrospinal fluid levels of amyloid-beta proteins, and this could be detected 25 years before the anticipated age of onset. Amyloid plaques in the precuneus became visible on brain scans 15-20 years before memory problems become apparent; elevated cerebrospinal fluid levels of the tau protein 10-15 years, and brain atrophy in the hippocampus 15 years. Ten years before symptoms, the precuneus showed reduced use of glucose, and slight impairments in episodic memory (as measured in the delayed-recall part of the Wechsler’s Logical Memory subtest) were detectable. Global cognitive impairment (measured by the MMSE and the Clinical Dementia Rating scale) was detected 5 years before expected symptom onset, and patients met diagnostic criteria for dementia at an average of 3 years after expected symptom onset.

Family members without the risky genes showed none of these changes.

The risky genes are PSEN1 (present in 70 participants), PSEN2 (11), and APP (7) — note that together these account for 30-50% of early-onset familial Alzheimer’s, although only 0.5% of Alzheimer’s in general. The ‘Alzheimer’s gene’ APOe4 (which is a risk factor for sporadic, not familial, Alzheimer’s), was no more likely to be present in these carriers (25%) than noncarriers (22%), and there were no gender differences. The average parental age of symptom onset was 46 (note that this pushes back the first biomarker to 21! Can we speculate a connection to noncarriers having significantly more education than carriers — 15 years vs 13.9?).

The results paint a clear picture of how Alzheimer’s progresses, at least in this particular pathway. First come increases in the amyloid-beta protein, followed by amyloid pathology, tau pathology, brain atrophy, and decreased glucose metabolism. Following this biological cascade, cognitive impairment ensues.

The degree to which these findings apply to the far more common sporadic Alzheimer’s is not known, but evidence from other research is consistent with this progression.

It must be noted, however, that the findings are based on cross-sectional data — that is, pieced together from individuals at different ages and stages. A longitudinal study is needed to confirm.

The findings do suggest the importance of targeting the first step in the cascade — the over-production of amyloid-beta — at a very early stage.

Researchers encourage people with a family history of multiple generations of Alzheimer’s diagnosed before age 55 to register at http://www.DIANXR.org/, if they would like to be considered for inclusion in any research.

Reference: 

[2997] Bateman RJ, Xiong C, Benzinger TLS, Fagan AM, Goate A, Fox NC, Marcus DS, Cairns NJ, Xie X, Blazey TM, et al. Clinical and Biomarker Changes in Dominantly Inherited Alzheimer's Disease. New England Journal of Medicine [Internet]. 2012 :120723122607004 - 120723122607004. Available from: http://www.nejm.org/doi/full/10.1056/NEJMoa1202753

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