retrieval

Memory genes vary in protecting against age-related cognitive decline

November, 2011

New findings show the T variant of the KIBRA gene improves episodic memory through its effect on hippocampal activity. Another study finds the met variant of the BDNF gene is linked to greater age-related cognitive decline.

Previous research has found that carriers of the so-called KIBRA T allele have been shown to have better episodic memory than those who don’t carry that gene variant (this is a group difference; it doesn’t mean that any carrier will remember events better than any non-carrier). A large new study confirms and extends this finding.

The study involved 2,230 Swedish adults aged 35-95. Of these, 1040 did not have a T allele, 932 had one, and 258 had two.  Those who had at least one T allele performed significantly better on tests of immediate free recall of words (after hearing a list of 12 words, participants had to recall as many of them as they could, in any order; in some tests, there was a concurrent sorting task during presentation or testing).

There was no difference between those with one T allele and those with two. The effect increased with increasing age. There was no effect of gender. There was no significant effect on performance of delayed category cued recall tests or a visuospatial task, although a trend in the appropriate direction was evident.

It should also be noted that the effect on immediate recall, although statistically significant, was not large.

Brain activity was studied in a subset of this group, involving 83 adults aged 55-60, plus another 64 matched on sex, age, and performance on the scanner task. A further group of 113 65-75 year-olds were included for comparison purposes. While in the scanner, participants carried out a face-name association task. Having been presented with face-name pairs, participants were tested on their memory by being shown the faces with three letters, of which one was the initial letter of the name.

Performance on the scanner task was significantly higher for T carriers — but only for the 55-60 age group, not for the 65-75 age group. Activity in the hippocampus was significantly higher for younger T carriers during retrieval, but not encoding. No such difference was seen in the older group.

This finding is in contrast with an earlier, and much smaller, study involving 15 carriers and 15 non-carriers, which found higher activation of the hippocampus in non-T carriers. This was taken at the time to indicate some sort of compensatory activity. The present finding challenges that idea.

Although higher hippocampal activation during retrieval is generally associated with faster retrieval, the higher activity seen in T carriers was not fully accounted for by performance. It may be that such activity also reflects deeper processing.

KIBRA-T carriers were neither more nor less likely to carry other ‘memory genes’ — APOEe4; COMTval158met; BDNFval66met.

The findings, then, fail to support the idea that non-carriers engage compensatory mechanisms, but do indicate that the KIBRA-T gene helps episodic memory by improving the hippocampus function.

BDNF gene variation predicts rate of age-related decline in skilled performance

In another study, this time into the effects of the BDNF gene, performance on an airplane simulation task on three annual occasions was compared. The study involved 144 pilots, of whom all were healthy Caucasian males aged 40-69, and 55 (38%) of whom turned out to have at least one copy of a BDNF gene that contained the ‘met’ variant. This variant is less common, occurring in about one in three Asians, one in four Europeans and Americans, and about one in 200 sub-Saharan Africans.  

While performance dropped with age for both groups, the rate of decline was much steeper for those with the ‘met’ variant. Moreover, there was a significant inverse relationship between age and hippocampal size in the met carriers — and no significant correlation between age and hippocampal size in the non-met carriers.

Comparison over a longer time-period is now being undertaken.

The finding is more evidence for the value of physical exercise as you age — physical activity is known to increase BDNF levels in your brain. BDNF levels tend to decrease with age.

The met variant has been linked to higher likelihood of depression, stroke, anorexia nervosa, anxiety-related disorders, suicidal behavior and schizophrenia. It differs from the more common ‘val’ variant in having methionine rather than valine at position 66 on this gene. The BDNF gene has been remarkably conserved across evolutionary history (fish and mammalian BDNF have around 90% agreement), suggesting that mutations in this gene are not well tolerated.

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Ability to remember memories' origin develops slowly

October, 2011

A study comparing the brains of children, adolescents, and young adults has found that the ability to remember the origin of memories is slow to mature. As with older adults, impaired source memory increases susceptibility to false memories.

In the study, 18 children (aged 7-8), 20 adolescents (13-14), and 20 young adults (20-29) were shown pictures and asked to decide whether it was a new picture or one they had seen earlier. Some of the pictures were of known objects and others were fanciful figures (this was in order to measure the effects of novelty in general). After a 10-minute break, they resumed the task — with the twist that any pictures that had appeared in the first session should be judged “new” if that was the first appearance in the second session. EEG measurements (event-related potentials — ERPs) were taken during the sessions.

ERPs at the onset of a test stimulus (each picture) are different for new and old (repeated) stimuli. Previous studies have established various old/new effects that reflect item and source memory in adults. In the case of item memory, recognition is thought to be based on two processes — familiarity and recollection — which are reflected in ERPs of different timings and location (familiarity: mid-frontal at 300-500 msec; recollection: parietal at 400-70 msec). Familiarity is seen as a fast assessment of similarity, while recollection varies according to the amount of retrieved information.

Source memory appears to require control processes that involve the prefrontal cortex. Given that this region is the slowest to mature, it would not be surprising if source memory is a problematic memory task for the young. And indeed, previous research has found that children do have particular difficulty in sourcing memories when the sources are highly similar.

In the present study, children performed more poorly than adolescents and adults on both item memory and source memory. Adolescents performed more poorly than adults on item memory but not on source memory. Children performed more poorly on source memory than item memory, but adolescents and adults showed no difference between the two tasks.

All groups responded faster to new items than old, and ERP responses to general novelty were similar across the groups — although children showed a left-frontal focus that may reflect the transition from analytic to a more holistic processing approach.

ERPs to old items, however, showed a difference: for adults, they were especially pronounced at frontal sites, and occurred at around 350-450 msec; for children and adolescents they were most pronounced at posterior sites, occurring at 600-800 msec for children and 400-600 msec for adolescents. Only adults showed the early midfrontal response that is assumed to reflect familiarity processing. On the other hand, the late old/new effect occurring at parietal sites and thought to reflect recollection, was similar across all age groups. The early old/new effect seen in children and adolescents at central and parietal regions is thought to reflect early recollection.

In other words, only adults showed the brain responses typical of familiarity as well as recollection. Now, some research has found evidence of familiarity processing in children, so this shouldn’t be taken as proof against familiarity processing in the young. What seems most likely is that children are less likely to use such processing. Clearly the next step is to find out the factors that affect this.

Another interesting point is the early recollective response shown by children and adolescents. It’s speculated that these groups may have used more retrieval cues — conceptual as well as perceptual — that facilitated recollection. I’m reminded of a couple of studies I reported on some years ago, that found that young children were better than adults on a recognition task in some circumstances — because children were using a similarity-based process and adults a categorization-based one. In these cases, it had more to do with knowledge than development.

It’s also worth noting that, in adults, the recollective response was accentuated in the right-frontal area. This suggests that recollection was overlapping with post-retrieval monitoring. It’s speculated that adults’ greater use of familiarity produces a greater need for monitoring, because of the greater uncertainty.

What all this suggests is that preadolescent children are less able to strategically recollect source information, and that strategic recollection undergoes an important step in early adolescence that is probably related to improvements in cognitive control. But this process is still being refined in adolescents, in particular as regards monitoring and coping with uncertainty.

Interestingly, source memory is also one of the areas affected early in old age.

Failure to remember the source of a memory has many practical implications, in particular in the way it renders people more vulnerable to false memories.

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Testing to learn: Best practice

September, 2011

Two studies reaffirm the value of retrieval practice, and suggest how often you need to retrieve each item.

In the first study, undergraduates studied English-Lithuanian word pairs, which were displayed on a screen one by one for 10 seconds. After studying the list, the students practiced retrieving the English words — they had 8 seconds to type in the English word as each Lithuanian word appeared, and those that were correct went to the end of the list to be asked again, and those wrong had to be restudied. Each item was pre-assigned a "criterion level" from one to five — the number of times it needed to be correctly recalled during practice.

In the first experiment, participants took one of four recall tests and one of three recognition tests after a 2-day delay. In the second experiment, in order to eliminate the reminder effect of the recall test, participants were only given a recognition test, after a 1-week delay.

Both experiments found that higher criterion levels led to better memory. More importantly, through the variety of tests, they showed that this occurred on all three kinds of memory tested: associative memory; target memory; cue memory. That is, practicing retrieval of the English word didn’t just improve memory for that word (the target), but also for the Lithuanian word (the cue), and the pairing (association).

While this may seem self-evident to some, it has been thought that only the information being retrieved is strengthened by retrieval practice. The results also emphasize that it is the correct retrieval of the information that improves memory, not the number of times the information is studied.

In a related study, 533 students learned conceptual material via retrieval practice across three experiments. Criterion levels varied from one to four correct retrievals in the initial session. Items also varied in how many subsequent sessions they were exposed to. In one to five testing/relearning sessions, the items were practiced until they were correctly recalled once. Memory was tested one to four months later.

It was found that the number of times items were correctly retrieved on the initial session had a strong initial effect, but this weakened as relearning increased. Relearning had pronounced effects on long-term retention with a relatively minimal cost in terms of additional practice trials.

On the basis of their findings, the researchers recommend that students practice recalling concepts to an initial criterion of three correct recalls and then relearn them three times at widely spaced intervals.

Reference: 

[2457] Vaughn, K. E., & Rawson K. A.
(2011).  Diagnosing Criterion-Level Effects on Memory.
Psychological Science.

Rawson, K.A. & Dunlosky, J. 2011. Optimizing schedules of retrieval practice for durable and efficient learning: How much is enough? Journal of Experimental Psychology: General, Jun 27, 2011, No Pagination Specified. doi: 10.1037/a0023956

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Theta brainwaves improve remembering

September, 2011

New research suggests that successful retrieval depends not only on retrieval cues, but also on your preceding brain state.

What governs whether or not you’ll retrieve a memory? I’ve talked about the importance of retrieval cues, of the match between the cue and the memory code you’re trying to retrieve, of the strength of the connections leading to the code. But these all have to do with the memory code.

Theta brainwaves, in the hippocampus especially, have been shown to be particularly important in memory function. It has been suggested that theta waves before an item is presented for processing lead to better encoding. Now a new study reveals that, when volunteers had to memorize words with a related context, they were better at later remembering the context of the word if high theta waves were evident in their brains immediately before being prompted to remember the item.

In the study, 17 students made pleasantness or animacy judgments about a series of words. Shortly afterwards, they were presented with both new and studied words, and asked to indicate whether the word was old or new, and if old, whether the word had been encountered in the context of “pleasant” or “alive”. Each trial began with a 1000 ms presentation of a simple mark for the student to focus on. Theta activity during this fixation period correlated with successful retrieval of the episodic memory relating to that item, and larger theta waves were associated with better source memory accuracy (memory for the context).

Theta activity has not been found to be particularly associated with greater attention (the reverse, if anything). It seems more likely that theta activity reflects a state of mind that is oriented toward evaluating retrieval cues (“retrieval mode”), or that it reflects reinstatement of the contextual state employed during study.

The researchers are currently investigating whether you can deliberately put your brain into a better state for memory recall.

Reference: 

[2333] Addante, R. J., Watrous A. J., Yonelinas A. P., Ekstrom A. D., & Ranganath C.
(2011).  Prestimulus theta activity predicts correct source memory retrieval.
Proceedings of the National Academy of Sciences. 108(26), 10702 - 10707.

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Retrieval practice is best tool for learning

February, 2011

A large study has found studying scientific text by practicing retrieval produced greater long-term recall than studying by elaborating the information in concept maps.

I’ve talked about the importance of retrieval practice at length, so I’m pleased to report on the latest study to confirm its value. Indeed, this study demonstrates that practicing retrieval is a more effective strategy than elaborative studying.

In two studies, a total of 200 students studied texts on topics from different science disciplines. One group engaged in elaborative studying by creating concept maps. The second group read the texts, then put the material away and practiced recalling the concepts from the text. Both groups performed at about the same level on a test at the end of the study period. However, when the students were tested again a week later, the group that studied by practicing retrieval performed 50% better than the group that studied by creating concept maps.

The test involved understanding as well as memory, with some of the questions asking them to draw connections between things that weren't explicitly stated in the material.

The study also confirms that most students are poor at judging the success of their study habits. Asked to predict which technique would produce better results, most thought that concept mapping would be superior.

The findings should certainly not be taken as a slur on concept mapping, which is a study strategy of proven effectiveness. Moreover, while concept mapping can be used solely as an elaborative study method (as it was in these experiments), it can also be used as a retrieval practice technique.

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One reason for practice tests to improve memory

November, 2010

Why does testing improve memory? A new study suggests one reason is that testing supports the use of more effective encoding strategies.

In an experiment to investigate why testing might improve learning, 118 students were given 48 English-Swahili translation pairs. An initial study trialwas followed by three blocks of practice trials. For one group, the practice trial involved a cued recall test followed by restudy. For the other group, they weren’t tested, but were simply presented with the information again (restudy-only). On both study and restudy trials, participants created keywords to help them remember the association. Presumably the 48 word pairs were chosen to make this relatively easy (the example given in the paper is the easy one of wingu-cloud). A final test was given one week later. In this final test, participants received either the cue only (e.g. wingu), or the cue plus keyword, or the cue plus a prompt to remember their keyword.

The group that were tested on their practice trials performed almost three times better on the final test compared to those given restudy only (providing more evidence for the thesis that testing improves learning). Supporting the hypothesis that this has to do with having more effective keywords, keywords were remembered on the cue+prompt trials more often for the test-restudy group than the restudy-only group (51% vs 34%). Moreover, providing the keywords on the final test significantly improved recall for the restudy-only group, but not the test-restudy group (the implication being that they didn’t need the help of having the keywords provided).

The researchers suggest that practice tests lead learners to develop better keywords, both by increasing the strength of the keywords and by encouraging people to change keywords that aren’t working well.

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[1929] Pyc, M. A., & Rawson K. A.
(2010).  Why Testing Improves Memory: Mediator Effectiveness Hypothesis.
Science. 330(6002), 335 - 335.

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The amnesic effect of daydreaming

August, 2010

A new study shows that daydreaming not only impairs your memory of something you’ve just experienced, but that daydreaming of distant places impairs memory more.

Context is important for memory. Therefore it’s not surprising that shifting your mind’s focus to another context can impair recall — or help you forget. Following on from research finding that thinking about something else blocks access to memories of the recent past, a new study has found that daydreaming about a more distant place impairs memory more compared to daydreaming about a closer place.

The study involved participants being presented with a number of words, then being asked to think either about home or their parents’ house (where they hadn’t been for several weeks) before being shown another list of words. They were then asked to recall as many words from both lists as they could. Those who had thought about home remembered more of the words from the first list than did those who had thought about their parents’ house. In another experiment, those who thought about a vacation within the U.S. remembered more words than those who thought about a vacation abroad.

The findings confirm the importance of context in recall, and point to ways in which you can manipulate your wandering thoughts to either help you remember or forget. I’d be interested to know what recall was like after a delay, however. It might be that the context effects are more pronounced in immediate recall.

Reference: 

[1673] Delaney, P. F., Sahakyan L., Kelley C. M., & Zimmerman C. A.
(2010).  Remembering to Forget.
Psychological Science. 21(7), 1036 - 1042.

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