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.

I have said before that there is little evidence that working memory training has any wider benefits than to the skills being practiced. Occasionally a study arises that gets everyone all excited, but by and large training only benefits the skill being practiced — despite the fact that working memory underlies so many cognitive tasks, and limited working memory capacity is thought to negatively affect performance on so many tasks. However, one area that does seem to have had some success is working memory training for those with ADHD, and researchers have certainly not given hope of finding evidence for wider transfer among other groups (such as older adults).

A recent review of the research to date has, sadly, concluded that the benefits of working memory training programs are limited. But this is not to say there are no benefits.

For a start, the meta-analysis (analyzing data across studies) found that working memory training produced large immediate benefits for verbal working memory. These benefits were greatest for children below the age of 10.

These benefits, however, were not maintained long-term (at an average of 9 months after training, there were no significant benefits) — although benefits were found in one study in which the verbal working memory task was very similar to the training task (indicating that the specific skill practiced did maintain some improvement long-term).

Visuospatial working memory also showed immediate benefits, and these did not vary across age groups. One factor that did make a difference was type of training: the CogMed training program produced greater improvement than the researcher-developed programs (the studies included 7 that used CogMed, 2 that used Jungle Memory, 2 Cognifit, 4 n-back, 1 Memory Booster, and 7 researcher-developed programs).

Interestingly, visuospatial working memory did show some long-term benefits, although it should be noted that the average follow-up was distinctly shorter than that for verbal working memory tasks (an average of 5 months post-training).

The burning question, of course, is how well this training transferred to dissimilar tasks. Here the evidence seems sadly clear — those using untreated control groups tended to find such transfer; those using treated control groups never did. Similarly, nonrandomized studies tended to find far transfer, but randomized studies did not.

In other words, when studies were properly designed (randomized trials with a control group that is given alternative treatment rather than no treatment), there was no evidence of transfer effects from working memory training to nonverbal ability. Moreover, even when found, these effects were only present immediately and not on follow-up.

Neither was there any evidence of transfer effects, either immediate or delayed, on verbal ability, word reading, or arithmetic. There was a small to moderate effect on training on attention (as measured by the Stroop test), but this only occurred immediately, and not on follow-up.

It seems clear from this review that there are few good, methodologically sound studies on this subject. But three very important caveats should be noted in connection with the researchers’ dispiriting conclusion.

First of all, because this is an analysis across all data, important differences between groups or individuals may be concealed. This is a common criticism of meta-analysis, and the researchers do try and answer it. Nevertheless, I think it is still a very real issue, especially in light of evidence that the benefit of training may depend on whether the challenge of the training is at the right level for the individual.

On the other hand, another recent study, that compared young adults who received 20 sessions of training on a dual n-back task or a visual search program, or received no training at all, did look for an individual-differences effect, and failed to find it. Participants were tested repeatedly on their fluid intelligence, multitasking ability, working memory capacity, crystallized intelligence, and perceptual speed. Although those taking part in the training programs improved their performance on the tasks they practiced, there was no transfer to any of the cognitive measures. When participants were analyzed separately on the basis of their improvement during training, there was still no evidence of transfer to broader cognitive abilities.

The second important challenge comes from the lack of skill consolidation — having a short training program followed by months of not practicing the skill is not something any of us would expect to produce long-term benefits.

The third point concerns a recent finding that multi-domain cognitive training produces longer-lasting benefits than single-domain training (the same study also showed the benefit of booster training). It seems quite likely that working memory training is a valuable part of a training program that also includes practice in real-world tasks that incorporate working memory.

I should emphasize that these results only apply to ‘normal’ children and adults. The question of training benefits for those with attention difficulties or early Alzheimer’s is a completely different issue. But for these healthy individuals, it has to be said that the weight of the evidence is against working memory training producing more general cognitive improvement. Nevertheless, I think it’s probably an important part of a cognitive training program — as long as the emphasis is on part.

We know that we remember more 12 hours after learning if we have slept during that 12 hours rather than been awake throughout, but is this because sleep is actively helping us remember, or because being awake makes it harder to remember (because of interference and over-writing from other experiences). A new study aimed to disentangle these effects.

In the study, 207 students were randomly assigned to study 40 related or unrelated word pairs at 9 a.m. or 9 p.m., returning for testing either 30 minutes, 12 hours or 24 hours later.

As expected, at the 12-hour retest, those who had had a night’s sleep (Evening group) remembered more than those who had spent the 12 hours awake (Morning group). But this result was because memory for unrelated word pairs had deteriorated badly during 12 hours of wakefulness; performance on the related pairs was the same for the two groups. Performance on the related and unrelated pairs was the same for those who slept.

For those tested at 24 hours (participants from both groups having received both a full night of sleep and a full day of wakefulness), those in the Evening group (who had slept before experiencing a full day’s wakefulness) remembered significantly more than the Morning group. Specifically, the Evening group showed a very slight improvement over training, while the Morning group showed a pronounced deterioration.

This time, both groups showed a difference for related versus unrelated pairs: the Evening group showed some deterioration for unrelated pairs and a slightly larger improvement for related pairs; the Morning group showed a very small deterioration for related pairs and a much greater one for unrelated pairs. The difference between recall of related pairs and recall of unrelated pairs was, however, about the same for both groups.

In other words, unrelated pairs are just that much harder to learn than related ones (which we already know) — over time, learning them just before sleep vs learning early in the day doesn’t make any difference to that essential truth. But the former strategy will produce better learning for both types of information.

A comparison of the 12-hour and 24-hour results (this is the bit that will help us disentangle the effects of sleep and wakefulness) reveals that twice as much forgetting of unrelated pairs occurred during wakefulness in the first 12 hours, compared to wakefulness in the second 12 hours (after sleep), and 3.4 times more forgetting of related pairs (although this didn’t reach significance, the amount of forgetting being so much smaller).

In other words, sleep appears to slow the rate of forgetting that will occur when you are next awake; it stabilizes and thus protects the memories. But the amount of forgetting that occurred during sleep was the same for both word types, and the same whether that sleep occurred in the first 12 hours or the second.

Participants in the Morning and Evening groups took a similar number of training trials to reach criterion (60% correct), and there was no difference in the time it took to learn unrelated compared to related word pairs.

It’s worth noting that there was no difference between the two groups, or for the type of word pair, at the 30-minutes test either. In other words, your ability to remember something shortly after learning it is not a good guide for whether you have learned it ‘properly’, i.e., as an enduring memory.

The study tells us that the different types of information are differentially affected by wakefulness, that is, perhaps, they are more easily interfered with. This is encouraging, because semantically related information is far more common than unrelated information! But this may well serve as a reminder that integrating new material — making sure it is well understood and embedded into your existing database — is vital for effective learning.

The findings also confirm earlier evidence that running through any information (or skills) you want to learn just before going to bed is a good idea — and this is especially true if you are trying to learn information that is more arbitrary or less well understood (i.e., the sort of information for which you are likely to use mnemonic strategies, or, horror of horrors, rote repetition).

Data from the very large and long-running Cognitive Function and Ageing Study, a U.K. study involving 13,004 older adults (65+), from which 329 brains are now available for analysis, has found that cognitive lifestyle score (CLS) had no effect on Alzheimer’s pathology. Characteristics typical of Alzheimer’s, such as plaques, neurofibrillary tangles, and hippocampal atrophy, were similar in all CLS groups.

However, while cognitive lifestyle may have no effect on the development of Alzheimer's pathology, that is not to say it has no effect on the brain. In men, an active cognitive lifestyle was associated with less microvascular disease. In particular, the high CLS group showed an 80% relative reduction in deep white matter lesions. These associations remained after taking into account cardiovascular risk factors and APOE status.

This association was not found in women. However, women in the high CLS group tended to have greater brain weight.

In both genders, high CLS was associated with greater neuronal density and cortical thickness in Brodmann area 9 in the prefrontal lobe (but not, interestingly, in the hippocampus).

Cognitive lifestyle score is produced from years of education, occupational complexity coded according to social class and socioeconomic grouping, and social engagement based on frequency of contact with relatives, neighbors, and social events.

The findings provide more support for the ‘cognitive reserve’ theory, and shed some light on the mechanism, which appears to be rather different than we imagined. It may be that the changes in the prefrontal lobe (that we expected to see in the hippocampus) are a sign that greater cognitive activity helps you develop compensatory networks, rather than building up established ones. This would be consistent with research suggesting that older adults who maintain their cognitive fitness do so by developing new strategies that involve different regions, compensating for failing regions.