Sleep and memory - round-up of recent reports

July, 2011

A round-up of recent reports relating to the role of sleep in consolidating memory.

Sleep can boost classroom performance of college students

There’s a lot of evidence that memories are consolidated during sleep, but most of it has involved skill learning. A new study extends the findings to complex declarative information — specifically, information from a lecture on microeconomics.

The study involved 102 university undergraduates who had never taken an economics course. In the morning or evening they completed an introductory, virtual lecture that taught them about concepts and problems related to supply and demand microeconomics. They were then tested on the material either immediately, after a 12-hour period that included sleep, after 12 hours without sleep, or after one week. The test included both basic problems that they had been trained to solve, and "transfer" problems that required them to extend their knowledge to novel, but related, problems.

Performance was better for those who slept, and this was especially so for the novel, 'transfer' integration problems.

Rule-learning task also benefits from sleep

Another complex cognitive task was investigated in a study of 54 college undergraduates who were taught to play a card game for rewards of play money in which wins and losses for various card decks mimic casino gambling (the Iowa Gambling Task is typically used to assess frontal lobe function). Those who had a normal night’s sleep as part of the study drew from decks that gave them the greatest winnings four times more often than those who spent the 12-hour break awake, and they better understood the underlying rules of the game.

The students were given a brief morning or afternoon preview of the gambling task (too brief to learn the underlying rule). They returned twelve hours later (i.e., either after a normal night’s sleep, or after a day of their usual activities), when they played the full gambling task for long enough to learn the rules. Those who got to sleep between the two sessions played better and showed a better understanding of the rules when questioned.

To assure that time of day didn’t explain the different performance, two groups of 17 and 21 subjects carried out both the preview and the full task either in the morning or the evening. Time of day made no difference.

Sleep problems may be a link between perceived racism and poor health

Analysis of data from the 2006 Behavioral Risk Factor Surveillance System, involving 7,093 people in Michigan and Wisconsin, suggests that sleep deprivation may be one mediator of the oft-reported association between discrimination and poorer cognitive performance.

The survey asked the question: "Within the past 12 months when seeking health care, do you feel your experiences were worse than, the same as, or better than for people of other races?" Taking this as an index of perceived racism, and comparing it with reports of sleep disturbance (difficulty sleeping at least six nights in the past two weeks), the study found that individuals who perceived racial discrimination were significantly more likely to experience sleep difficulties, even after allowing for socioeconomic factors and depression. Risk of sleep disturbance was nearly doubled in those who perceived themselves as discriminated against, and although this was reduced after depression was taken into account, it remained significant.

Sleep problems more prevalent than expected in urban minority children

Ten families also underwent sleep monitoring at home for five to seven days. All children who completed actigraphy monitoring had shortened sleep duration, with an average sleep duration of 8 hours, significantly less than the 10 to 11 hours recommended for children in this age group.

It’s worth noting that parents consistently overestimated sleep duration. Although very aware of bedtime and wake time, parents are less aware of time spent awake during the night.

(Also note that the figures I quote are taken from the conference abstract, which differ from those quoted in the press release.)

Rocking really does help sleep

If you or your loved one is having troubles getting to sleep, you might like to note an intriguing little study involving 12 healthy males (aged 22-38, and good sleepers). The men twice took a 45-minute afternoon nap on a bed that could slowly rock. On one occasion, it was still; on the other, it rocked. Rocking brought about faster sleep, faster transition to deeper sleep, and increased slow oscillations and sleep spindles (hallmarks of deep sleep). All these results were evident in every participant.

Sleep helps long-term memory in two ways

A fruit fly study points to two dominant theories of sleep being correct. The two theories are (a) that synapses are pruned during sleep, ensuring that only the strongest connections survive (synaptic homeostasis), and (b) that memories are replayed and consolidated during sleep, so that some connections are reactivated and thus made stronger (memory consolidation).

The experiment was made possible by the development of a new strain of fruit fly that can be induced to fall asleep when temperatures rise. The synaptic homeostasis model was supported when flies were placed in socially enriched environments, then either induced to sleep or not, before being taught a courtship ritual. Those that slept developed long-term memories of the ritual, while those that didn’t sleep didn’t remember it. The memory consolidation theory was supported when flies trained using a protocol designed to give them short-term memories retained a lasting memory, if sleep was induced immediately after the training.

In other words, it seems that both pruning and replaying are important for building long-term memories.

Mouse studies identify the roots of memory impairment resulting from sleep deprivation

Sleep deprivation in known to result in increased levels of adenosine in the brain, whether fruit fly or human (caffeine blocks the effects of adenosine). New mice studies now reveal the mechanism.

Mice given a drug that blocked a particular adenosine receptor in the hippocampus (the A1 receptor) failed to show the normal memory impairment evoked by sleep deprivation (being woken halfway through their normal 12-hour sleep schedule). The same results occurred if mice were genetically engineered to lack a gene involved in the production of glial transmitters (necessary to produce adenosine).

Memory was tested by the mice being allowed to explore a box with two objects, and then returned to the box on the next day, where one of the two objects had been moved. They would normally explore the moved object more than other objects, but sleep-deprived mice don’t usually react to the change, because they don’t remember where the object had been. In both these cases, the sleep-deprived mice showed no memory impairment.

Both the drugged and genetically protected mice also showed greater synaptic plasticity in the hippocampus after being sleep deprived than the untreated group.

The two groups reveal two parts of the chemical pathway involved in sleep deprivation. The genetic engineering experiment shows that the adenosine comes from glia's release of adenosine triphosphate (ATP). The drug experiment shows that the adenosine goes to the A1 receptor in the hippocampus.

The findings provide the first evidence that astrocytic ATP and adenosine A1R activity contribute to the effects of sleep deprivation on hippocampal synaptic plasticity and hippocampus-dependent memory, and suggest a new therapeutic target to reverse the cognitive deficits induced by sleep loss.

 

Reference: 

Scullin M, McDaniel M, Howard D, Kudelka C. 2011. Sleep and testing promote conceptual learning of classroom materials.  Presented Tuesday, June 14, in Minneapolis, Minn., at SLEEP 2011, the 25th Anniversary Meeting of the Associated Professional Sleep Societies LLC (APSS).

[2297] Pace‐Schott, E. F., Nave G., Morgan A., & Spencer R. M. C. (Submitted).  Sleep‐dependent modulation of affectively guided decision‐making. Journal of Sleep Research.

Grandner MA, Hale L, Jackson NJ, Patel NP, Gooneratne N, Troxel WM. 2011. Sleep disturbance and daytime fatigue associated with perceived racial discrimination. Presented Tuesday, June 14, in Minneapolis, Minn., at SLEEP 2011, the 25th Anniversary Meeting of the Associated Professional Sleep Societies LLC (APSS).

Sheares, B.J., Dorsey, K.B., Lamm, C.I., Wei, Y., Kattan, M., Mellins, R.B. & Evans, D. 2011. Sleep Problems In Urban Minority Children May Be More Prevalent Than Previously Recognized. Presented at the ATS 2011 International Conference in Denver.

[2330] Bayer, L., Constantinescu I., Perrig S., Vienne J., Vidal P. - P., Mühlethaler M., et al. (2011).  Rocking synchronizes brain waves during a short nap. Current Biology. 21(12), R461-R462 - R461-R462.

[2331] Donlea, J. M., Thimgan M. S., Suzuki Y., Gottschalk L., & Shaw P. J. (2011).  Inducing Sleep by Remote Control Facilitates Memory Consolidation in Drosophila. Science. 332(6037), 1571 - 1576.

[2287] Florian, C., Vecsey C. G., Halassa M. M., Haydon P. G., & Abel T. (2011).  Astrocyte-Derived Adenosine and A1 Receptor Activity Contribute to Sleep Loss-Induced Deficits in Hippocampal Synaptic Plasticity and Memory in Mice. The Journal of Neuroscience. 31(19), 6956 - 6962.

Source: 

Sleep can boost classroom performance of college students
http://www.eurekalert.org/pub_releases/2011-06/aaos-scb060611.php
Rule-learning task also benefits from sleep
http://medicalxpress.com/news/2011-05-excellent-science-based-advice.html
Sleep problems may be a link between perceived racism and poor health
http://medicalxpress.com/news/2011-06-problems-link-racism-poor-health.html
Sleep problems more prevalent than expected in urban minority children
http://medicalxpress.com/news/2011-05-problems-prevalent-urban-minority-...
Rocking really does help sleep
http://www.scientificamerican.com/podcast/episode.cfm?id=rocking-increas...
Sleep helps long-term memory in two ways
http://the-scientist.com/2011/06/23/sleep-on-it/
Mouse studies identify the roots of memory impairment resulting from sleep deprivation
http://www.eurekalert.org/pub_releases/2011-05/uop-pri051711.php

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