The role of sleep in memory: Research reports

What sleep does for memory

February 2008

A nap can help you learn

A study of 33 younger adults (average are 23) has found that a 45 minute afternoon nap (containing only non-REM sleep) improved performance on 3 different declarative memory tasks, but only when the subjects had reached a certain level of performance during training.
The study was published in the February 1 issue of SLEEP. Full reference
http://www.eurekalert.org/pub_releases/2008-02/aaos-jss012808.php

January 2008

Brain connections strengthen during waking hours, weaken during sleep

New research provides support for a much-debated theory that we need sleep to give our synapses time to rest and recover. The human brain is said to expend up to 80% of its energy on synaptic activity, constantly adding and strengthening connections in response to stimulation. The researchers have theorized that we need an ‘off-line period’, when we are not exposed to the environment, to take synapses down. The rodent study has revealed by several measures that synapses — the all-important points of connection between neurons — are very active when the animal is awake and very quiet during sleep. The researchers feel that these findings support the idea that our brain circuits get progressively stronger during wakefulness and that sleep helps to recalibrate them to a sustainable baseline. This theory is of course opposite to the currently dominant hypothesis, that during sleep synapses are hard at work replaying the information acquired during the previous waking hours, consolidating that information by becoming even stronger.
The report appeared online January 20 in Nature Neuroscience. Full reference
http://www.physorg.com/news120059987.html

April 2007

Sleep reinforces the temporal sequence in memory

Following on from research showing long-term memory is consolidated during sleep through the replaying of recently encoded experiences, a study has found that the particular order in which they were experienced is also strengthened, probably by a replay of the experiences in "forward" direction. The study involved students being asked to learn triplets of words presented one after the other. Those whose recall of the order of the words was tested after sleep showed better recall, but only when they were asked to reproduce the learned words in forward direction.
The paper appeared in the April 18 issue of PLoS ONE. Full reference
http://www.eurekalert.org/pub_releases/2007-04/plos-set041707.htm

Sleep protects against interference

A study involving 48 people (aged 18—30) found that those who learned 20 pairs of words at 9pm and were tested at 9am the following morning, after a night’s sleep, performed better than those who learned them at 9am and were tested at 9pm of the same day. Moreover, for those who were given a second list of word pairs to remember just before testing, where the first word in each pair was the same as on the earlier list, the advantage of sleep was dramatically better. For those who experienced the interference manipulation, those in the sleep group recalled 12% more word pairs than the wake group, but with interference, the recall rate was 44% higher for the sleep group.
The findings were presented by Dr Jeffrey Ellenbogen at the American Academy of Neurology’s 59th Annual Meeting in Boston, April 28 – May 5, 2007.
http://www.eurekalert.org/pub_releases/2007-04/aaon-ssy040307.htm

Sleeping helps us put facts together

And in yet another sleep study, researchers found evidence that sleep also helps us see the big picture. The study involved 56 students who were shown oval images of colorful abstract patterns nicknamed "Fabergé eggs." Participants were first shown a combination of five pairs of the eggs, all of which were given ratings. The students were given 30 minutes to learn which shape rated higher and so should be chosen over another shape. They were not told the hidden connection that linked all five pairs together. They were then tested either after 20 minutes, after 12 hours, or after 24 hours. Half of those in the 12-hour group slept before the test, the other half did not. The 20-minute group performed the worst, showing no evidence of seeing the pattern. Those who had longer before being tested were much more likely to show signs of inferential judgment (75% vs 52%), and for the most distant (and difficult) inferential judgment, the students who had had periods of sleep in between learning and testing significantly outperformed those who hadn’t slept (93% vs 69%). The researchers are interested in exploring whether meditation can provide a similar benefit.
The findings appeared online April 20 in the Early Edition of the Proceedings of the National Academy of Sciences. Full reference
http://www.physorg.com/news98376198.html
http://www.eurekalert.org/pub_releases/2007-04/bidm-tut042007.htm

More on how memories are consolidated during sleep

A new study sheds more light on how memory is consolidated during sleep. Using a new technique, the research confirms that new information is transferred between the hippocampus and the cerebral cortex, and, unexpectedly, provides evidence suggesting that the cerebral cortex actively controls this transfer.
The study appeared in the November issue of Nature Neuroscience. Full reference
http://www.eurekalert.org/pub_releases/2006-12/m-lds120506.htm

Still more on how memories are consolidated during sleep

In research following up an earlier study in which rats were shown to form complex memories for sequences of events experienced while they were awake, and that these memories were replayed while they slept, it has been shown that these replayed memories do contain the visual images that were present during the running experience. By showing that the brain is replaying memory events in the visual cortex and in the hippocampus at the same time, the finding suggests that this process may contribute to or reflect the result of the memory consolidation process.
The report appeared December 17 in the advance online edition of Nature Neuroscience. Full reference
http://www.eurekalert.org/pub_releases/2006-12/miot-mtr121806.htm

October 2007

Brainwave oscillations responsible for memory benefits of sleep?

Passing a mild electrical current through the brain while students were asleep improved their ability to remember words on waking up. 13 medical students were given 46 pairs of words to learn. Before sleeping, they remembered an average 37.42 words; after sleep, those not given the stimulation remembered an average of 39.5, while those given the stimulation remembered an average of 41.27. The memory enhancement only occurred at a certain frequency and during a particular part of the sleep cycle, confirming the idea that slow oscillations of electrical activity are responsible for the memory consolidation effects of sleep. The benefit also only applied to fact learning; skill learning was not affected.
The results were published online 5 November in Nature. Full reference
http://www.guardian.co.uk/science/story/0,,1940475,00.html
http://www.sciam.com/article.cfm?chanID=sa003&articleID=BEC346B2-E7F2-99DF-350CC33BA6757700
http://www.nature.com/news/2006/061030/full/444133a.html

September 2006

More support that sleep helps consolidate learning

An experiment involving fruitflies has found that those in a social environment with at least 30 other flies slept four times as long during their daytime naps as flies in isolation. There was no difference in night-time sleep. The length of the nap increased with the size of the group they socialized with. Confirming that this effect was due to an increase in social interactions, rather than, for example, physical exhaustion from flying around more, flies deprived of their sight and sense of smell (meaning they could still fly around but could not socialize) showed no difference in daytime sleep patterns. Of 49 genes known to be involved in learning and memory, switching off seventeen (all related to long-term memory) made the flies sleep equally long regardless of whether they were social or not.
The study was reported in the September 22 issue of Science. Full reference
http://www.nature.com/news/2006/060918/full/060918-9.html
http://www.livescience.com/humanbiology/060921_flies_sleep.html

Human study supports value of daytime napping for learning

REM sleep, when most dreaming occurs, has been shown in a number of studies to be important in consolidating procedural (skill) learning, while non-REM (slow-wave) sleep seems to be more important for declarative (knowledge-based) learning. However, because normal sleep contains both REM and non-REM cycles, research hasn’t been able to clearly distinguish the effects. Now a new study using brief daytime napping confirms the role of non-REM sleep for declarative learning. Volunteers who memorized pairs of words and practiced tracing images in a mirror test scored 15% better in the word test if they had been allowed a nap in the six hour period before being tested. However, they did no better at the action test.
The report appeared in the September issue of Neurobiology of Learning and Memory. Full reference
http://www.newscientist.com/article/mg19125704.800?DCMP=NLC-nletter&nsref=mg19125704.800

July 2006

Sleep makes memories resistant to interference

It’s pretty clear now that sleep consolidates procedural (skill) learning, but the question of whether or not it helps other types of memory is still very much a matter of debate. However, a new study has found a marked effect of sleep on our ability to remember information. The study involved 60 healthy college-aged adults, who were asked them to memorize 20 pairs of random words. Half were given the words at 9am and tested at 9pm, and the other half were given the words at 9pm and tested at 9am. While the sleepers did perform better (94% recall compared to 82%), it was the introduction of another factor that made the benefits of sleep undeniable. Participants who were given a new set of words to learn just 12 minutes before testing revealed a dramatic difference — sleepers recalled 76% of the original words compared to 32% of the sleepless.
The findings are reported in the July 12 issue of Current Biology. Full reference
http://www.sciencedaily.com/releases/2006/07/060711095912.htm
http://www.sciam.com/article.cfm?chanID=sa003&articleID=0006A257-BBB4-14B2-B8B983414B7F4945

March 2006

Asleep or awake we retain memory

We’ve learned that skill memory is reinforced during sleep, but now new imaging technology reveals that this kind of reinforcement occurs while we’re awake too — even while we’re learning something new.
The study was published in PLoS Biology. Full reference
http://www.eurekalert.org/pub_releases/2006-03/plos-aoa032206.htm
http://www.sciencedaily.com/releases/2006/03/060329085308.htm

June 2005

How sleep improves memory

While previous research has been conflicting, it does now seem clear that sleep consolidates learning of motor skills in particular. A new imaging study involving 12 young adults taught a sequence of skilled finger movements has found a dramatic shift in activity pattern when doing the task in those who were allowed to sleep during the 12 hour period before testing. Increased activity was found in the right primary motor cortex, medial prefrontal lobe, hippocampus and left cerebellum — this is assumed to support faster and more accurate motor output. Decreased activity was found in the parietal cortices, the left insular cortex, temporal pole and fronto-polar region — these are assumed to reflect less anxiety and a reduced need for conscious spatial monitoring. It’s suggested that this is one reason why infants need so much sleep — motor skill learning is a high priority at this age. The findings may also have implications for stroke patients and others who have suffered brain injuries.
The findings were reported in the June 30 issue of Neuroscience. Full reference http://www.eurekalert.org/pub_releases/2005-06/bidm-ssh062805.htm

October 2004

More evidence that learning is consolidated during sleep

A new study provides more evidence for the role of sleep in the consolidation of long-term memories. In the study, volunteers learned the layout of a virtual town, and were then tested by having to quickly find routes to various locations in the town. Those so trained showed greater activity in their hippocampus and an adjacent learning-related region (compared to those not trained) as they took the route tests, with greater activity correlated with better performance. They also showed greater hippocampal brain activity during sleep. Most importantly, the higher the gain in post-sleep performance on the tests, the higher had been their NREM brain activity during sleep. No such correlation was found in REM brain activity. The findings support the view that spatial memory traces are processed during NREM sleep in humans.
The study appeared in the October 28 issue of Neuron. Full reference
http://www.eurekalert.org/pub_releases/2004-10/cp-etl102204.htm

February 2004

Mentally, sleep may be as active a state as waking state

Why do we sleep? A question we keep asking. Recent research leads us another step in the road. The study has identified a number of genes upregulated specifically during sleep – at least as many as are turned on while we are awake. These "sleep genes" largely fall into four categories: genes involved in synaptic plasticity (supporting the view that sleep aids memory consolidation); genes underlying translation (supporting observations that protein synthesis increases during sleep); genes regulating membrane and vesicle trafficking; and genes for synthesizing cholesterol (which may be crucial for synapse formation and maintenance, which could, in turn, enhance neural plasticity (the brain's ability to change and learn)). The study also found, to the researchers’ surprise, that the cerebellum showed largely the same pattern of gene-expression during sleep as the cortex.
The study was published in the January 8 issue of Neuron. Full reference
http://www.the-scientist.com/yr2004/feb/research2_040216.html

More on what goes on during sleep

Brain activity patterns vary during sleep, with particular distinction being made between “REM” sleep and “deep” sleep. Both these phases of sleep have been associated with memory processing. The chemical composition of the brain also varies a great deal in the sleep and wakefulness cycle. New research from Germany now report that some of these differences are crucial in memory formation during sleep. In particular, the level of acetylcholine (a neurotransmitter) is high during wakefulness and REM sleep but drops to the minimum in deep sleep. In an experiment that involved subjects performing two memory tasks – learning 40 pairs of semantically related words, and learning to trace figures seen in a mirror – before sleeping for four hours, it was found that those who were given a cholinesterase inhibitor, (cholinesterase being an enzyme that breaks down acetylcholine), performed significantly less well in the wordlist task on wakening. The mirror-tracing task didn't seem to be affected. This supports the idea that a low level of acetylcholine is necessary for strengthening explicit memory during deep sleep, and fits in with a proposed two-stage model of long-term memory formation, in which the cortex transfers newly acquired experiential data to the hippocampus for processing and temporary storage (a process requiring high levels of acetylcholine), and then, during sleep, the processed memory traces in the hippocampus are relayed back to the cortex for long-term storage. This feedback process is blocked by acetylcholine and, thus, only happens in sleep when the acetylcholine level drops to the minimum.
The research may also have important implications for treating memory loss associated with Alzheimer's disease, as cholinesterase inhibitors are widely used in such treatment. Because of common side-effects of the drug, patients are usually told to take it at night, which may well weaken the drug’s effectiveness.
The study was published in the February 17 issue of Proceedings of National Academy of Sciences. Full reference
http://gateways.bmn.com/neuroscience/news?uid=NEWS.040219-1

January 2004

Now definite? Memories are consolidated during sleep

Researchers of a new study claim that their research finally settles the question of whether or not sleep consolidates new memories. The study involved detailed recording of specific learning- and memory- related areas (hippocampus and forebrain) in the brains of rats. The rats were exposed to four kinds of novel objects. Analysis of brain signals before, during, and after this experience, revealed "reverberations" of distinctive brain wave patterns across all the areas being monitored for up to 48 hours after the novel experience. This pattern was much more prevalent in slow-wave sleep than in REM sleep. Previous studies by the same researchers have found that the activation of genes that affect memory consolidation occurs during REM sleep, not slow-wave sleep. It is proposed that both stages of sleep are important for memory consolidation. Previous studies have tended to focus solely on the hippocampus, and have observed brain activity for a much shorter period.
The researchers published their findings on Jan. 19, 2004, in the online Public Library of Science. Full reference
http://www.eurekalert.org/pub_releases/2004-01/dumc-etm011304.htm
http://www.eurekalert.org/pub_releases/2004-01/plos-brd011204.htm
http://www.plosbiology.org/plosonline/?request=get-document&doi=10.1371/journal.pbio.0020037
Full text: http://www.plosbiology.org/plosonline/?request=get-document&doi=10.1371%2Fjournal.pbio.0020024

Sleep helps insight

A new German study provides evidence for what we all suspected — “sleeping on” a problem can really work. In the study, participants were given a mathematical puzzle to solve; a puzzle which could be solved by trial-by-trial learning, or almost immediately if participants grasped the hidden rule. After training in the trial-by-trial learning, some of the participants were allowed to sleep through the night, while others were prevented from sleeping. When they returned to the problem eight hours later, those that had slept were twice as likely to realize the rule. Another group that trained in the morning, and were then tested later that day, were also slower at finding the rule, suggesting that the slowness was not solely due to fatigue. Sleep did not, however, help participants who had not had the initial training. It is suggested that sleep can act to restructure new memory representations.
The study was published on 22 January in Nature. Full reference
http://www.sciam.com/article.cfm?chanID=sa003&articleID=000088CE-E9DC-100E-A9DC83414B7F0000
http://www.sfgate.com/cgi-bin/article.cgi?file=/news/archive/2004/01/21/national0259EST0431.DTL
http://www.nature.com/nsu/040119/040119-10.html
http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v427/n6972/abs/nature02223_fs.html

October 2003

Stages of memory clarified in sleep studies

Two new studies add to our understanding of the effects of sleep on memory. Both studies involved young adults and procedural (skill) learning, and found temporary declines in performance in particular contexts (a brief description of these studies is given here). On the basis of these studies, researchers identified three stages of memory processing: the first stage of memory — its stabilization — seems to take around six hours. During this period, the memory appears particularly vulnerable to being “lost”. The second stage of memory processing — consolidation — occurs during sleep. The third and final stage is the recall phase, when the memory is once again ready to be accessed and re-edited. (see my article on consolidation for more explanation of the processes of consolidation and re-consolidation). The surprising aspect to this is the time it appears to take for memories to initially stabilize. The studies also confirm the role of sleep in the consolidation process.
The studies appeared in the October 9 issue of Nature. Full reference 2
http://www.eurekalert.org/pub_releases/2003-10/bidm-som100703.htm
http://www.sciencenews.org/20031011/fob4.asp
http://education.guardian.co.uk/higher/research/story/0,9865,1059138,00.html

July 2003

More support for the theory that sleep is necessary to consolidate memories

A study used fear conditioning in mice to investigate the effect of sleep deprivation on memory. The mice were given a mild electric shock either in a distinctive setting, or subsequent to a tone. Those who experienced the tone continued to freeze when they heard the tone on the following day, whether or not they had been deprived of sleep. Those who associated the environment with the shock, however, were less likely to freeze after sleep deprivation. Mice who had been deprived of sleep during the five hours following training, spent just 4% of their time frozen when returned to the ‘shock environment’ the following day, compared to 15% among mice who were allowed to sleep during this period. The five hours following training was a critical period – those who were deprived of sleep in the 5-10 hours after training showed no sign of memory impairment. The fact that the context association was affected but not the tone cue, suggests that sleep is affecting processes in the hippocampus (important in context memory but not memory for specific facts or events).
The results were reported in the May/June issue of Learning & Memory. Full reference
http://www.eurekalert.org/pub_releases/2003-07/uop-sdw070803.htm

June 2003

Another step in understanding how sleep affects memory

The value of sleep for memory takes a further step in being understood in new rodent research, which found that, as the rodents slept, the thalamus at the base of their brains originated bursts of electrical activity (“sleep spindles”), which were then detected in the somatosensory neocortex. Some 50 msec later, the hippocampus responded with a pulse of electricity (a “ripple”). "This neocortical-hippocampal dialogue may provide a selection mechanism for the time-compressed replay of information learned during the day." It’s suggested that the ripple is the hippocampus sending back neat, compact waves of memory to the neocortex where they are filed away for future reference. Most of this activity took place during slow wave sleep, the stage which makes up the majority of the sleep cycle.
The findings are reported in the June 6 issue of Science. Full reference
http://www.eurekalert.org/pub_releases/2003-06/nyu-fir060503.htm
http://tinyurl.com/ftob

July 2002

Napping reverses information overload

Evidence is mounting that sleep helps information processing and learning. A new study has showed that subjects performing a visual task (reporting the horizontal or vertical orientation of three diagonal bars against a background of horizontal bars in the corner of a computer screen) got worse over the course of four daily practice sessions. However, allowing subjects a 30-minute nap after the second session prevented any further deterioration, and a 1-hour nap actually boosted performance in the third and fourth sessions back to morning levels. It appears that the fatigue is limited to the brain visual system circuits involved in the task. When the image was switched to a different right corner of the computer screen on the fourth practice session, subjects performed about as well as they did in the first session -- or after a short nap. Recordings of brain activity reveal that the 1-hour naps contained more than four times as much deep, or slow wave sleep and rapid eye movement (REM) sleep than the half-hour naps.
The study was reported in the July 1 issue of Nature Neuroscience. Full reference
http://www.eurekalert.org/pub_releases/2002-07/niom-np070102.htm

Improving motor skills through sleep

People taught a simple motor sequence (to type a sequence of keys on a computer keyboard as quickly and accurately as possible) practised it for 12 minutes and were then re-tested 12 hours later. Those who practised in the morning and tested later that same day improved their performance by about 2%. Those trained in the evening and re-tested after a good night's sleep, however, improved by about 20%. The amount of improvement was directly correlated with the amount of Stage 2 (a stage of non-rapid eye movement or NREM) sleep experienced, particularly late in the night. "This is the part of a good night's sleep that many people will cut short by getting up early in the morning."
The study appeared in the July 3 issue of Neuron. Full reference
http://www.eurekalert.org/pub_releases/2002-07/hms-pmp070102.htm

November 2001

Controversy over sleep's role in memory

Does sleep play a role in memory or not? Two new research papers reach opposite conclusions. One is from Robert Stickgold, who has published several papers supporting the role of sleep in memory consolidation. But the other is a new review of REM sleep studies concluding that REM (rapid eye movement) sleep, or dreaming, plays little role in memory formation, chiefly on the basis that depriving animals and humans of REM sleep by awakening them or by drug treatments does not impair their ability to form long-term memories. In addition, the time spent in REM sleep does not correlate with learning ability across humans, nor is there a positive relation between amount or intensity of REM sleep and learning ability across species.
The articles appear in the November 2 edition of Science. Full references
1, 2
http://www.sciencemag.org/cgi/content/abstract/294/5544/1052
http://www.sciencemag.org/cgi/content/abstract/294/5544/1058

October 2001

New motor skills consolidated during sleep

An imaging study that sheds light on the gain in performance observed during the day after learning a new task. Following training in a motor skill, certain brain areas appear to be reactived during REM sleep, resulting in an optimization of the network that subtends the subject's visuo–motor response.
The report appeared in the October issue of Neuroscience. Full reference

November 2000

Deep "slow wave" sleep necessary to consolidate memories

Sleep is necessary to consolidate memories. Remembering a new task is more difficult if you don't sleep within 30 hours of learning the task. "Catch-up" sleep on subsequent nights doesn't make up for losing that first night's sleep. Moreover, it appears that the deep "slow wave" sleep that occurs in the first half of the night is the type of sleep necessary to consolidate memories. Other types of memory however, may require "REM" sleep (that occurs while you are dreaming).
The study was published in the December issue of Nature Neuroscience.
http://www.independent.co.uk/story.jsp?story=6296

Stickgold, R., James, L. & Hobson, J.A. 2000. Visual discrimination learning requires sleep after training. Nature Neuroscience,3, 1237-1238.

Sleep deprivation & apnea

February 2008

REM sleep deprivation reduces neurogenesis

And in another sleep study, rats deprived of REM sleep for four days showed reduced cell proliferation in the dentate gyrus of the hippocampus, where most adult neurogenesis takes place. The finding indicates that REM sleep is important for brain plasticity.
The study was published in the February 1 issue of SLEEP. Full reference
http://www.eurekalert.org/pub_releases/2008-02/aaos-fdo012808.php

September 2007

Insufficient sleep in early childhood associated with developmental delay

A long-term study of nearly 1500 young children (from 5 months to six years) found four sleep duration patterns; 6% slept less than 10 hours per night throughout early childhood, and 4.8% did so until around 41 months, when it increased. Short sleep duration was found to significantly increase the risk of low performance on the Peabody Picture Vocabulary Test–Revised (given at 5 years), suggesting that language acquisition and the consolidation of new words into memory could be significantly impeded by chronically shortened sleep duration throughout childhood. An increased risk of poorer performance on the Block Design subtest (given at 6 years) was also evident even among those who had increased their sleep duration, suggesting that there is a critical period in early childhood where the lack of sleep is particularly detrimental on various aspects of development even if the sleep duration normalizes later on.
The study was published in the September 1 issue of SLEEP.    Full reference 
http://www.eurekalert.org/pub_releases/2007-09/aaos-jsl082407.php

July 2007

Memory problems and sleep disturbance linked in older women

A large long-running study, involving older women (average age 69) found that the nearly 25% of women who experienced cognitive decline over the 15 year period were twice as likely as women without memory problems to experience sleep disturbances, specifically problems staying asleep, and also problems falling asleep and being awake for more than 90 minutes during their sleep cycle. Women who declined on one of the two cognitive tests were also nearly twice as likely to nap more than two hours a day. However, cognitive decline was not associated with total sleep time. The association between sleep disturbances and poor cognitive function is of course well-known, but these findings raise the possibility that cognitive decline may increase the risk of sleep problems, rather than vice versa.
The study was published in the July 17 issue of Neurology. Full reference
http://www.eurekalert.org/pub_releases/2007-07/aaon-oww071007.php

February 2007

African-American and poor children more affected by sleep problems

A study involving 166 8- and 9-year-old African-American and European-American children from varying socioeconomic backgrounds has found that sleep disruption has greater effects on cognitive performance for children from lower-income homes and African-American children. When socioeconomic status was taken into consideration, African-American and European-American children's performance on cognitive tests was similar when they slept well. But when sleep was disrupted, African-American children's performance was worse. Similarly, children from lower and higher socioeconomic backgrounds performed similarly on tests when they slept well and their sleep schedules were consistent. But when their sleep was disrupted, children from higher-income homes did better than children from lower-income homes.
The study was published in the January/February 2007 issue of Child Development. Full reference
http://www.eurekalert.org/pub_releases/2007-02/sfri-csp013107.htm

January 2007

Sleep deprivation affects neurogenesis

A rat study has found that rats deprived of sleep for 72 hours had higher levels of the stress hormone corticosterone, and produced significantly fewer new brain cells in a particular region of the hippocampus. Preventing corticosterone levels from rising also prevented the reduction in neurogenesis.
The findings were reported in the December 12 issue of Proceedings of the National Academy of Science. Full reference
http://news.bbc.co.uk/2/hi/health/6347043.stm

December 2006

Memory improves after sleep apnea therapy

Patients with obstructive sleep apnea (OSA) often complain of forgetfulness. A study of 58 memory-impaired patients with clinically diagnosed OSA has found that 68% of those who used continuous positive airway pressure (CPAP) machines for an average of more than 6 hours a night regained normal memory after three months. Memory improvement varied based on CPAP adherence: 21% of poor users (fewer than 2 hours/night of CPAP use), 44% of moderate users (2 to 6 hours/night) demonstrated normal memory performance after three months. However, evidence suggests this optimal level of CPAP adherence is uncommon following 3 months of treatment.
The study was published in the December issue of CHEST. Full reference
http://www.eurekalert.org/pub_releases/2006-12/acoc-mia120606.htm

August 2006

Childhood sleep apnea linked to brain damage, lower IQ

It’s long been known that sleep apnea, characterized by fragmented sleep, interrupted breathing and oxygen deprivation, harms children's learning ability and school performance. Now a new study involving 19 children with severe obstructive sleep apnea has identified damage in the hippocampus and the right frontal cortex, and linked that to observable deficits in performance on cognitive tests. Children with OSA had an average IQ of 85 compared to 101 in matched controls. They also performed worse on standardized tests measuring executive functions, such as verbal working memory (8 versus 15) and word fluency (9.7 versus 12). Obstructive sleep apnea affects 2% of children in the United States, but it is unclear how many of these suffer from severe apnea.
The report appeared in the August 22 issue of Public Library of Science Medicine. Full reference
Full text available at:
http://medicine.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pmed.0030301
http://www.eurekalert.org/pub_releases/2006-08/jhmi-csa081506.htm

January 2006

Morning grogginess worse for cognition than sleep deprivation

People who awaken after eight hours of sound sleep have more impaired thinking and memory skills than they do after being deprived of sleep for more than 24 hours. The impairment is worst in the first three minutes, and the most severe effects have generally dissipated by ten minutes, but measurable effects can last up to two hours. This is consistent with reports indicating that cortical areas like the prefrontal cortex take longer to come “online” after sleep than other parts of the brain. The findings have implications for medical, safety and transportation workers who are often called upon to perform critical tasks immediately after waking, as well as for anyone abruptly woken to face an emergency situation.
The study appeared in the January 11 issue of the Journal of the American Medical Association. Full reference
http://www.eurekalert.org/pub_releases/2006-01/uoca-mgm121905.htm

January 2006

Losing sleep inhibits neurogenesis

A new sleep study using rats restricted rather than deprived them of sleep, to mimic more closely the normal human experience. The study found that the sleep-restricted rats had a harder time remembering a path through a maze compared to their rested counterparts. The sleep-restricted rats showed reduced survival rate of new hippocampus cells — learning spatial tasks increases the production of new cells in the hippocampus. This study shows that sleep plays a part in helping those new brain cells survive. However, the sleep-restricted rats that were forced to use visual and odor cues to remember their way through the maze did better on the task than their rested counterparts, implying that some types of learning don’t require sleep.
The study appeared in the December issue of the Journal of Neurophysiology. Full reference
http://www.eurekalert.org/pub_releases/2006-01/aps-lsu010506.htm

October 2004

Breathing problems during sleep may affect mental development in infants and young children

Two new studies have found evidence that children who have problems breathing during sleep tend to score lower on tests of mental development and intelligence than do other children their age. The first study found that at one year of age, infants who have multiple, brief breathing pauses (apnea) or slow heart rates during sleep scored lower on mental development tests than did other infants of the same age. The second study found that 5-year-old children who had frequent snoring, loud or noisy breathing during sleep, or sleep apneas observed by parents scored lower standard tests measuring executive function (attention and planning), memory, and general intelligence. More than 10 percent of young children have habitual snoring, the mildest form of sleep-disordered breathing (SDB). The effects of poor sleep are often overlooked or misinterpreted in children -- rather than appearing sleepy, children may in fact seem to be more active or even hyperactive.
Both studies appear in the October issue of Journal of Pediatrics. Full reference 2
http://www.eurekalert.org/pub_releases/2004-10/nhla-bpd100604.htm

May 2004

More on effects of sleep loss and fatigue on memory and learning

Just to confirm what we all know (I hope): a study of medical residents from five U.S. academic health centers has found that sleep loss and fatigue affect learning, job performance and personal relationships. Specifically, residents reported adverse effects on their abilities to learn, either in short-term or long-term memory of material; on their motivation to learn; and on their higher-order thinking skills (cognitive abilities and complex thinking).
The research paper appears in a special theme issue on medical residents in the May issue of Academic Medicine.
Full reference
http://www.eurekalert.org/pub_releases/2004-05/cwru-mrr050404.htm

November 2003

Sleep deprivation affects working memory

A recent study investigated the working memory capacities of individuals who were sleep-deprived. For nine days, 7 of the 12 participants slept four hours each night, and 5 slept for eight hours. Each morning, participants completed a computer task to measure how quickly they could access a list of numbers they had been asked to memorize. The list could be one, three, or five items long. Then participants were presented with a series of single digits and asked to answer "yes" or "no" to indicate whether each digit was one they had memorized. Those who slept eight hours a night steadily increased their working memory efficiency on this task, but those who slept only four hours a night failed to show any improvement in memory efficiency. Motor skill did not change across days for either group of participants.
http://www.eurekalert.org/pub_releases/2003-11/sfn-sfb_1111003.htm