Consolidation: Research reports

consolidation

August 2005

Protein found to inhibit conversion to long-term memory

In a study using genetically engineered mice, researchers have found that mice without a protein called GCN2 acquire new information that doesn’t fade as easily as it does in normal mice. After weak training on the Morris water maze, their spatial memory was enhanced, but it was impaired after more intense training. The researchers concluded that GCN2 may prevent new information from being stored in long-term memory, suggesting the conversion of new information into long-term memory requires both the activation of molecules that facilitate memory storage, and the silencing of proteins such as GCN2 that inhibit memory storage.
The study was published in the August 25 issue of Nature. Full reference
http://www.eurekalert.org/pub_releases/2005-08/uom-mrp082905.htm

January 2005

New theory challenges current view of how brain stores long-term memory

The current view of long-term memory storage is that, at the molecular level, new proteins are manufactured (a process known as translation), and these newly synthesized proteins subsequently stabilize the changes underlying the memory. Thus, every new memory results in a permanent representation in the brain. A new theory of memory storage suggests instead that there is no permanent representation. Rather, memories are copied across many different brain networks. The advantage is that it is a highly flexible system, enabling rapid retrieval even of infrequent elements.
The theory suggests that the brain stores long-term memory by rapidly changing the shape of proteins already present at those synapses activated by learning. The theory explains a number of phenomena that are not properly answered by the existing theory. The theory doesn’t disagree with the view that it is the synapse that is modified in response to learning; the disagreement concerns how that synaptic modification occurs. Current theory says it is brought about by recently synthesized proteins; the new theory suggests that learning leads to a post-synthesis (post-translational) synaptic protein modification that results in changes to the shape, activity and/or location of existing synaptic proteins. It is suggested that long-term memory storage relies on a positive-feedback rehearsal system that continually updates or fine-tunes post-translational modification of previously modified synaptic proteins, thus allowing for the continual modifications of memories.
The theory was outlined the in the January issue of Trends in Neuroscience. Full reference
http://www.eurekalert.org/pub_releases/2005-01/nu-ntc011405.htm
http://www.sciencedirect.com/science/journal/01662236

October 2004

Brain circuit crucial for memory consolidation identified

A rat study has identified a circuit in the brain that appears crucial in converting short-term memories into long-term memories. The circuit is the temporoammonic (TA) projection, which directly links the CA1 region of the hippocampus and the neocortex.
The findings were published in the October 7 issue of Nature. Full reference
http://www.eurekalert.org/pub_releases/2004-10/hhmi-bcm100604.htm

May 2004

Confirmation that a memory code is held in many different regions

Mapping of brain activity patterns has cast new light on how our memories integrate sights, smells, tastes, and sounds. Previous research has shown that the visual and auditory brain regions are activated during memories of pictures and sounds. A new imaging study investigated taste and smell. Volunteers were presented with random combinations of an odor and the image of an object and asked to imagine a link or story that associated the two. They were then presented with a series of both previously seen images and new images and asked to recall whether they were viewing new or old images. It was found that the region involved in processing smells, the piriform cortex, was activated when participants saw objects previously associated with odors. On questioning, participants said they recalled the story linking image and smell, but had not tried to summon up the smell itself. These findings confirm models of memory recall in which the sensory-specific components of a memory are preserved in the sensory-related brain regions, and the hippocampus draws on those components to reconstruct a sensory-rich memory (as opposed to the complete memory being stored in one place). This allows memories to be recalled from one sensory cue.
The research was reported in the May 27 issue of Neuron. Full reference
http://www.eurekalert.org/pub_releases/2004-05/cp-hoh052104.htm
http://www.eurekalert.org/pub_releases/2004-05/ucl-ros052404.htm

June 2003

Another step in understanding how memories are formed

The electrical activity of individual neurons in the brains of two adult rhesus monkeys was monitored while the monkeys played a memory-based video game in which an image pops up on the computer screen with four targets—white dots—superimposed on it. The monkeys’ task was to learn which target on which image was associated with a reward (a drop of their favorite fruit juice). Dramatic changes in the activity of some hippocampal neurons, which the scientists called "changing cells", paralleled their learning, indicating that these neurons are involved in the initial formation of new associative memories. In some of the cells, activity continued after the animal had learned the association, suggesting that these cells may participate in the eventual storage of the associations in long-term memory.
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://www.sciencentral.com/articles/view.htm3?language=english&type=article&article_id=218391998

January 2003

More details about how memories are formed in the hippocampus

We know how important the hippocampus is in forming memories, but now, using newly developed imaging techniques, researchers have managed to observe how activity patterns within specific substructures of the hippocampus change during learning. The study identified areas within the hippocampus (the cornu ammonis and the dentate gyrus) as highly active during encoding of face-name pairs. This activity decreased as the associations were learned. A different area of the hippocampus (the subiculum) was active primarily during the retrieval of the face-name associations. Activity in the subiculum also decreased as retrieval became more practiced.
The report appeared in the January 24 edition of Science. Full reference
http://www.eurekalert.org/pub_releases/2003-01/uoc--som012303.htm

May 2002

Memories may be hard to find when thalamus fails to synchronize rhythms

Memory codes - the representation of an object or experience in memory - are patterns of connected neurons. The neurons that are linked are not necessarily in the same region of the brain. Exciting new research has measured the electrical rhythms that parts of the brain use to communicate with each other and found that the thalamus regulates these rhythms. "Memory appears to be a constructive process in combining the features of the items to be remembered rather than simply remembering each object as a whole form. The thalamus seems to direct or modulate the brain's activity so that the regions needed for memory are connected." The authors suggest that tips of the tongue experiences (when only part of a memory is recalled) may occur when the rhythms don't synchronize with the regions properly.
The study was published in the April 30 issue of Proceedings of the National Academy of Science (USA). Full reference
http://www.eurekalert.org/pub_releases/2002-05/uoaf-mi050902.htm

November 2001

Pictures show how nerve cells form connections to store memories

Scientists at the University of California, San Diego have produced dramatic images of brain cells forming temporary and permanent connections in response to various stimuli, illustrating for the first time the structural changes between neurons in the brain that, many scientists have long believed, take place when we store short-term and long-term memories.
The report appears in the 30 November issue of Cell. Full reference
http://ucsdnews.ucsd.edu/newsrel/science/mccell.htm

The neural bases of effective encoding

Failure to remember experiences often occurs not because the memory is hard to retrieve, but because it was not properly encoded in the first place. Imaging studies are beginning to give us a better idea of the neurocognitive processes that lead to more effective encoding.
The report appears in the November issue of Current Biology. Full reference
http://tinyurl.com/i87x

Imaging study confirms role of medial temporal lobe in memory consolidation

Lesions in the medial temporal lobe (MTL) typically produce amnesia characterized by the disproportionate loss of recently acquired memories. Such memory loss has been interpreted as evidence for a memory consolidation process guided by the MTL. A recent imaging study confirms this view by showing temporally graded changes in MTL activity in healthy older adults taking a famous faces remote memory test. Evidence for such temporally graded change in the hippocampal formation was mixed, suggesting it may participate only in consolidation processes lasting a few years. The entorhinal cortex (also part of the MTL) was associated with temporally graded changes extending up to 20 years, suggesting that it is the entorhinal cortex, rather than the hippocampal formation, that participates in memory consolidation over decades. The entorhinal cortex is damaged in the early stages of Alzheimer’s disease (AD).
The report appeared in Nature neuroscience. Full reference
http://www.nature.com/neurolink/v4/n11/abs/nn739.html

September 2001

Crucial enzyme for consolidating long-term memories

Susumu Tonegawa and colleagues at the Massachusetts Institute of Technology and the Vollum Institute have released the first of a series of studies illuminating how short-term memories are turned into long-term ones via consolidation, how different types of learning occurs in unexpected ways, and how memory recall occurs. In this first study, the researchers eliminated the function of a single enzyme in a restricted memory-related region in the brains of mice, and thus showed that the enzyme is important in consolidating long-term memories. While this enzyme (calcium-calmodulin dependent kinase (CaMKIV)), has been implicated in the process of establishing long-term memories, previous research has been inconclusive because the techniques used to knock out the enzyme were so global. A series of behavioral experiments led the researchers to conclude that the CaMKIV pathway was primarily involved in memory consolidation and retention. However, memory consolidation was not completely extinguished, suggesting that there may be parallel signaling pathways involved in consolidation, or that there may have been incomplete knockout of CaMKIV activity.
The report was published in the September 21 issue of Cell. Full reference
http://www.hhmi.org/news/tonegawa.html
http://www.eurekalert.org/pub_releases/2001-09/hhmi-rfe092001.htm

May 2001

Protein that allows information to be converted from short-term into lifelong memories identified

Scientists from UCLA and Johns Hopkins University have taken the first step in discovering how the brain, at the molecular and cellular level, converts short-term memories into permanent ones."Memories last different amounts of time," Frankland said. "You might remember a phone number for just a few minutes, for example, while certain childhood events will be remembered for a lifetime. Our study reveals the role of a protein that must be present in the cortex for information to be converted from short-term into lifelong memories."
The study is reported in the May 17 issue of Nature. Full reference
http://www.eurekalert.org/pub_releases/2001-05/UNKN-BrfU-1505101.htm

December 2000

Specific molecule that helps brain reorganize in the face of new experiences targeted

For the first time scientists have been able to pinpoint a specific molecule that assists the brain to reorganize in the face of new experiences. Neuroscientists at the University of Rochester Medical Center found that genetically engineered mice that were challenged with new tasks improved their learning abilities. The team then boosted the amount of the molecule, nerve growth factor (NGF), in their brains, and found that the mice learned to run unfamiliar mazes more quickly than their unmodified counterparts.
The study was published in the Proceedings of the National Academy of Science.
http://www.eurekalert.org/pub_releases/2000-12/UoR-Simt-2612100.htm

Reconsolidation

February 2006

Reactivating single memory does not affect associated memories

Recent studies have indicated that consolidated memories can in fact be manipulated when reactivated. This process, often referred to as reconsolidation, has been proposed as a possible way of treating traumatic memories. But one concern is that reactivating and disrupting a single memory may also affect other associated memories. A new rat study has found that only those memories directly reactivated are vulnerable, not those associated to them.
The study appeared in the February 28 issue of the Proceedings of the National Academy of Sciences. Full reference
http://www.eurekalert.org/pub_releases/2006-02/nyu-nrs021306.htm

March 2004

Memories are harder to forget than recently thought

Previous rodent studies have shown that the process of encoding a memory can be blocked by the use of a protein synthesis inhibitor called anisomycin ( http://www.eurekalert.org/pub_releases/2000-08/NYU-Nnfl-1508100.htm). Experiments with anisomycin helped lead to the acceptance of a theory in which a learned behavior is consolidated into a stored form and that then enters a 'labile' - or adaptable - state when it is recalled. According to these previous studies, the act of putting a labile memory back into storage involves a reconsolidation process identical to the one used to store the memory initially. Indeed, experiments showed that anisomycin could make a mouse forget a memory if it were given anisomycin directly after remembering an event. In a new study, however, researchers have showed that disruption of a "re-remembered" memory was not permanent. Mice demonstrated that they could remember the original learned behavior 21 days later. This research thus casts doubt on the concept of “reconsolidation”, or at least demonstrates that we still have much to learn about this process.
The study was published in the March 30 issue of Proceedings of the National Academy of Science. Full reference
http://www.eurekalert.org/pub_releases/2004-03/uop-mah031504.htm

How sleep helps consolidation

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.