sleep memory

Memories are strengthened via brainwaves produced during sleep

Researchers use medical imaging to map areas involved in recalling learned information while we slumber

May 15, 2019

Science Daily/Concordia University

Researchers have known about the close relationship between sleep and memory for decades. Now, a new study published in the journal NeuroImage looks at one important mechanism in that relationship. The research brings us closer to understanding how learned information turns into reliable memories during sleep.


The study was led by Thanh Dang-Vu, associate professor in the Department of Health, Kinesiology and Applied Physiology and Concordia University Research Chair in Sleep, Neuroimaging and Cognitive Health. In it, researchers studied how declarative information like facts and faces get stored after they have been learned. It has to do with brainwaves -- specifically, ones called sleep spindles, which are fast bursts of electrical activity produced by neurons mainly during Stage 2 sleep, prior to deep sleep.


Dang-Vu worked alongside Christophe Grova, associate professor in the Department of Physics, and researchers from the Cyclotron Research Centre at University of Liège in Belgium. Using medical imaging machines, they were able to assess brain activity related to these waves.


"It's hypothesized that sleep spindles play an important role in transferring information from the hippocampus to the neo-cortex," Dang-Vu says. "This has the effect of increasing the strength of memories."


To get the images they needed, Dang-Vu's team used both electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). They applied these tools to a group of student volunteers during and after a lab-based face-sequencing task. The students were shown a series of faces and asked to identify the order in which they were shown. The researchers scanned them while they were learning the faces, while they were asleep and again when they woke up and had to recall the sequences.


Sleep spindles reactivated

 They then came back every day for a week and repeated the task without being scanned. After a week had elapsed, they had memorized the task, and were once again scanned during sleep and asked to recall the sequences.


"Our aim was to compare the sleep spindles from the night where the subjects learned the new information to the night where they didn't have any new information to learn but were exposed to the same stimulus with the same faces," Dang-Vu explains.


The researchers found that during spindles of the learning night, the regions of the brain that were instrumental in processing faces were reactivated. They also observed that the regions in the brain involved in memory -- especially the hippocampus -- were more active during spindles in the subjects who remembered the task better after sleep.


This reactivation during sleep spindles of the regions involved in learning and memory "falls in line with the theory that during sleep, you are strengthening memories by transferring information from the hippocampus to the regions of the cortex that are important for the consolidation of that specific type of information," he says.


Using non-invasive imaging to identify the mechanisms that strengthen memories can, he hopes, lead to improvements in our understanding of how memories work -- and can lead to improved interventions for people with sleep or memory issues.

Cueing newly learned information in sleep improves memory, and here's how

March 8, 2018

Science Daily/Cell Press

Scientists have long known that sleep is important to the formation and retention of new memories. Memory consolidation is associated with sudden bursts of oscillatory brain activity, called sleep spindles, which can be visualized and measured on an electroencephalogram (EEG). Now researchers have found that sleep spindles also play a role in strengthening new memories when newly learned information is played back to a person during sleep.


The findings provide new insight into the process of memory consolidation during sleep. They may also suggest new ways to help people remember things better, according to the researchers.


"While it has been shown previously that targeted memory reactivation can boost memory consolidation during sleep, we now show that sleep spindles might represent the key underlying mechanism," says Bernhard Staresina of the University of Birmingham in the United Kingdom. "Thus, direct induction of sleep spindles -- for example, via transcranial electrical stimulation -- perhaps combined with targeted memory reactivation, may enable us to further improve memory performance while we sleep."


Sleep spindles are half-second to two-second bursts of brain activity, measured in the 10-16 Hertz range on an EEG. They occur during non-rapid eye movement sleep stages two and three. Earlier studies had shown that the number of spindles during the night could predict a person's memory the next day. Studies in animals also linked sleep spindles to the process by which the brain makes new connections. But many questions about the link between sleep spindles and reactivated memories during sleep remained.


Staresina along with Scott Cairney at the University of York, UK, suspected that experimental reactivation of memories might lead to a surge of sleep spindles in a sleeping person's brain. To find out, they devised an experiment in which people learned to associate particular adjectives with particular objects and scenes. Some study participants then took a 90-minute nap after their study session, whereas others stayed awake. While people napped, the researchers cued those associative memories and unfamiliar adjectives.


As expected, the researchers saw that memory cues led to an increase in sleep spindles. Interestingly, the EEG patterns during spindles enabled the researchers to discern what types of memories -- objects or scenes -- were being processed.


The findings add to evidence for an important information-processing role of sleep spindles in the service of memory consolidation, the researchers say.


"Our data suggest that spindles facilitate processing of relevant memory features during sleep and that this process boosts memory consolidation," Staresina says.


This new understanding of the way the brain normally processes and strengthens memories during sleep may help to explain how that process may go wrong in people with learning difficulties, according to the researchers. It might also lead to the development of effective interventions designed to boost memory for important information.

New insights into why sleep is good for our memory

November 14, 2017

Science Daily/University of York

Researchers have shed new light on sleep's vital role in helping us make the most of our memory.


Sleep, they show, helps us to use our memory in the most flexible and adaptable manner possible by strengthening new and old versions of the same memory to similar extents.


The researchers also demonstrate that when a memory is retrieved -- when we remember something -- it is updated with new information present at the time of remembering. The brain appears not to 'overwrite' the old version of the memory, but instead generates and stores multiple (new and old) versions of the same experience.


The results of the research, carried out at York's Sleep, Language and Memory (SLAM) Laboratory, are presented in the journal Cortex today.


Lead researcher Dr Scott Cairney of York's Department of Psychology said: "Previous studies have shown sleep's importance for memory. Our research takes this a step further by demonstrating that sleep strengthens both old and new versions of an experience, helping us to use our memories adaptively.


"In this way, sleep is allowing us to use our memory in the most efficient way possible, enabling us to update our knowledge of the world and to adapt our memories for future experiences."


In the study, two groups of subjects learned the location of words on a computer screen. In a test phase, participants were presented with each of the words in the centre of the screen and had to indicate where they thought they belonged.


One group then slept for 90 minutes while a second group remained awake before each group repeated the test. In both groups, the location recalled at the second test was closer to that recalled at the first test than to the originally-learned location, indicating that memory updating had taken place and new memory traces had been formed.


However, when comparing the sleep and wake groups directly, the locations recalled by the sleep group were closer in distance to both the updated location (i.e. previously retrieved) and the original location, suggesting that sleep had strengthened both the new and old version of the memory.


Corresponding author Professor Gareth Gaskell of York's Department of Psychology said: "Our study reveals that sleep has a protective effect on memory and facilitates the adaptive updating of memories.


"For the sleep group, we found that sleep strengthened both their memory of the original location as well as the new location. In this way, we were able to demonstrate that sleep benefits all the multiple representations of the same experience in our brain."


The researchers point out that although this process helps us by allowing our memories to adapt to changes in the world around us, it can also hinder us by incorporating incorrect information into our memory stores. Over time, our memory will draw on both accurate and inaccurate versions of the same experience, causing distortions in how we remember previous events.


The study builds on a research model created by Ken Paller, Professor of Psychology at Northwestern University, USA, an eminent researcher in the field of memory and a co-author on this study.

Memory Links to 40 Winks

July 6, 2010

Science Daily/Washington University in St. Louis

When it comes to executing items on tomorrow's to-do list, it's best to think it over, then "sleep on it," say psychologists at Washington University in St. Louis.


People who sleep after processing and storing a memory carry out their intentions much better than people who try to execute their plan before getting to sleep. The researchers have shown that sleep enhances our ability to remember to do something in the future, a skill known as prospective memory.


Moreover, researchers studying the relationship between memory and sleep say that our ability to carry out our intentions is not so much a function of how firmly that intention has been embedded in our memories. Rather, the trigger that helps carry out our intentions is usually a place, situation or circumstance -- some context encountered the next day -- that sparks the recall of an intended action.


The researchers found that participants who tested in the morning following sleep overwhelmingly performed the prospective memory task better in the semantic category test, or context, than in the other two, and they found no such correlation in the group who tested sleepless.


The crux of the finding rests on the fact that the prospective memory instruction was given right after the semantic category practice. In this context, those who slept remembered the prospective memory intention better than in the other categories.


"Sleep promoted the remembering to do the prospective memory task when that one context was present, but not when some other context was present," McDaniel says. "That's because of temporal contiguity -- the fact that the participants were told to hit that 'Q' button right after they were exposed to the semantic category context.


"The idea is that the semantic category test is weakly associated with the prospective memory intention -- it's weakly floating around in the mind and becomes weakly associated with the prospective memory test," McDaniel says.


To return to the colleague and message analogy, because before sleeping you remembered you had a message to deliver to your colleague and you would see him in the conference room tomorrow, sleep enhances the likelihood that you will tell him in the conference room, but not in some other context, the office, elevator, the mail room, for example.


The researchers believe that the prospective memory process occurs during slow wave sleep -- an early pattern in the sleep cycle -- involving communication between the hippocampus and cortical regions. The hippocampus is very important in memory formation and reactivation and the cortical regions are keys to storing memories.


"We think that during slow wave sleep the hippocampus is reactivating these recently learned memories, taking them up and placing them in long-term storage regions in the brain," Scullin says. "The physiology of slow wave sleep seems very conducive to this kind of memory strengthening."

Direct Evidence of Role of Sleep in Memory Formation is Uncovered

September 16, 2009

Science Daily/Rutgers University

A research team has pinpointed for the first time the mechanism that takes place during sleep that causes learning and memory formation to occur. The team has determined that short transient brain events, called “sharp wave ripples,” are responsible for consolidating memory and transferring the learned information from the hippocampus to the neocortex, where long-term memories are stored.


A Rutgers University, Newark and Collége de France, Paris research team has pinpointed for the first time the mechanism that takes place during sleep that causes learning and memory formation to occur.


It’s been known for more than a century that sleep somehow is important for learning and memory. Sigmund Freud further suspected that what we learned during the day was “rehearsed” by the brain during dreaming, allowing memories to form. And while much recent research has focused on the correlative links between the hippocampus and memory consolidation, what had not been identified was the specific processes that cause long-term memories to form.


“This is the first example that if a well-defined pattern of activity in the brain is reliably and selectively eliminated, it results in memory deficit; a demonstration that this specific brain pattern is the cause behind long-term memory formation,” says Buzsaki.


The research also represents a move toward a new direction in neuroscience research. While previous research largely has focused on correlating behavior with specific brain events through electroencephalogram, neuronal spiking and functional magnetic resonance imaging studies, increasingly researchers are challenging those correlations as they seek to identify the specific process or processes that cause certain events and behaviors to take place.

Sleep Helps Reduce Errors in Memory

September 11, 2009

Science Daily/Michigan State University

Sleep may reduce mistakes in memory, according to a first-of-its-kind study led by a cognitive neuroscientist at Michigan State University.


The findings, which appear in the September issue of the journal Learning & Memory, have practical implications for everyone from students flubbing multiple choice tests to senior citizens confusing their medications, said Kimberly Fenn, principal investigator and MSU assistant professor of psychology.


“We know older individuals generally have worse memory performance than younger individuals. We also know from other research that elderly individuals tend to be more prone to false memories,” Fenn said. “Given the work we’ve done it’s possible that sleep may actually help them to reject this false information. And potentially this could help to improve their quality of life in some way.”

Sleep And Memory

January 3, 2017

By Anne Foy, Guest Contributor

For some years now, the world appears to have seen sleep as an inconvenience. Sure, we acknowledge that it’s something which needs to happen. We’re even aware of the dire consequences [1] of not getting enough sleep [2]. But we nonetheless try to push it to the margins of our existence. We force ourselves out of bed before we’re fully awake, and, at the other end of the day, bludgeon our exhausted brains into keeping us awake for longer. We stifle sleep with caffeine, or bring it on artificially with pills [3]. We try to make it into our servant, to be called upon at times of our choosing and hidden away when not wanted. Little wonder that so many of us are struggling with sleep disorders. However, poor sleep does a lot more than simply make us feel groggy and slow. Over time, chronic lack of sleep can have a very serious impact upon your cognition. In particular, sleep is associated with good memory function - so much so that disordered sleeping habits are associated with dementia.

More Than Just ‘Recharging’ Time

There is a common misconception that sleep is about ‘switching off’ in order to ‘recharge’. Humans aren’t cellphones, however. We’re far, far more complicated than that. Sleep is in fact the time when your body and mind carries out some of its most complex operations - the kind of thing it doesn’t want your conscious mind and day to day life interrupting. This is why doctors and healthcare providers [4] are eager for patients to sleep well - without good sleep, a lot of these vital health and maintenance operations go undone, leading to myriad health issues down the line. One of these vital operations is the sorting and processing of memories. We’ve known for a long time that sleep plays an incredibly important role in healthy memory, but haven’t been entirely sure precisely what it does or how it does it. Recently, however, a lot of facts about sleep and memory have been discovered [5] - and revealed serious implications about lack of sleep and cognitive decline.

Deep Sleep Neuron Connections

When we’re in deep, ‘slow-wave’ sleep, our brains effectively ‘replay’ what we’ve experienced during the day. As we’re asleep, it’s able to do this without cognitive interruption, and therefore ‘concentrate’ (for want of a better word) on what it’s experienced. During deep sleep, scientists have observed [6] brains making lots of new connections between neurons. New connections forming between neurons is what ‘learning’ looks like from a neurobiological perspective. From a psychological perspective, ‘learning’ involves taking memories, extrapolating from them, and then storing those memories in ‘long-term’. This is the process the scientists observed occurring in the brains of sleeping subjects.

Lack Of Sleep And Dementia

Quite obviously, if your brain uses its deep sleep time to sort through, store, and learn from memories, a lack of deep sleep is going to cause issues with memory. However, it seems to go a lot deeper than the odd spate of simple forgetfulness. Studies show that disturbed sleep patterns can significantly increase one’s chances of developing dementia. As yet, nobody is entirely sure why this should be the case, but the facts are indisputable [7], and many are reasonably sure that it has something to do with sleep’s role in memory formation. Some speculate that lack of usage during deep sleep causes the brain's memory-retention functions to degrade. Others believe that lack of sleep generally puts an inordinate amount of strain on the brain, causing cell death and therefore cognitive decline.All in all, whatever is actually going on inside the skull, if you want to learn more, remember more, and generally maintain good cognitive health, it’s best to sort out your sleep cycle - and quickly!

[1] Think!, “Fatigue”, UK Government

[2] Mercola, “How Dangerous Is Sleep Deprivation, Really?”, Mar 2014

[3] Ny Daily News, “CDC: 9 million Americans use prescription sleeping pills”, Aug 2013

[4] Q, "health cover"

[5] James Gallagher, “Sleep’s memory role discovered”, BBC, Jun 2014

[6] Guang Yang, Cora Sau Wan Lai, Joseph Cichon, Lei Ma, Wei Li, Wen-Biao Gan, “Sleep promotes branch-specific formation of dendritic spines after learning”, Science, Jun 2014

[7] Caroline Cassels, “Disturbed Sleep Linked To Increased Dementia Risk”, Medscape, Jul 2014


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