Posts Tagged ‘REM’

Long Term Memory Consolidation and Sleep

September 12, 2019

This post is based on an important book by Scott D. Slotnick titled “Cognitive Neuroscience of Memory.” Remember to consult the website
to see the anatomical information referred to in this post.

It appears that a primary role of sleep is to integrate new memories into our vast memory store with the minimal disruption of old memories. Sleep involves rapid eye movements (REM) periods and non-REM periods that alternate every ninety minutes, with four stages of progressively deeper non-REM sleep. The first half of a night’s sleep is dominated by non-REM sleep, while the amount of REM sleep increases during the second half of the night. Non-REM stages 3 and 4, referred to as slow wave sleep, are of special relevance because these periods are important for consolidation of long-term memories. REM sleep seems to be particularly important for consolidation of implicit memories.

Slow wave sleep is associated with slow (less than 1 Hertz) waves of brain activity that are measured across the entire scalp using EEG. The slow waves orchestrate a number of brain processes that mediate the process of long-term memory consolidation. Slow waves alternate between down-states corresponding to global decreases in brain activity and upstates corresponding to global increases in brain activity. Slow waves synchronize other brain waves including thalamic-cortical sleep spindles (that oscillate at frequencies of 11-16 Hertz) and hippocampal sharp-wave ripples (that oscillate at a frequency of approximately 200 Hertz). Hippocampal sharp-wave ripples are of particular importance as they are known to coordinate the hippocampal-cortical interactions that reflect the reproduction of memories from the previous waking period. In brief, important long term memories from the previous waking period are replayed during slow wave sleep, which in turn strengthens these memories and results in consolidation. Although this mechanism for memory consolidation is based on strengthening of memory representations through repeated activations, it has been proposed that sleep may also weaken memory representation of unimportant events to provide a clean slate for next day’s events. It is interesting to note that Dr. Slotnick dedicates this book to his incredible daughter Sonya, for dominating my hippocampal sharp-wave spindles these past twelve years. This section should convince all readers that all-nighters are not only fruitless, but also counterproductive. One wants to have memories well-consolidated prior to taking an exam.

We Dream Much More Than we Know

April 21, 2017

This is the conclusion from a News Piece written  by Chelsea Whyte in the 15 April 2017 issue of the New Scientist.  A new way to detect dreaming has confirmed that it doesn’t only occur during rapid eye movement (REM) sleep, and has shown why we don’t often remember our dreams.

Tore Nielsen at the University of Montreal says, “There is  much more dreaming going on than we remember.  It’s hour and hours of mental experience, and we remember a few minutes.  Low-frequency  brainwaves are detectable across the brain.  Francesca Siclari and her colleagues at the University of Wisconsin-Madison have discovered that a decrease in these waves in an area at the back of the brain is a sign that  someone is dreaming.  She says, “This zone was a little bit more awake, showing high frequency  brainwaves more common during wakefulness.  This one region seems to be all that’s necessary for dreaming.”

Siclari and her team used EEG caps to map the brain activity of 32 people while they slept.  They woke the sleeper when they showed various patterns of brainwave activity, and asked them if they had been dreaming.  Some participants reported having dreams with a narrative structure, while others were more impressionistic.  One had a dream about reporting a dream

There was such a strong correlation between dreaming and fewer low-frequency  waves in the “Hot zone” that they could successfully predict whether a person was dreaming 91% of the time.

The team found that dreams during REM sleep were linked to a rise in high-frequency brainwaves in areas the are active in waking hours.  The activity matched the brain areas that would have been active if the dreamers had been living our their dreams in real life.  The team found that the participants dreamed during 71% of their non-REM sleep in addition to 95% of their REM sleep.

Many dreams are forgotten.  Sometimes participants had a foggy idea that they had been dreaming, but couldn’t remember  what about.  In a further experiment the team found that being able to later remember a dream was linked to higher activity in the prefrontal cortex, which is associated with memory, while dreaming.  Siclari says, “The region for remembering the dream was different from the region having a dream.

So dreaming is very important for our brains.  The previous posts on willpower have shown the importance of having adequate sleep for effective mental functioning.  It seems like both education and employment typically employ schedules that hinder sufficient sleep.  This issue needs serious public attention.

Journal reference:  Nature Neuroscience, DOI:  10.1038/nn.4545

© Douglas Griffith and, 2017. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Douglas Griffith and with appropriate and specific direction to the original content.


May 29, 2016

The Cover Page of the 28 May 2016 New Scientist has SLEEP THE GOOD SLEEP as the title.  According to Matt Walker of he University of California, Berkeley, “sleep has been labelled he this pillar of good health, along with diet, exercise.  But that’s underselling it:  sleep is the foundation on which these other two pillars rest.  There is no tissue within the body and no process within the brain that is not enhanced by sleep, or demonstrably impaired when you don’t get enough.”

Besides the well recognized benefits for memory consolidation, repair and growth sleep—or the lack of it— is now though to have a host of other ill effects.  Too little sleep messes with our emotions and our ability to make sound decisions.  It affects our immune systems and appetites, and has been linked to metabolic diseases such as obesity and type 2 diabetes.  Increasingly, a lack of sleep is implicated in mental health problems to include depression, bipolar disorder, schizophrenia, and neurological conditions such as Alzheimer’s disease.  One of the articles even makes the claim that too much sleep can be harmful, but other articles raise issues that seem to contradict this claim.  One of the reasons for this might be due to genetics and individual differences.

To account for these differences, the best rule of thumb is that we should not need an alarm clock to wake up in the morning.  In other words, we should wake up naturally.

Shift work has bad effects on health.  Unfortunately,  the jobs of many people require shift work.  Quantitative estimates of the damage caused by shift work would be useful for these people in determining whether they should seek different types of employment.  Catching up during weekends for lost sleep, although necessary, does not appear to make up for adverse healthy effects.  The thinking is that the dangers here might be comparable to those incurred via shift work.

Here are the phases of sleep.


REM — 25% of sleep at night.  First occurs about 90 minutes after falling asleep, then every 90 minutes.  These phases get longer later in the night.

STAGE 1 — light sleep.  Happens when we first doze off and just before waking.  Typically lasts for up to 7 minutes.  During this phase we’re prone to twitches, or hypnagogic  jerks.

STAGE 2 — deeper sleep.  Lasts up to about 25 minutes.  Brainwaves become slower and researchers can pick up “sleep spindles,” distinct patterns of brainwaves associated with memory consolidation.

STAGE 3 + 4 — final and deepest stages of non-REM sleep.  heart rate slows.  Lasts up to about 40 minutes.  Brain activity switches to “slow waves.”  Less aware of external noises.  If you’re aroused  from this stage of sleep, it can take up to an hour to become fully alert.

One might conclude from these stages of sleep that napping will not be beneficial.  This is not so.  According to a piece by Catherine de Lange a “nano-nap” lasting just 10 minutes can boost alertness, concentration, and attention for as much as 4 hours.  A “nano-nap”  takes 20 minutes and you increase your powers of memory and recall, too.  We are unlikely  to enter deeper stages of sleep, so we’ll avoid the phenomenon known as sleep inertia, which is the groggy feeling that can occur when waking from deep sleep.

Deep sleep does provide the biggest boost to learning.  Opt for a nap between 60 and 90 minutes, says Walker.  His research shows this aids learning by shifting memories from short-term storage in the brain’s hippocampi to lockdown in the prefrontal cortex, like clearing space on a USB memory stick.   In addition to aiding the retention of factual information, longer naps can increase motor memory, which is useful for training skills such as sport or playing a musical instrument.

A longer nap can also improve equanimity.  When we’re feeling emotional, we should try snoozing for 45 minutes or more.  This should take us through a stage of REM sleep, and brain scans of people following a REM sleep nap showed more positive responses to images and to pleasant experiences.

This post will conclude with statistics that can come in handy when conversations lull.

29 % of people in the US take their cellphones into the bedroom and use it when trying to get sleep (this is not a good idea).

34 minutes is the average extra sleep people get per night after drinking sour cherry juice before bed for 7 days.

67% of the time when men dream about people it’s about other men.  Women dream equally about men and women.

1.2  minutes of sleep is lost per night for each cigarette smoked during the day.

5 is the number of minutes it takes us to fall asleep if were sleep deprived.  The ideal is 10-15 minutes.

100 times an hour:  how often someone with sleep apnea might stop breathing in the night.

Sleep and a Healthy Memory

December 12, 2012

The Health & Science Section of the Washington Post included a piece of sleep1. Sleep is so important to a healthy memory that I feel compelled to relay the contents of that article to you. Our brains are active throughout the four stages of sleep, which are:

Stage 1: Falling asleep, which is characterized by Beta waves.

Stage 2: Light sleep, which is characterized by Alpha waves.

Stage 3: Deepest sleep, which is characterized by Theta waves.

Stage 4: Rapid Eye Movement (REM), which is characterized by Delta waves.

Memory and learning is impaired. The hippocampus is critical in transferring information into long term storage. Losing two hours of sleep in a single night can impair this information transfer. REM sleep is especially important because that appears to be when the brain filters out irrelevant information.

Missing a few hours sleep can result in accidents. This can produce “local sleep,” in which parts of the brain nod off while a person is nominally awake. One study found that middle school and high school athletes who slept eight or more hours each night were 60% less likely to be injured playing sports than those who slept less.

People who sleep four hours or less a night spend a lower percentage of time in Stage 2 and REM sleep. Consequently, they feel hungrier, crave more sweet and salty foods, and consume more calories than those who sleep longer. This makes them more susceptible to obesity and diabetes.

A study involving mice found that when Alzheimer’s plaques began to build in their brains, their sleep was disrupted. This suggests that poor sleep might be one of the first signs of the disease. It has also been found that connections between areas of a network in the brain used in daydreaming and introspection are disrupted in people who are chronically sleepy during the day. Alzheimer’s damages the same network, so these shaky connections might signal a susceptibility to the disease.

So, get a good night’s sleep. It is refreshing and will keep your memory healthy.

1Berkowitz B., & Cuadra, A. (2012). The Rest of the Story on Sleep. Washington Post, Health & Science, e2, December 4.

Why Do We Dream?

October 2, 2011

Given that we are asleep about one-third of our lives, and given that dreaming is a predominant part of sleeping, dreaming must be important. Researchers have been working on this problem for many years and an article1 in the New Scientist summarizes some recent research. Changes in electrical activity in the brain and movements of the eyes allow us to identify five stages of sleep. Sleep begins with two stages of light sleep, followed by two stages of deep sleep, followed by a stage of Rapid Eye Movement (REM) sleep. This sleep cycle lasts approximately 90 minutes and is repeated until we awaken.

One of the roles of dreaming is memory consolidation (See the Healthymemory Blog Post, “To Remember It, Sleep on It). There are a substantial number of studies reporting that sleep facilitates memory. The New Scientist article reported a study in which non-REM dreams boost people’s performance on a problem. The research participants were given an hour of training on a complex maze. Some participants were allowed to take a ninety-minute nap, while other participants were kept awake. When tested again on the maze, people who dreamed showed bigger improvements than people who did not dream. The largest improvements were in people who dreamed about the maze. This dream content could be somewhat bizarre. One of the participants who showed the largest improvement reported the following dream: “there were people at checkpoints in the maze as well as bat caves that he had visited a few years earlier.”

REM dreams contain more emotion, more aggression, and more unknown characters than non-REM dreams, whereas non-REM dreams are more likely to involve friendly encounters. A conjecture is that non-REM dreams help us practice friendly encounters, whereas REM dreams help us to rehearse threats. REM sleep strengthens negative emotional memories2 . The notion here is that if we don’t remember bad experiences, we will not learn from them. It is also thought that reliving the upsetting experience in the absence of the hormonal rush that accompanied the actual event helps to strip away the raw emotion from the memory. This is somewhat analogous to desensitization techniques employed by therapists. Although these REM dreams can be helpful for many situations, they do not work for people with Post Traumatic Stress Disorders. This is unfortunate.

So sleep and dreaming are activities that are important to both cognitive and emotional health. Shortchanging yourself of this needed activity has adverse effects on your memory health.

1Young, E. (2011). The I in Dreaming. New Scientist, 12 March, 36-39.

2Cerebral Cortex, vol 19, p.1158