Tag Archives: sleep

Why We Sleep

The question arises of what exactly is the purpose of sleep.  The short answer is that we don’t know exactly.  However, as the science of sleep progresses, our understanding as to the true purpose of sleep will likely be elucidated.

The fact that in deep NREM sleep physical and mental activity slow down considerably, has led to the reasonable speculation that this phase of sleep serves as a recovery and recharging function. While lower species don’t have REM sleep, almost all species do have NREM suggesting that this phase of sleep has a restorative function. When you’re in NREM you’re recharging your batteries. More specifically, N3 sleep or deep sleep is felt to be the most restorative.

This recharging function is essential because a prime consideration of both the brain and body is energy production and conservation. The brain’s prime goal is survival and its primary defense system, the fight/flight system, uses a lot of energy. Thus the production and conservation of energy is a critical function and it is assumed that NREM fills this role. When people are deprived of NREM sleep they do continue to feel very tired and the body tries to compensate for this on subsequent sleep occasions.

If NREM is about energy conservation, what is REM? Paradoxically REM uses a lot of energy. Perhaps the NREM phase of recovery, mentioned above, is among other things, designed to ensure that there’s enough energy for the REM phase?

Some researchers have argued that because of the high energy output in REM, the energy conservation of sleep overall is pretty small, particularly compared to being awake and just resting. Others have pointed out that if restoration of energy was the purpose of sleep, large animals should require more sleep, but in fact they sleep less.

One view of the energy consuming REM phase of sleep is that its main function is the consolidation of memories formed during the day. This would be crucial for learning and indeed young children do seem to require more REM than adults. One metaphor that might be useful here is that during the REM phase of sleep, the brain is filing away the day’s events. As you open the relevant filing cabinet you will see other associated ideas and other relevant recent events and their associations. If that were the case, our dreams would involve recent events and associations these events have with past experiences. Of course, a lot of dreams are like that. Moreover, the dreamer’s emotional state at the time of the dream would likely shape the dream sequence. So it’s likely that some consolidation of memories occurs during REM sleep and this process helps to explain dreaming.

While the consolidation of memories might be an efficient use of sleep time, it doesn’t appear too critical to functioning. As mentioned above, many species don’t even have a REM sleep phase, and when REM is suppressed it doesn’t appear to affect basic functioning.  However, in humans, when REM is suppressed for while, as in heavy alcohol consumption, there is a period after the REM suppression in withdrawal, during which there is increased amounts of REM sleep, what is called REM rebound.

The evidence is not overwhelming but it is reasonable to assume that NREM sleep serves some energy restoration function and that NREM sleep serves some neural consolidation of memories and learning.

Now we have a better understanding of sleep, it has allowed us to research sleep patterns and determine the type, rate and costs of poor quality sleep, reduced sleep time, or a combination of both. And we have been unable to expose the myth, common until about 20 years ago, that sleep deprivation or poor quality sleep doesn’t cause serious health and economic consequences.

History of Sleep


History of Sleep
While it seems obvious that humans have slept throughout their history, the way they did so in the past might be different from how we sleep today. For example, in his famous Oddysey written around 800 BC, Homer writes about people having two very distinct periods of sleep at different times of the 24 hour cycle. About three hundred years later, the Greek Alcmaeon observed that blood seemed to be draining from the vessels as we sleep, and assumed that this was a cause of it. Similarly, around 400B.C., Hippocrates noted that bodies cool during sleep and that sleep was therefore characterized by blood retreating from the periphery. Not long after that, Aristotle suggested that sleep was brought on by the warming of the body through digestion. Of course, such an observation would be heavily influenced by what one was eating and drinking and certainly rich foods and plentiful amounts of wine could have people nodding off in no time.

Up until about 162 A.D., the view was that the heart, not the brain, was the center of influence from which all bodily actions were controlled. It was Galen who suggested that the brain was the body’s control center and not the heart, leading to sleep theories that were centered on brain rather than heart activity. Subsequent research suggests that the ancients weren’t totally wrong about the heart. It turns out that there are about 50,000 neurons (brain cells) in the heart that connect with the brain. And there are 500 million neurons in the gut, so perhaps Aristotle’s connection between sleeping and eating wasn’t entirely off the mark.

Despite Descartes’ effort during the Renaissance to divide mind and body, much of the subsequent work focused on the brain’s control of the sleep process. In 1650, Dr. Willis identified the functions of different parts of the brain; in 1929, Hans Berger invented the EEG, which opened the study of the brain and its activity. Later, various areas of the brain were identified with the specific functions of sleep.

Specific identification and treatment for sleep disorders emerged in the twentieth century. In 1903 the first sleeping pill was introduced and in 1930 the first stimulant treatment for narcolepsy was developed. Restless Leg Syndrome (RLS) was first described by a Swedish doctor in 1945 and other conditions were subsequently diagnosed; for example, Dr. Schenk and colleagues first reported on a group of patients who didn’t demonstrate the usual muscle paralysis when in REM. In the last seventy years, there has been even more research, which has been able to identify the different stages and phases of sleep.

Nathaniel Kleitman was one of the pioneers of sleep research, with an interesting personal history. Arriving in New York as a penniless 20-year-old in 1915, he went on to get a PhD and conduct some of the earliest research on sleep and the brain. Using a crude EEG machine that used about half a mile of paper each time it ran a sleep test, Kleitman noticed the different stages of sleep, especially dreaming sleep. In a 1953 paper, he and his colleague, Eugene Aserinsky, called this stage of sleep “Rapid Eye Movement.” Kleitman, who lived to be 104, was fascinated by the concept of wake/sleep cycles and even conducted research on the effects of sleeping in caves and submarines.

One of Kleitman’s proteges, William Dement, continued the tradition of researching the brain and sleep using EEG technology. Dement was interested in sleep dysfunction and has contributed enormously to the diagnosis and treatment of sleep disorders. He is widely considered the father of sleep medicine. He launched what is now known as the American Academy of Sleep medicine and served as president for twelve years. Dement also played bass as a jazz musician and has even played with musical greats, Ray Charles and Quincy Jones.

Dement formed the Stanford University Sleep Disorders Clinic which has been the home to a great deal of important sleep research and some other very influential researchers. One of these is Christian Guillemenault, a prolific researcher, who has written more than 600 academic papers. His most noted work has been on the subject of sleep apnea. He co-opted cardiologists to measure and observe blood pressure and cardiac function in people who have what we now know as sleep apnea. In fact, Guillemenault was one of the first to use the term ‘obstructive sleep apnea’ and was the first to use tracheostomies to free the airways, both providing relief to sufferers as well as convincingly demonstrating the relationship between apnea and cardiovascular function.

Despite the work of these pioneers, sleep medicine research and literature lagged behind that of the other key lifestyle behaviors, like nutrition and exercise. It is only in the past decade has there been a recognition of the importance of sleep, elevating it to a science more in keeping with its importance.

What is Sleep?


What is sleep?

Regardless of the various theories, we know that sleeping is a natural function common to all humans and animals, too. We are designed to function on a wake/sleep cycle, although with the advent of artificial light (thank you, Edison for the 1879 introduction of the light bulb), energy boosting drinks, foods and medications, that cycle can be severely disrupted. However, it is clear that daily sleep is the preferred default setting for humans and that sleeping serves some very important functions that underpin health and wellbeing. However, there isn’t a complete agreement on what the functions of sleep actually are.

Sleep can simply be described as a state of reduced sensory and environmental responsiveness and physical inactivity. By comparison, wakefulness is characterized by, sensory perception, thinking, environmental responsiveness and physical activity.

There are various stages of sleep in mammals; the two most prominent are Rapid Eye Movement (REM) and non-REM (NREM) sleep. These two phases are quite different.

In REM sleep, muscles are effectively paralyzed, what is called atonia, and dreaming occurs. Obviously, it’s a good design feature to be paralyzed while dreaming otherwise many of us would be sleep walking and acting out or dreams with physical actions. This atonia is achieved through muscle inhibition by parts of the brain that regulate movement.    Interestingly, there is a sleep disorder called REM Behavior Disorder which is characterized by individuals acting out their dreams.

In REM there is also an increase in breathing and heart rate variability. In addition, in REM the brain also uses a lot of energy, which is important because one theory of sleep is that it is about energy conservation, which might seem paradoxical. There is obviously a lot of mental activity in REM unlike in the other sleep phase, which has earned the REM phase of sleep “paradoxical sleep.”  Core temperature is less well regulated in REM but sexual arousal is common and independent of dream content. In other words, physiology comes first and arousal is experienced, which may or may not be incorporated into a dream’s content.

NREM sleep is characterized as featuring general immobility, regular respiration and heart rate, and slow mental activity. It is divided into three parts:

N1: falling asleep, just in that border between nodding off but still easily awoken

N2: breathing and heart rate slow as you drift off to sleep

N3:  the slow wave delta phase that characterizes NREM. The hallmark feature of N3 sleep is slow, high amplitude delta waves on EEG.  The first episode lasts 45-90 minutes but gets progressively shorter though the night. Children tend to have more N3 sleep than older individuals.

These two phases of sleep are so different that they have led to speculation that there is more than one function of sleep and those functions are represented by these quite different states.

In addition to these separate and distinct sleep states, there is also a typical pattern of sleep in humans as we move in and out of these different phases.

Brain Wave Activity

Delta: 1-4 cycles per second: Deep sleep. Typical NREM phase

Theta: 5-8 cycles per second: Conscious, but low level of brain activation, e.g. meditation.

Alpha: 9-13 cycles per second: Relaxed wakefulness

Beta: 14-30 cycles per second: Active processing, stress.

Sleep Cycles

Sleep occurs in cycles that typically last 90 minutes; the ultradian sleep cycle.  Sleep proceeds from NREM phase to a REM phase, about five times a night. There is typically more NREM in the earlier part of sleep and more REM in the later part of the night or early morning. This is why people commonly awaken during their dreams.  REM accounts for between 20% and 25% of total sleep time.

The way in which a person cycles through these phases, as well as the quality of the stages of sleep, determines the healthiness or otherwise of sleep. There are almost 80 distinct types of sleep disorders, which reflect different dysfunctions in the stages and phases of sleep.

Sleep and Diet

Obtaining a good night’s sleep is vital to maintaining good health. Without adequate quality sleep, an individual will begin to suffer both mental and physical deficits. In this situation, many individuals complain to their doctors and receive with a prescription for hypnotics or other sleeping pills.

While this might be a helpful for people with certain sleep disorders such as insomnia, it is not an ideal approach.  Some call it a ‘band aid approach’. In fact, many sleep issues can be improved with simple dietary changes.

How can my diet affect my sleep?

When our bodies are in a state of homeostasis, this means that all of our biological systems are functioning in equilibrium with each other. Homeostasis is the optimal state for anyone to live in, and when your body isn’t functioning at its best, it can be hard to get a good night’s sleep. Unfortunately it’s quite difficult to maintain homeostasis in the world we live in.

Poor diet, pollution, inactivity, and many other factors contribute to an imbalance of our body’s natural enzymes and neurotransmitters (those little chemicals that activate the receptors in our brain cells to modulate our body’s systems) and our ability to metabolize and process nutrients.

The best way to maintain homeostasis to eat a healthy diet, regular exercise, and adequate good quality sleep. However, if you’re experiencing sleeping difficulties, it’s quite possible that you’re deficient in a select few nutrients.

Which sleep disorders can be improved with good nutrition?

There are many sleep disorders, many nutrients, and a substantial amount of variance among individuals.  This means that these suggestions can’t guarantee that your sleep problem will be improved – but very likely, you’ll be much healthier!

  • If you suffer from non-restorative sleep, you may be deficient in calcium, vitamin C, or simply dehydrated. You may also have a diet that contains too much fat or cholesterol, or an excess of butyric acid.
    • Citrus fruits contain high amounts of vitamin C
    • Dark leafy green vegetables contain significant amounts of readily-absorbed calcium
    • Rancid butter is a source of butyric acid – make sure your butter’s not expired!
  • If you suffer from somnolence (excessive tiredness) you may be consuming excessive calories or fat – or not enough. Don’t start dropping calories from your diet, unless they come from non-nutritional sources like junk food, before consulting your doctor.
  • If you have sleep apnea, and are not overweight (the condition is often present in those who are obese) then you might need to seek medical help. If you are overweight, try to implement a regular exercise routine.  Untreated sleep apnea, particularly when moderate or severe, is associated with an increase in drug resistant hypertension, stroke, irregular heart rhythms and motor vehicle accidents.
    • Sleep apnea disturbs the quality of your sleep and can make it difficult for you to find the energy to exercise. Changing your diet to include more fruit and vegetables should help provide more energy..
  • If you simply sleep too long or too little, quite a few nutrients could be the culprit.
    • People who sleep less than five hours a night have been shown to be low in folic acid, phosphorous, zinc, and selenium, as well as being dehydrated.
    • Long sleepers are indicated to be low in choline, selenium, lycopene and phosphorous, and typically consume more alcohol than shorter sleepers.


Dietary tips to improve your quality of sleep

These tips and tricks may not eliminate a sleep disorder, but they can help improve your night’s rest.

  • Spicy foods and dairy: can cause indigestion, which can make it difficult to fall asleep at night. Indigestion also negatively impacts the quality of the sleep that you do get.
  • Eating a big meal at night, a common approach in the west, is not ideal for your sleep schedule.  Your body will be busy trying to digest your large evening meal which can impact the quality of your sleep.
  • Consuming carbs, sugar, or caffeine within a couple hours of going to bed can keep you up tossing and turning. They stimulate neurotransmitters that are responsible for promoting wakefulness.
  • Drinking alcohol might knock you out, but a drunk sleep (passing out) is not a good sleep. Alcohol commonly changes the sleep architecture so that the ideal restorative benefits of a good night’s sleep are not realized.  More specifically, on nights when alcohol is consumed, individuals commonly wake up after the alcohol has been metabolized and will have difficulty returning to sleep.

The best nutrients for people with sleeping issues

The following nutrients and antioxidants have been shown to help promote healthy sleep:

  • Lycopene is a powerful antioxidant typically found in fruits or vegetables that are red, like watermelons, guavas and papayas.
  • Folate is found in leafy greens as well as avocados and legumes.
  • Phosphorous can be found in tofu, nuts and seeds and legumes.
  • Selenium is best found in whole grains
  • Vitamin D is best found outside your window! If you don’t live in a sunny area, whole grains, mushrooms and fish are other good sources.
  • Vitamin C is found in many of fruits and vegetables from leafy greens to sweet apples and oranges.
  • Choline is an important neurotransmitters that’s best obtained from lean meat, fish and dark leafy green veggies.

The bottom line:

A diet rich in plant based whole foods such as fruits, vegetables, grains and legumes can help restore homeostasis and decrease bodily inflammation and disease.  Along with regular exercise and good sleep, one can better achieve optimal health.  The pillars of good health are diet, exercise and sleep.

Personal note:

For years, I have followed a plant based whole foods diet, also known as a vegan diet.  There is substantial evidence this decreases the likelihood of cardiovascular disease and some cancers.

However, one should be aware that a vegan diet can be very unhealthy particularly if one consumes simple sugars and processed foods.  For me, being a vegan feels right for health, environmental and ethical reasons.

Does sleep protect us from illness?

We have all heard that getting more sleep decrease the likelihood of getting sick?  On the flip side, we know that illness commonly makes us tired but does sleep help us recover quicker?  By examining the medical literature, this blog post will attempt to answer these questions.

It is no secret that sleep rejuvenates our bodies and is essential for proper body functions.  For many years, the effect of sleep on the immune system was largely criticized and considered far-fetched. However, in recent years, many studies have investigated the relationship between a good night’s sleep and the effect it has on the immune system of the body. Although the literature does not define an exact mechanism for enhanced immunity associated with sleep, the evidence of a connection is quite clear.

The Immune System

Before discussing the studies, a primer on immunity is needed.  Our immune system protects our bodies from a disease and infection. It is triggered by a harmful stimulus or stress, which causes increased production and growth of the immune cells.  This system consists of a range of immune cells that protect the body from harmful antigens. The major cellular components are white blood cells (or leukocytes). Some of the white blood cells also produce protein based substances called cytokines which play an integral part in the immune response.

Cytokines are further classified in many subtypes. One of the types of classification divides cytokines into pro-inflammatory cytokines that include Interleukin-1 and Tissue Necrosis Factor (TNF), and anti-inflammatory cytokines that include Interleukin-4, Interleukin-13 and Interleukin-10.

All of the mentioned immune components can be affected by sleep and sleep loss.  In our discussion of the relationship between sleep and immunity, we will explore these cell types and mediators.

The Effect of Sleep on the Immune System

Now that we have discussed the different types of immune cells, we will consider how the individual component is affected by a good night’s sleep.

In a study conducted by Uthgennannt [2] and Schoolmann, 13 healthy men were asked to spend two nights in the sleep laboratory. Lights out was 11 pm and the subjects were allowed to sleep for 3.5 hours. They were then asked to stay awake till 7 am, when blood was sampled. In another condition, the subjects were asked to stay awake between 11 pm and 3 am and then permitted to sleep for 3.5 hours. Blood was sampled every 30 minutes.  In the first condition, when the subjects were allowed to sleep at night, there was a decreased amount of pro-inflammatory cytokines, TNF-alpha and Interleukin-1, while opposite results were observed for those who stayed awake.

In other studies, the serum level of Interleukin-7  which is involved in the maturation and migration of immature T-lymphocytes was observed to increase during the Slow Wave stage of sleep, with a subsequent rise in naïve T-lymphocytes themselves. [1]

Another study conducted by Matsumoto [5], on a 24-hour wake period, demonstrated a marked decrease in cytotoxic NK cells, important cells of inflammation.  In addition, there was a decrease in anti-inflammatory cytokines such as Interleukin-10.

Although the levels of cytokines fluctuate, and the exact pattern is pretty complex; in a nutshell, the main pro-inflammatory cytokines decrease during nocturnal sleep (usually in Slow Wave Sleep stage), whereas the levels of T-lymphocytes and cytokines that are involved in the growth and differentiation of T-lymphocyte as well as those that take part in adaptive immunity (more later) increased. This reflects that sleep, indeed, has a positive effect in boosting the immunity of our bodies since it allows for some cells and cytokines to peak levels while keeping other components at bay.

Another aspect of immunity that is theorized to enhance during sleep is the formation of immunologic memory. Normally when a person is infected by a particular pathogen, immune cells memorize the response.  By forming antigen specific antibodies, the body reacts more rapidly to any subsequent attacks by the same pathogen. Studies have revealed that subjects who stayed awake after a hepatitis A vaccine shot demonstrated lower levels of antigen-specific antibody titers compared to those who received the vaccine and slept regularly [1]. This proves that not only does sleep help in enhancing the cellular elements of the immune system, but it also helps in the formation of immunologic memory.

Adaptive Immunity vs. Innate Immunity

Numerous studies have established that sleep has a direct effect on adaptive immunity, and less so on innate immunity.

Innate immunity involves the protection against a foreign antigen by the body’s defense mechanisms that do not include the antigen-specific immune cells. These defense barriers include the skin, chemicals in the body and cytotoxic immune cells. Adaptive immunity is more complex and encompasses the reaction of antigen-specific immune cells which includes recognizing the antigen, releasing a cascade of immune cellular components and mediators, and finally removing the pathogen.

Research on the decreased levels of Interleukin-6 during sleep which acts as both a pro-inflammatory and anti-inflammatory agent and takes part in innate immunity suggests that innate immune response is less affected during sleep. Similarly, the serum level of interferon-alpha that plays a core role in the innate immune response against viral infection also declined during sleep. On the other hand, Interleukin-7, an important mediator of adaptive immunity, showed a marked increase during sleep. [6]

The Effect of Prolonged Wakefulness on the Immune System

While inflammation is an early response to infection, an inflammatory response unchecked can be detrimental. Several studies have looked at the relationship between sleep deprivation and immunity. The results of these studies were fairly consistent that the levels of the immune cells were impacted by sleep quantity.

Blood samples from individuals subjected to prolonged wakefulness showed a marked increase in inflammatory mediators such as interleukin-6 levels, pro-inflammatory cytokines, TNF-alpha, interleukin-1 and C-reactive protein [7] An increase in these pro-inflammatory cells made the subjects more vulnerable to stress. In addition, the elevated levels of these inflammatory markers is associated with cardiovascular disease and type 2 diabetes. [1]

Does Sleep Decrease the Likelihood of Getting Sick?

Although the relationship between sleep and immunity is still being researched, many studies indicate a strong relationship between a proper sleep/wake cycle and improved immunity of the body.  There is little doubt that a good night’s sleep can decrease the likelihood of getting sick.



  1. Besedovsky, Luciana, Tanja Lange, and Jan Born. “Sleep and immune function.” Pflugers Archiv. Springer-Verlag, Jan. 2012.
  2. Uthgenannt, D., D. Schoolmann, R. Pietrowsky, H. L. Fehm, and J. Born. “Effects of sleep on the production of cytokines in humans.” Psychosomatic medicine. U.S. National Library of Medicine, n.d.
  3. Sarosh J. Motivala, Michael R. Irwin. “Current Directions in Psychological Science”Vol 16, Issue 1, pp. 21 – 25, June 24. 2016
  4. Dinarello, C. A. “Proinflammatory cytokines.” Chest. U.S. National Library of Medicine, Aug. 2000.
  5. Matsumoto Y, Mishima K, Satoh K, Tozawa T, Mishima Y, Shimizu T, Hishikawa Y. Total sleep deprivation induces an acute and transient increase in NK cell activity in healthy young volunteers.Sleep.2001;24:804–809.
  6. Dimitrov S, Lange T, Nohroudi K, Born J. Number and function of circulating human antigen presenting cells regulated by sleep.Sleep.2007;30:401–411
  7. Meier-Ewert HK, Ridker PM, Rifai N, Regan MM, Price NJ, Dinges DF, Mullington JM. Effect of sleep loss on C-reactive protein, an inflammatory marker of cardiovascular risk.J Am Coll Cardiol.2004;43:678–683.

Sleep and Memory

For many years, scientists have been trying to understand the connection between sleep and memory. A multitude of research, experiments and studies have been conducted for this purpose, however the underlying mechanism of this connection is still a question mark. Although there is no clear mechanism by which sleep affects our memory, there is no denying that the two are interrelated.

Before we jump into the theories that have been proposed by researchers on this topic, we first need to be familiar with the different types or stages of sleep, as well as the types of memories first.

SLEEP: REM vs. Slow Wave Sleep

Relative to sleep, we need to better understand 2 of the 4 stages of sleep: Rapid-eye-movement (REM) and Slow-Wave Sleep, also known as deep sleep. The two stages occur alternatively with marked changes in the brain waves. The characteristics of deep sleep as seen on an EEG are high amplitude and low frequency brain waves and deep sleep tends to occur more towards the beginning of the night. Dreaming in this stage is rare, and if dreaming does occur, it is usually forgotten once you wake up.

REM sleep, on the other hand, predominates in the second half of the night as the body becomes more and more rested. True to its name, REM sleep is characterized by muscles twitches and eye movements as well as vivid dreaming. Brain waves on the EEG during REM sleep show low amplitude, high frequency waves.

MEMORY: Declarative vs. Non-Declarative

Long-term memory is broadly categorized in two forms: Declarative and non-Declarative. One basic difference between the two forms is whether or not the hippocampus is involveda part of the brain’s limbic system) is involved or not. [1] Declarative memories encompass those that can be easily recalled and consist of the knowledge of facts and events, involving visual and verbal input. Declarative memory itself is divided into semantic memories, the knowledge of facts and world events, and episodic memories that store more personal, autobiographical information. Neuronal circuits in the hippocampus are an integral part in the formation of declarative memories.

Non-declarative memories, also sometimes referred to as procedural memories, are those that store a person’s memory of a skill. [3] This includes all types of ‘how to do’ memories such as cooking a particular dish or playing the piano. Unlike the former type, non-declarative memory does not involve the active participation of brain cells in the hippocampus; instead, motor areas in the frontal cortex are involved.

Memory Processing During Sleep

The process of memory formation isn’t as simple as it might seem. While a lot is still unknown about how memories are truly processed in our brains, we do know the process takes place in three core stages: Acquisition, Consolidation and Recall. [1]

The introduction of a particular memory in the brain is known as acquisition. The consolidation stage occurs after the memory has been introduced when it gets further sorted and stored (or consolidated). Finally, the recall process is simply recalling or remembering a stored memory.

Clinical experiments on rats and humans have demonstrated a possible relation between sleep and the consolidation of memories. Acquisition and recall, on the other hand, take place when the person is wide awake. It is hypothesized that one you fall asleep, the acquired memories become consolidated and stored in their final destination. Not all memories are stored in the same area of the brain. According to Dr. Robert Stickgold of the Sleep Department at Harvard, the memory of what you ate for breakfast yesterday is not stored in the same area of the brain where the memory of what your favorite breakfast is stored. It is when you fall asleep that these memories are sorted into their respective places. [3]

A primary question relative to sleep and memory is during which stage of sleep are memories actively processed.  Although a definitive pathway has not been elucidated, studies have suggested a relationship between consolidation of memories (especially the non-declarative type of memory) and REM sleep.

In a recent research study, subjects who were asked to learn a foreign language demonstrated increased periods of REM sleep during the night. [3]  As far as declarative memories were concerned, none of the studies could prove the connection between verbal/visual memories and REM sleep.

This led to the hypothesis that perhaps Slow Wave Sleep had some role in the consolidation of memory, particularly the declarative type. Research is still scarce concerning this theory and the studies that have been conducted show inconsistent findings.

Effects of Sleep Deprivation on Memory

The effect of sleep deprivation on an individual’s memory is a topic that has been explored extensively. Many studies have been conducted where subjects were kept awake for over 35 hours to test the effect sleep deprivation had on their long-term memory. Results showed that a 24-hour sleep deprivation period did not have a significant effect on memory recall.  However, a 35-hour sleep deprivation period results in impaired facial recognition (a type of episodic memory), recall and verbal memory. [3]

Although a relationship was established between sleep deprivation and memory through these studies, we still do not know if it was sleep deprivation that directly affected the neuronal circuitry involved in memory consolidation, or if the effects were more metabolic.

As pointed out in a post in Harvard Health Publications, the effects of too little sleep on memory impairment could be due to other known harmful effects of sleep deprivation on the heart and circulation. Sleep deprived patients usually have a consistent high blood pressure that could directly affect brain cells that consolidate memory. [4]

Improving Memory with Sleep

Several researchers have hypothesized that obtaining the recommended hours of sleep can benefit the individual’s memory. To test this hypothesis, a study was conducted on a group of twenty female and twenty male adolescents, between 10 and 14 years. The group was divided into two – a sleep group, and a non-sleep group. All subjects were given the paired-associate test, a standard for testing declarative memory. The paired-associate test consists of remembering two related (tree/leaf) and two unrelated (tree/shoe) words. In addition, the two groups were given the letter-number test which consists of sequencing a list of mixed numbers and letter in an ascending order.  The sleep group was given the task at 9 pm and was tested at 9 am after a night of sleep. The non-sleep group was given the task at 9 am and tested at 9 pm at night with continuation of normal day activities and without naps. The paired-associate test did not result in any significant differences.   However, utilizing the letter-number test, there was a 20.6% increase in long term memory in the sleep group showed versus the non-sleep group. [5]

Even though the direct effect or mechanism of sleep on memory is still being studied, it is clear that improves cognition and refreshes the body. Therefore, a good night’s sleep is essential for optimal functioning through the day.  Obtaining 7-8 hours of sleep nightly at a consistent time along with proper diet and exercise can greatly contribute to a great night’s sleep.


  1. Rasch, Björn, and Jan Born. “About Sleep’s Role in Memory.” Physiological Reviews. American Physiological Society, Apr. 2013.
  2. Alhola, Paula, and Päivi Polo-Kantola. “Sleep deprivation: Impact on cognitive performance.” Neuropsychiatric Disease and Treatment. Dove Medical Press, Oct. 2007.
  3. “Sleep, Learning, and Memory.” Sleep, Learning, and Memory | Healthy Sleep. N.p., n.d.
  4. LeWine, M.D. Howard. “Too little sleep, and too much, affect memory.” Harvard Health Blog. N.p., 29 Oct. 2015.
  5. Potkin, Katya Trudeau, and William E. Bunney. “Sleep Improves Memory: The Effect of Sleep on Long Term Memory in Early Adolescence.” PLoS ONE. Public Library of Science, 2012.