Sleep: What it Does

Why sleep and why dream? Why do some of us insist they do not just because they cannot remember what they dreamed? How does sleep apnea fit into the functions of dreaming?

National Public RadioSleep apnea is reported in Eight Is Too Much For ‘Short Sleepers’, (Saturday Weekend Edition 16 April 2011). So why is apnea more likely in those who get what has been called the recommended amount of sleep? The real functions of sleep and dreaming might explain how damage elsewhere in the body could be responsible for sleep apnea. The amount of sleep that a person needs might demand a more complex study than just its association with apnea. There may be better tests of hypotheses which could determine how short sleepers are different from long sleepers.

Updated: 08 Aug 2016

Sleeping Baby from New Baby and You,


A team of scientists at the University of California at San Francisco found an association between certain genetic mutations and a propensity toward ‘short sleeping’, where people routinely sleep only four to six hours a night and seem to function as well or better than those who needed longer sleep times. They found that short sleepers tend to be very active, have faster metabolisms, to be thinner, are more energetic, have more positive attitudes, and a higher tolerance for pain than the ‘long sleepers’.

Problems With This Study

The following questions were not addressed in this report: Is there a difference in longevity of five-hour sleepers from eight-hour sleepers? Are five-hour sleepers more likely to suffer ill health either throughout their lives, or at the ends of their lives? Or are they in overall good health all the time? Are there differences in daily activities each group engages in or a difference in the incidence of risky behaviors? Do most children sleep through the night without awakening, even for a few minutes, thus breaking up a typical night into two or more sleep periods?

As to people who need only five hours of sleep–this condition is not unknowable. Dr. Fu needs to concentrate on something this short-sleeper, Elena Angeli, said in her interview–that she needed only 5 1/2 hours of sleep and she felt energized. There may be a peak in body energy in all sleepers, available after only five hours of sleep. The extra three hours the normal sleepers “need” may show that they use that energy during sleep for something else.

The Sleep Cycle

In order to figure out what someone might feel better with a shorter sleeping period, one needs to understand the sleep cycle. Because of its “restful” association, most people ascribe to it a “low energy-consuming” and “restorative” role. Thus, metabolic process may be explained by a discussion of the physiology of sleep.

7 Stages of Sleep, as seen in EEGs, from Wikimedia

The sleep cycle has been described as having at least five stages, including a very brief beginning period of light sleep characterized by rapid eye movement, and other muscle responses. It is followed by three or more stages, with successively increasing amounts of slow-wave brain activity, leading to a very “deep sleep” by the fourth stage. The cycle ends with the REM (Rapid Eye Movement) stage. Dreaming is most reported during the REM stage, although a person may dream as well during the first stages of NREM.

The first four stages are often called NREM (or “non-REM” stages) because rapid eye movements are generally lacking. Unlike that first stage of brief and often jerky muscle responses, the person in the REM stage is generally described as immobile, thus this stage is called “paradoxical sleep.” A typical sleeping period of five to ten hours is made of several such cycles.

Energy Consumption During Sleep

The brain uses glycogen for energy and, as such, this chemical is often the target of brain metabolism studies. Fluctuations in brain glycogen levels during sleep have been observed. It is generally depleted during REM sleep and increased in the neocortex during NREM sleep. In order to explain these fluctuations, researchers have proposed that the sleep cycle may regulate glycogen metabolism in a state of “brain energy conservation” (the Bennington-Heller Hypothesis).

The “glycogenetic hypothsis” attempts to explain the fact that most of the glycogen used by the brain during sleep is actually produced during the wakefulness period, just before sleep sets in. The Bennington-Heller hypothesis depends upon the assumption that the brain controls its own sources of glycogen. Petit et al. (2015) found that there were fluctuations in glycogen during periods of both wakefulness and sleep, but showed that there was little experimental support for the role of sleep in glycogen regulation. However, they pointed out that the depletion of glycogen during dreaming was still not explained.

The Functions of Sleep

Taking a larger view of sleep may explain this link. One can argue that a major role of sleep may be the repair of damaged tissues in the brain and the rest of the body. A step back first demands more understanding of the nitty gritty.

This hypothesis might explain why there is a greater influx of glycogen in the neocortex during the period of slow-wave activity characteristic of NREM stages, and a decrease in glycogen presence during REM activity. If sleep serves a restorative function, as some have described, it stands to reason that repair of damage in the brain and body might take place during sleep. One can reasonably hypothesize that repairs in the brain are done during the first four stages of sleep (slow-wave period), and the repaired circuitry is tested during last stage of sleep (REM). Different areas of the brain will be repaired and then tested during the course of a day’s sleeping period. Some of that glycogen depletion has also been seen during awakening from a period of sleep.

It can also be hypothesized that this repair cycle depends upon levels of consciousness to test the repaired circuitry, causing some testing to continue into the period which occurs upon awakening just after a REM stage. The act of testing circuitry might demand greater amounts of glycogen than the repairs performed before then.

Evidence for Energy Role in Sleep

Whole sections of the brain reduce their activity during sleep, but not the whole brain at once. For instance, stress chemistry is shut down, along with the amygdala during REM sleep. Although areas distributed throughout the brain have been identified, the strongest reduction in cerebral blood flow in a PET scan (indicative of reduced activity) during NREM sleep was seen in the prefrontal and inferior parietal cortices, midbrain, thalamus, and basal ganglia. Some areas showed increased activity, e.g. the striate cortex and mid-temporal lobe. There appears to be maintenance of some low-level sensory but not high-level sensory processing ability during NREM sleep.

Even during REM sleep, greater activity is seen in non-neocortical than in neocortical areas, especially ventral brainstem (associated with the reticular activating system), although the medial prefrontal cortex, visual and auditory association areas did show increases in blood flow. The only cerebellar structures showing an increase in activity during REM sleep was the vermis, associated with the vestibular system which plays a major role in rapid eye movements and inhibition of contraction of other muscles.

But isn’t dreaming associated with greater conscious processing? The connection between thalamus and neocortex is altered during the sleep cycle so that the person is not fully conscious during sleep. However that coupling is enhanced during REM sleep, and fully activated during wakefulness. Lucid dreaming, where a person knows they are dreaming but is still capable of a dream state of mind, may reflect a thalamo-neocortical connection level that is somewhere in between normal REM sleep and the fully conscious, awake state.

Although not detailed, the researchers also detected differences between cerebral hemispheres as well, but significant differences were rarely detected.

'The Sweet Dream the Ago" by Antonio García Vega, at Wikimedia,

But Why Dream at All?

It stands to reason that dreaming is a critical function in the brain. Indeed, it has been associated with memory processing and consolidation, learning, emotional adaptation and mood regulation. Hobson (2009) concludes that it is a purely biological phenomenon, serving only physiological functions and acts to prepare the brain for the realities of the physical environment the body needs to face upon awakening.

It is proposed here that it is possibly used to make repairs. The short sleepers either do not need the extra three hours for repairs in the body, or cannot make the repairs in the body when the brain is needed to direct them.

The fact that many people do not even remember dreaming may give clues to its function.  Since the brain must repair itself and directly repair the rest of the body when local repair mechanisms aren’t working, dreaming may allow the brain to use semi-conscious thought patterns to find damage and repair it.  If one awakens and does not remember any dreams, one can reasonably suspect that the brain has performed its function completely and doesn’t need the awake, fully conscious thinking processes to help it finish its repair processes, guided by the thought patterns one has upon awakening and remembering a dream.

There are two functions of sleep–to restore glycogen levels in the brain for maintenance and repair, and repair of damaged tissues in the rest of the body.  Thus, there are two areas that generally need repair at night: brain and rest of body.  One can reasonably hypothesize that repairs in the brain are done during the first 5 hours of sleep and repairs in the body during the last 3 hours of sleep, or just upon awakening, depending upon the extent of repair needed.

Dreaming occurs when the brain is shutting down whole sections to renew glycogen stores. It stands to reason that dreaming is a critical function in the brain, possibly used to make repairs.  The short sleepers either do not need the extra three hours for repairs in the body, or cannot make the repairs in the body when the brain is needed to direct them.

The first five hours of sleep may be dedicated to repair in the brain.  That “extra” three hours of sleep may cause the production of signals in the brain that promote repair in damaged tissues in the rest of the body.  Comparisons between five-hour sleepers and eight-hour sleepers should be done where Dr Fu examines the viability of different tissues in the rest of the body before sleep and after awakening to see if that tissue function has been “rejuvenated” or not.

Simple physiological tests can be done with fMRI to determine where in the rest of the body there seem to be tissues not working that should be, e.g. damaged muscle fibers, parts of the kidney, etc. Damaged tissue may never light up during these tests, so instead of looking for areas in the brain and body for areas that do light up, you can look for those that don’t.  This method doesn’t find all areas that are damaged, but can identify those that do not ask for blood flow all, but theoretically should during these tests. There may be a lot of places where minor damage can be seen on an MRI but do not seem to impair the functioning of the person.  Simple volumetric measurements of the non-functioning tissue can be done before and after fMRI + appropriate activity to determine if there is any change in the activity of tissues.

There can be three outcomes to any of these comparisons:

  1. There is no difference in volumes of damaged tissue areas of before/after the tests in either the five-hour or eight-hour sleepers.
  2. The five-hour sleepers have all damaged areas repaired during sleep or just after awakening.
  3. The five-hour sleepers do not repair all damaged areas during sleep or upon awakening, but the eight-hour sleepers do.

Interpretations are obvious: With results as in

  1. Investigators are still “in the dark” about why some people can get by with five hours of sleep and some people cannot. The answers may come from asking some of the questions raised in this post.
  2. Either the five-hour sleepers do not damage as much tissue during the waking hours as eight-hour sleepers do, or the five-hour sleepers are much more efficient at doing the repairs, either in the brain and thus in the body, or in the body alone.
  3. Five-hour sleepers for some reason cannot direct the brain to do repairs in the body but eight-hour sleepers can. In this last case, although five-hour sleepers seem to be able to do more in a day, seem more efficient, they may have a shorter life, or more health problems later in life (all of which must be verified with questionnaires or long-term studies).

For more of my comments on sleep apnea, see the following postings:
Surgical Approach to Sleep Apnea
Treating Sleep Disordered Breathing in Kids


Image of sleeping newborn taken from:
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