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Why is Deep Sleep Important?

A 54-year-old woman came into my office the other day to talk about her sleep problems.  She was distraught.  Her eyes were heavy.  She looked fatigued and anxious.  She spoke slowly and tried to concentrate on what she was saying, although it took great effort.  She had been through some difficult times.  Years ago, she’d had to assume an increased responsibility for her family after losing a family member.  She told me she started having trouble sleeping around that time. More recently her mother passed away, leaving her even more at a loss, stricken with grief.  She just couldn’t get the sleep she felt she needed anymore.

“Doc, I just don’t think I sleep deeply, the way I used to.”

She didn’t sleep “deeply”.

The concept of “deep” sleep seems intuitive when discussed casually.  It refers to a type of sleep that we think of as very sound, without awakenings, and during which we can’t be aroused.  It’s a sleep that we know we get when we wake up feeling refreshed and ready to go about our days, with high energy, full concentration, and great vigor.  It’s the type of sleep that babies get, or at least that’s what we think when observing them.  They’re “out.”  And it’s the type of sleep we tend to get after we’ve been up for days, when we’ve deprived ourselves of sleep for some unnatural reason.  Deep sleep is that sleep that just feels good.   It’s what we want and what we believe we need. Yet, for those who don’t sleep wellwho have insomniait’s something that doesn’t come.

The science of sleep provides some clues as to why “deep sleep” is important.  Scientists generally think of “deep” sleep as that period of sleep when electrical activity in the brain slows down and becomes stages of sleephighly regular.   Sleep is typically broken down into 2 main phases, NREM sleep, which occupies most of the night, and rapid eye movement (REM) sleep.  NREM sleep is thought to be the quieter, more restful part of sleep, and REM sleep is the more active part often filled with emotionally packed dreams.  NREM sleep is further divided into 3 different stages from “lighter” stage 1 to “deeper” stages 2 and 3 sleep, with stage 3 sleep thought to be the “deepest” stage of sleep.

Much attention has been focused on stage 3 sleep as the deepest, most restorative part of sleep. It is this stage of sleep that is increased during the period of recovery sleep following a period of sleep deprivation.  In some sense, it seems to be the brain’s way of rebounding or restoring itself after it’s been deprived.  And, the more one is deprived of sleep, the greater the rebound of stage 3 sleep once an individual is given a chance to recover.  Something important to recovery seems to be occurring at that time.

Studies have also shown that metabolism, or activity in the brain, is lowest during NREM sleep.  For example, in the frontal cortex (the large part of the brain that sits behind the forehead and is considered our “executive” brain) metabolism is very high when we’re awake, solving problems, thinking, remembering, and planning out our lives.  As we go from lighter to deeper stages of NREM sleep, metabolism slows greatly and is lowest in stage 3 sleep, that portion of sleep thought to be the deepest, most restorative portion.

Other physiological signs support that these deep stages of sleep serve some restorative function.  Part of our nervous system, the autonomic nervous system, operates always in the background of our lives without our awareness.  The autonomic nervous system has two basic divisions, the sympathetic system and the parasympathetic system.  The sympathetic nervous system gets into gear when we’re threatened and in danger, activating us to meet an oncoming challenge. The parasympathetic nervous system is more associated with periods of rest and restoration of the body.  Not surprisingly then, it is the parasympathetic nervous system that is more active during these deep sleep periods.

Deep sleep is also that period when there is a surge of growth hormone production.  Growth hormone stimulates growth, cell reproduction, and cell regeneration in humans: another sign that deep sleep is a period of rest and restoration.  Deep sleep is also associated with the laying down of new memories in the brain, laying the foundation for a fuller, more complete life upon awakening.

The amount of deep sleep we can get varies across our lives.  It is highest when we are young and during the teenage years when the brain is maturing, remains relatively stable across young adulthood and mid-life, and then begins to decline in later years.  This aging pattern closely relates to declines in the thickness of the brain cortex across the lifespan.

Finally, deep sleep is more difficult to get when we are going through emotionally challenging periods.  Individuals with clinical depression or anxiety disorders and insomnia tend to suffer in their ability to get deep sleep.  Their brains tend to be more charged and active, if you will, dealing with the challenges they are facing. Unfortunately, the brain simply won’t allowing them to get the rest they need and deserve, preventing from leading fuller, happier lives.

“Yes, I understand you’re not getting deep sleep,” was my reply to my patient. I appreciated the full significance of her statement, and how it was impacting her brain, her health, and her life.  “Let’s see what we can do to help.”


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