Sleepy Head: the science of snooze

Many consider sleep a time when we shut off for a few hours during the night to recover from, and prepare for, activity during the day. Surprisingly your brain and body are remarkably active while you snooze.

Sleep is important to a number of brain functions, including how memories are made. All day nerve cells in our brains (neurons) communicate with each other. As we slumber our brains replay the day’s events, evaluate experiences in order of most importance and establish the sequence in which they took place. It then records and stores the way in which neurons communicated with each other during that day’s experience. A memory of that experience can then be recalled when those neurons are reactivated in the same pattern.

Recent findings suggest that the brain may even be cleaning itself as we sleep.  During non-REM sleep a slow electrical wave pulses through the brain, followed by a drop in the amount of blood in the brain. Cerebrospinal fluid rushes in to fill the space vacated by the blood. This clear liquid moves through large cavities in the lower and central brain washing away harmful toxins that build up during the day.

Today most people are not getting the amount of sleep they need to be healthy. Research has shown that lack of good quality sleep can lead to disorders including high blood pressure, cardiovascular disease, diabetes, depression, and unhealthy weight gain.

Anatomy of Sleep

Several structures within the brain are involved with sleep.

Deep inside the brain the peanut sized hypothalamus controls sleep and wakefulness as the suprachiasmatic nucleus (SCN) receives information about light exposure directly from the eyes.

Located within the brain’s two hemispheres, the pineal gland receives signals from the SCN and increases production of the hormone melatonin, which helps put you to sleep.  

At the base of the brain the brain stem communicates with the hypothalamus to control transitions between wake and sleep. It also sends signals to relax muscles so that we don’t act out our dreams during REM sleep.

During REM sleep the thalamus sends the cerebral cortex the sights, sounds and other sensations that fill our dreams.

The four stages of sleep

During the night we experience two types of sleep, rapid eye movement (REM) sleep (which has one stage) and non-REM sleep (which has three different stages). A sleeper will cycle through all four stages several times during the night.

Stage 1 non-REM 

Period from wakefulness to sleep.

Heartbeat, breathing, and eye movements slow. Muscles relax with occasional twitches.

Brain waves begin to slow from their daytime wakefulness patterns. 

Stage 2 non-REM

Period of light sleep before entering deeper sleep.

Heartbeat and breathing slow. Muscles relax even further. Body temperature drops and eye movements stop.

Brain wave activity slows but is marked by brief bursts of electrical activity.

Stage 3 non-REM

Period of deep sleep.

Heartbeat and breathing slow to lowest levels during sleep. Muscles are relaxed. It is difficult to awaken sleeper. 

Brain waves become even slower

REM sleep

First occurs about 90 minutes after falling asleep. Most dreaming occurs at this stage.

Eyes move rapidly from side to side behind closed eyelids. Breathing becomes faster and irregular. Heart rate and blood pressure increase to near waking levels.

Brain wave activity becomes closer to that seen in wakefulness.

Arm and leg muscles become temporarily paralyzed, preventing sleeper from acting out dreams.

How much sleep do you need?

Sleep needs and patterns change as we age but we spend roughly one third of our lives doing it. 

Babies sleep as many as 18 hours a day, which helps with growth and development (especially of the brain). 

Children and teens need between nine and ten hours of sleep each night.

Adults need seven to nine hours of sleep a night.

Article originally published in Brainspace Magazine

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