Sleep and the EEG

When the EEG, or electroencephalogram, was invented, a whole new world opened for  exploration — the previously unknown world we all enter when we fall asleep.

Before the EEG, sleep was often thought of as a death-like experience, wherein one loses consciousness each night, hopefully to return in the morning.  Our remembered dreams gave us glimpses of this other world, often comprised of bizarre fantasies and sometimes disturbing nightmares, but no one knew for sure what was going on.

By measuring electrical activity in the brain, the EEG gave us a much better understanding of this unknown world.  The brain — powered by billions of neurons, or brain cells — produces measurable waves of electricity the EEG can record.  The first recording EEG machine was invented by German physiologist and psychiatrist Hans Berger in 1924.

Yet it would be almost 30 years later before scientists got the bright idea of attaching one of those devices to someone while asleep.  In 1953, two researchers at the University of Chicago, Eugene Aserinsky and Nathaniel Kleitman, first measured the alternating periods of REM (rapid eye movement) and NREM (sometimes called slow wave sleep) during all-night EEG recordings, launching the era of modern sleep research.

More than 60 years later the EEG remains the primary tool for laboratory sleep evaluation, and what researchers find looks something like this:

stages-of-sleep-eeg1

EEG recordings for various stages of sleep.  Notice the similarity between REM sleep (bottom) and an awakened state (top), and the striking difference between that and the slow deep rhythmic waves of Stages 3 and 4, the deepest forms of sleep.

When we fall asleep we transition through various stages, starting with a relaxed state, which leads to drowsiness, or Stage 1.  True sleep starts in Stage 2 with the appearance of the sleep spindles and K complexes, and the deepest form of sleep shows rhythmic waves of electrical activity slowly sweeping across the brain.

The transition of sleep stages usually ends with something that appears very close to an awakened state — the REM dream stage.  A complete cycle of NREM and REM usually takes about 90 minutes, and we typically experience 4 to 6 complete cycles of sleep each night.

Research has shown during these deepest slow wave sleep stages the brain clears itself of toxins and replenishes its energy supply for a new day.  It is thought these slow cycles of electricity literally draw cerebrospinal fluid into and through the brain to facilitate this renewal process.

If awakened during a deep NREM stage, we usually remember little about our dreams and are typically extremely groggy.  In complete contrast the REM dream stage is much closer to a fully awakened state.  In REM our dreams are vivid, and by completing one’s final REM stage of the night one likely feels better rested and more emotionally restored for a new day.

Use of the EEG opened a much broader understanding of sleep, with intense research still ongoing today.  There is still much more that we don’t know than we know about this hidden world we enter each night.

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