Trivia Junction

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And you thought sleep was restful

Until the late 1950s, the dominant view was that sleep was simply an idling state. However, electroencephalograms (EEGS), which record fluctuations of electrical activity in groups of nerve cells in the brain, have shown that the sleeping brain is active and that sleep is composed of identifiable stages that occur in cycles throughout the night.

About 30 to 45 minutes after falling asleep a person enters slow wave sleep, which is characterized by low frequency brain waves. As a sleeper progresses through stages one to four of slow wave sleep, the EEG records brain waves that are of progressively lower frequency and higher voltage.

The muscles are relaxed during slow wave sleep, but the sleeper shifts posture regularly. Heart rate and blood pressure decrease. Stage four sleep is the deepest and most difficult to interrupt. Someone awakened from stage four sleep feels groggy and confused.

By about 90 minutes after the initiation of sleep, the sleeper has progressed back through stage four to stage one of slow wave sleep, and the EEG pattern changes abruptly. The EEG records low voltage, high frequency brain waves, similar to those observed in the waking state. This is rapid eye movement or REM sleep, and if awakened, most sleepers will recall dreaming. Sleepers awakened from slow wave sleep may recall an image or emotion, but rarely a storylike dream.

The pons, an area at the base of the brain, keeps the body in a state of paralysis throughout REM sleep, though the muscles controlling eye movements and respiration are not inhibited. During REM sleep, the body even ceases to regulate its temperature.

Cats with damage to the pons appear to act out their dreams, for example, stalking and pouncing as if they were chasing mice. People can also have REM behavior disorder. One sleeper, who had been dreaming he was a football player charging an opponent, woke up with a gash on his head from tackling his dresser.

Depriving people of sleep right after they are trained to do a task interferes with learning, even when people are tested a week later. Brain-imaging studies with animals reveal that the pattern of brain activity occurring during the learning of a task is replayed during sleep. The more often the pattern is replayed during sleep the greater the learning.

The exact mechanisms through which sleep facilitates learning and memory are not understood. However, certain genes known to play a role in changing connections between nerve cells are switched on in the brain during sleep.

© Sherry Seethaler

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