WEBVTT

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The scientific study of sleep really began in the 1950s, as researchers applied new techniques of physiological recording to sleep research.

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Scientists discovered that aspects of the body's activity could be directly measured by mechanical devices that produce electrical signals in response to physiological fluctuations.

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These signals could be fed into a physiograph, which amplified the signals and recorded them for later analysis.

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In this way researchers could record changes in heart rate, breathing rate, and muscle tension during a night of sleep.

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But the real breakthrough came when researchers discovered that the brain itself gives off weak electrical signals,

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generated by the simultaneous firing of millions of neurons within the brain.

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Electrodes placed on the scalp can detect these signals.

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When the signals are amplified and fed into a special type of physiograph called an electroencephalograph (EEG),

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scientists can obtain a permanent record of the activity of the brain across an entire night of sleep.

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Note that this record doesn't tell us what the person is thinking, or what any individual neuron is doing, but merely how active the brain is at each moment.