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Chapter 2 – An Overview of Normal Sleep

Sudhansu Chokroverty


The history of sleep medicine and sleep research is a history of remarkable progress and remarkable ignorance. In the 1940s and 1950s, sleep had been in the forefront of neuroscience, and then again in the late 1990s there had been a resurgence of our understanding of the neurobiology of sleep. Sleeping and waking brain circuits can now be studied by sophisticated neuroimaging techniques that have shown remarkable progress by mapping different areas of the brain during sleep states and stages. Electrophysiologic research has shown that even a single neuron sleeps, as evidenced by the electrophysiologic correlates of sleep-wakefulness at the cellular (single-cell) level. Despite recent progress, we are still groping for answers to two fundamental questions: What is sleep? Why do we sleep? Sleep is not simply an absence of wakefulness and perception, nor is it just a suspension of sensorial processes; rather, it …