Contenu
In the last few decades, scientists have discovered that far from being a time of neural silence, sleep is characterized by complex patterns of electrical, neurochemical and metabolic activity in the brain. At the level of the electroencephalogram (EEG), the states of rapid-eye-movement (REM) and non-REM sleep are accompanied by massive changes in the activity of millions of neurons, resulting in widespread changes in neural excitation, as well as rhythmic waves of activity. Functional brain imaging has shown unusual changes in brain metabolism that accompany sleep onset and the descent into the deeper stages of sleep. These mysterious patterns of EEG activity and metabolism are paralleled by equally mysterious changes in the behavior of single neurons and non-electrical brain cells, known as glia, and changes in gene expression that are starkly different than what is observed during wakefulness. Understanding how and why these events occur in the brain may one day provide an answer to an even deeper mystery: Why do we sleep?