The hypothalamus, a peanut-sized structure deep inside the brain, contains groups of nerve cells that act as control centers affecting sleep and arousal. Within the hypothalamus is the suprachiasmatic nucleus (SCN) – clusters of thousands of cells that receive information about light exposure directly from the eyes and control the behavioral rhythm. The brain stem, at the base of the brain, communicates with the hypothalamus to control the transitions between wake and sleep. Sleep-promoting cells within the hypothalamus and the brain stem produce a brain chemical called GABA, which acts to reduce the activity of arousal centers in the hypothalamus and the brain stem. The brain stem (especially the pons and medulla) also plays a special role in REM sleep.
Multiple interacting neurotransmitter systems in the brain stem, hypothalamus, and basal forebrain converge onto common effector systems in the thalamus and cortex. Sleep results from the inhibition of wake-promoting systems by homeostatic sleep factors such as adenosine and nitric oxide and GABAergic neurons in the preoptic area of the hypothalamus, resulting in large-amplitude, slow EEG oscillations.
In summary, the hypothalamus and brain stem are the key parts of the brain that control the sleep/wake cycle. The hypothalamus contains the suprachiasmatic nucleus (SCN), which receives information about light exposure and controls the behavioral rhythm. The brain stem communicates with the hypothalamus to control the transitions between wake and sleep, and sleep-promoting cells within the hypothalamus and brain stem produce GABA, which reduces the activity of arousal centers. Multiple neurotransmitter systems in the brain stem, hypothalamus, and basal forebrain converge onto common effector systems in the thalamus and cortex to regulate sleep and wakefulness.
