Sleep oscillations and their blockage by activating systems.

There are three major oscillations in thalamocortical systems during the state of sleep with synchronization of the electroencephalogram: 1. Spindles (7 Hz to 14 Hz) are generated in the thalamus at sleep onset and are blocked during arousal or rapid-eye-movement sleep by cholinergic systems that decouple the synchronizing network of the reticular thalamic nucleus. 2. Delta potentials (1 Hz to 4 Hz) appear during late stages of electroencephalogram-synchronized sleep. At the thalamic level they are produced by the interplay between two intrinsic currents of neurons with cortical projections. Delta rhythm is suppressed by cholinergic and noradrenergic systems. 3. A slow oscillation (< 1 Hz) is generated in the cerebral cortex and has a pivotal role in grouping the thalamic-generated sleep rhythms within wave-complexes recurring periodically, every two to five seconds. The slow rhythm is blocked by cholinergic and noradrenergic projections. Sleep rhythms consist of long-lasting inhibitory components that obliterate synaptic transmission and disconnect the brain from the outside world.