SLEEP AND AROUSAL - THALAMOCORTICAL MECHANISMS

Thalamocortical activity exhibits two distinct states: (a) synchronize d rhythmic activity in the form of delta, spindle, and other slow wave s during EEG-synchronized sleep and (b) tonic activity during waking a nd rapid-eye-movement sleep. Spindle waves are generated largely throu gh a cyclical interaction between thalamocortical and thalamic reticul ar neurons involving both the intrinsic membrane properties of these c ells and their anatomical interconnections. Specific alterations in th e interactions between these cells can result in the generation of par oxysmal events resembling absence seizures in children. The release of several different neurotransmitters from the brain stem, hypothalamus , basal forebrain, and cerebral cortex results in a depolarization of thalamocortical and thalamic reticular neurons and an enhanced excitab ility in many cortical pyramidal cells, thereby suppressing the genera tion of sleep rhythms and promoting a state that is conducive to senso ry processing and cognition.