[Basic mechanism for generation of brain rhythms].

Study of the basic mechanism of brain rhythms adds to our understanding of the underlying processes of neuronal network within the human brain. Electroencephalography (EEG) records summated extracellular field potentials from large pyramidal neurons in the cerebral cortex. The characteristic rhythmic oscillation of brain rhythms are beststudied by sleep spindles, which are generated within the thalamus through a network of thalamic reticular cells, thalamocortical projection cells and cortical pyramidal cells. Fast rhythms including beta and gammaare present during arousal and focused attention. Besides a reflection of activation from the brainstem reticular activating system, fast rhythms also represent an activated state of the underlying neuronal network. Alpha waves are readily recognized brain waves during relaxed wakefulness; however, the origins of alpha rhythm are not well understood. It is presumed that alpha rhythms are generated by contingent pyramidal cell, and by intracortical connections, spread in the cortical layers. Rhythmic alpha spindles probably represent a de-activated state.