Brain stimulation during sleep

This article discusses cortical polarization and induction of brain rhythms during sleep via brain electric and magnetic stimulations and resultant functional changes. The studies presented here underscore the strong dependence on the ongoing brain activity of the induced effects on electroencephalogram (EEG) and behavioral measures. The reviewed data on the effect of applied electric currents on brain electric activity and behavior boost the reemerging concept that endogenous oscillating fields are per se of physiologic and functional significance. Applying weak electric currents is a promising approach for investigating different cortical EEG rhythms and their immediate interactions and functional implications for behavior.