Article: PDF OnlyNovak Peter; Lepicovska, VeraNeuroReport: February 1992 - p 189-192 Buy Abstract TIME variation of the successive 2.5 s long EEG theta and alpha band powers during 5 min rest and 4 min hyperventifation (HV) was analyzed by modified Wigner distribution (WD) in 22 subjects. Two main peaks at frequency 0.02 Hz and 0.068 Hz were detected in the WDs of both alpha and theta powers at rest. The HV increased the magnitude of the faster (0.068 Hz) component of both theta and alpha WD's while the slower (0.02 Hz) component was increased only in the theta WD. We hypothesize that this slow brain activity reflects spontaneous periodic changes of cortical excitability with control at the brain stem level. © Lippincott-Raven Publishers.