VISUAL AND AUDITORY-EVOKED PHASE RESETTING OF THE ALPHA-EEG

An increasing number of studies over the last decade or so have sugges ted that evoked potential (EP) morphology is partially due to a reorga nization of the phase of the ongoing EEG. Phase resetting is common to non-linear oscillatory systems in response to a perturbation and has been observed in a number of biological systems such as circadian rhyt hms and the EGG. However, it has not been studied adequately in the co ntext of EP research. Five clinically normal male volunteers (age 25-3 2) were subjected to randomly occurring light flashes for approximatel y 1 h. EEG recordings were obtained from a midline parieto-occipital s ite (POz) referenced to linked ears. An additional five male subjects (age 26-36) participated in an auditory P3 study of the effects of nim odipine, a calcium channel blocker, on brain electrical activity. Four of the latter subjects were diagnosed as crack cocaine abusers and on e was negative for crack use. The single trials were bandpass filtered in the 8-13 Hz band and the phase angle at the moment of stimulation was computed. We examined the relationship between initial phase angle and both latency and amplitude of the first two post-stimulus negativ e peaks. The results demonstrate that these peaks undergo phase and (p re-stimulus) amplitude sensitive latency reorganization during present ation of both visual flash stimuli and auditory non-target oddball sti muli in a P3 experiment. (C) 1997 Elsevier Science B.V.