Spontaneous and evoked EEG-activity during one-second light-stimulation (author's transl)]

EEG data were recorded in 13 students during one-second light-stimulation with eyes closed and sometimes eyes opened, from central and occipital regions. The background EEG was computer-analyzed in the alpha-band using the power time course where a short decrease in power was indicative of a phasic desynchronization of the rhythmic activity within the alpha-band. The maximal desynchronization was observed in the occipital region independent of eyes-opened or eyes-closed conditions. With eyes closed a reinforced power decrease was found 0.25-0.5 sec after the on- and offset of light-stimulation, which was interpreted as "on"- and "off"- effect of the background EEG activity. Parallel with the on- and off-effect a slow potential change occurred in the evoked responses. The behaviour of the background activity during 1 sec light-stimulation was intramodality specific in contrast to the evoked response which showed an intramodality unspecific behaviour with maximal amplitude in the central region.