Some characteristics of stimulus-provoked alpha activity

Abstract

Two groups of subjects, pre-selected for prominent resting alpha, were studied in order to assess the habituation of EEG reactivity to repeated photic stimuli. In one group, the subjects passively received the signals; in the other they were instructed to respond manually as soon as the signal was detected, and the reaction times were measured. It was found that the EEG background of alpha activity tended to alternate with a lower voltage, more random pattern sometimes including slow waves in both groups. The EEG reactivity against the latter background was that of provocation of alpha activity, whereas against the background alpha rhythm, the reactivity was that of blocking or arrest of alpha. From the point in each record in which these patterns began to alternate, it was found that the alpha provocation response had a higher incidence than the desynchronization response, significantly so only for the group not required to respond. The blocking response was relatively habituated for both groups. The requirement of a motor response to the photic signal was associated with an increased incidence of the alpha blocking response. Reaction times tended to be higher when alpha provocation occurred. The hypothesis was advanced that stimulation-provoked alpha activity may be an electrical sign of central inhibitory processes.