Alpha wave phase and alpha attenuation

Abstract

1. 1. Previous reports indicated that phase of the occipital alpha wave and cortical excitability are related. Habituation of the alpha attenuation response (AAR) to both visual and auditory stimuli was examined with a view to determining whether different degrees of habituation would be demonstrated when stimuli are presented at different phases of the alpha wave. In addition, contingent alpha attenuation in a paired click-flash sequence was examined. 2. 2. Subjects with abundant, fairly high amplitude alpha activity were assigned randomly to one of five groups determined by the point on the alpha wave at which they were stimulated. The groups were further divided into four subgroups, each of which had the procedure repeated with stimuli presented at one of the other points on the alpha wave. Stimuli were delivered by an automatic alpha recognition device using zero crossing detection. Forty presentations of single and paired stimuli were presented during runs of alpha activity with at least 5 sec and one unstimulated train of alpha waves between successive stimuli. 3. 3. The duration of the AAR decreased with successive blocks of trials to the least extent and most slowly for subjects stimulated randomly. Duration decreased most rapidly for the group stimulated at the peak of alpha wave with clicks and for the group stimulated midway on the up-going portion of the wave with flashes. In the paired condition, there was a tendency for those subjects stimulated at the trough of the wave to reach criterion in the fewest number of trials. 4. 4. The results of the present study suggest that phase of the alpha wave is associated with cortical excitability. When phase is corrected for conduction time, most rapid habituation to the flash and click stimuli occurs when the alpha cycle is moving toward surface positivity. However, the trend toward most rapid contingent AAR occurs when the contingent stimulus is presented as the alpha phase is moving toward surface negativity.