The influence of the level of prestimulus alpha
phase synchronicity on the N100 component and reaction
time (RT) was examined, in target auditory oddball data
from 25 normal subjects. Alpha phase synchronicity is a
new measure consisting (for a given stimulus presentation)
of the angular or circular variance of the alpha phase
at stimulus onset across the parieto-occipital sites. The
lower the angular variance, the higher the phase synchronicity
(the more closely in phase the alpha activity across these
sites) and vice versa. Subaveraged event-related potentials
(ERPs) were formed for high and low prestimulus alpha phase
synchronicity stimulus presentations. N100 amplitude was
significantly greater in the high than the low phase synchronicity
subaverages. In addition, RT was significantly reduced
in the high prestimulus alpha phase synchronicity cases.
Alpha phase synchronicity reflects an aspect of brain state
that influences subsequent stimulus processing.