Phase of alpha brain waves, reaction time and visually evoked potentials

Abstract

A reaction time study was conducted in which twenty subjects were asked to respond to single flashes of light by closing a response switch as quickly as possible. The flashes were presented during six different phase intervals of alpha waves to determine whether reaction times would be related to alpha phase, thus reflecting changes in cortical excitability. Reaction times were found to be reliably faster when the stimulus light was flashed during certain portions of the alpha wave, thus supporting the hypothesis of an excitability cycle being related to the alpha wave. Inked plots of the resulting averaged visually evoked potentials yielded a complex wave consisting of eight distinct components in the first 300 msec of the response. Only two of these components correlated positively and significantly with reaction time. The peak delay of the earliest and most highly correlated of the two components was used as a measure for the interval of time required for the volley initiated by the flash to have reached the cortex and the neural integration necessary for “perception” to have occurred. When the alpha phase during which the light was flashed was corrected by this amount (57 msec), fastest mean reaction times were found to fall on a surface negative phase of the wave while the slowest fell on a positive phase.