The phase of postural hand tremor is not influenced by repetitive photic brain stimulation

Powerful photic stimulation was employed to produce driving of the EEG rhythm recorded from occipital cortex. The resulting quasi-sinusoidal signal was considerably larger than the spontaneous alpha rhythm, and Fourier analysis showed it to be sharply tuned to the frequency of the stimulation which ranged from 7–11 Hz. Physiological postural hand tremor was recorded bilaterally during the period of stimulation. Signal averaging was used to investigate the relationship of the EEG and tremor waveform to the light flashes. The EEG was clearly phasically related to the repetitive stimulus, but the waveform of the tremor was not. We conclude that this external stimulus fails to produce a detectable entrainment of motor output.