Stabilization of alpha frequency by sinusoidally modulated light.

Two experiments demonstrate that a spontaneous electroencephalographic (EEG) rhythm, alpha, can be frequency-stabilized by sinusoidally modulated light (SML) but not by photic flash stimulation. It is suggested that this frequency stabilizing effect is not due to superimposition of an evoked response on the background EEG. Instead, SML might phase-lock the scalp-recorded alpha rhythm by influencing subcortical alpha generators within narrow limits set by the inherent resonant EEG frequency.