EEG changes induced by light stimuli modulated with the subjects alpha rhythm.

A new method, named the 'alpha wave modulated light' (AML) stimulation, has been used for controlling the frequency of sine wave modulated light by the subject's on-going alpha rhythm. The EEG was recorded from O1 and O2. With the AML stimulation using either the left occipital alpha rhythm or the right, two phase differences of O degrees and 180 degrees were created between AML and the alpha rhythmn. The peak frequency and power of occipital alpha in both hemispheres and the coherence and phase between the left and right occipital EEG were obtaned for 7 subjects. The alpha power was larger at a 180 degrees phase shift than at a 0 degrees phase shift with ipsilateral AML stimulation. The ipsilateral increase in the alpha power was greater than the contralateral at a 180 degrees phase shift. Larger coherence value and right phase lead were observed at 180 degrees phase shift by use of the right alpha rhythm. The possible mechanisms of influences of AML stimulation on the alpha activity were discussed.