Convergence of finger tremor and EEG rhythm at the alpha frequency induced by rhythmical photic stimulation.

The frequencies of EEG alpha rhythm and physiological finger tremor overlap at 9-10 c/sec, suggesting a functional relationship between the two mechanisms. We measured the correlation between the two rhythms when they occurred spontaneously and when rhythmical photic stimulation was applied. Rhythmical physiological finger tremor (9.7 c/sec +/- 1.06 S.D.) was accompanied by an alpha rhythm (10.3 c/sec +/- 0.51 S.D.) spontaneously, showing a one-to-one relationship at times. When photic stimulation was provided at a frequency (11 Hz) close to the subject's spontaneous alpha rhythm, a frequency-convergence occurred between finger tremor (10.3 c/sec +/- 0.68 S.D.) and the EEG (10.6 c/sec +/- 0.35 S.D.). The correlation coefficient between the two rhythms under photic stimulation was significantly higher (0.49 +/- 0.14 S.D.) than under the spontaneous condition (0.13 +/- 0.16; P less than 0.05). Consistent with this, the mean difference between finger tremor and EEG frequencies was significantly lower during photic stimulation (0.83 c/sec +/- 0.46 S.D.) than during the spontaneous condition (1.23 c/sec +/- 0.82 S.D.) (t = 2.54; P less than 0.05, t-test for correlated means). These findings indicate that the EEG and physiological finger tremor tend toward synchrony with each other in an environment of photic stimulation, supporting our hypothesis of a functional relationship between the two mechanisms.