The effects of rhythmic or random photic and sonic stimulations upon the called minor tremors (MT) on the human body surface were studied. MT was traced by an electroencephalograph simultaneously with the recording of electroencephalogram (EEG) and heart beat or electrocardiogram (EKG). In addition to simple visual inspection of the tracings, the average time-and frequency-patterns were obtained for some cases by auto-and crosscorrelogram and power spectra analysis respectively.
The study of the MT tracing and crosscorrelogram between the stimulation and MT showed that MT components which synchronize with the frequency of the stimulation were driven by rhythmic flash stimulation. In addition, increased regularity and rhythmicity of MT were found in the autocorrelogram of MT, even when the driven component of MT produced by stimulation is not so evident on visual inspection. On the other hand, it was shown in the autocorrelogram that the damping of oscillation becomes faster by random flash stimulation. The same phenomena as those produced by photic stimulation were also demonstrated with rhythmic and random sonic stimulations, though is not so clear as those in rhythmic and random flash stimulations.
From the above results, it seems likely that the central process of the neuromuscular system such as augmentation and inhibition might be represented respectively by the increase and decrease of driven MT during various sensory stimulations, though ballistcardiographic oscillations are mixed in MT.