Abstract
We experimentally study stochastic resonance (SR) in the human brain through a noise effect for entrainment dynamics of the alpha (α) wave. The measurement has been carried out under the following conditions in order to obtain clear evidence of the SR phenomenon in the central nervous system. The periodic and noisy stimuli are respectively applied to the right and the left eyes of the subject independently. When only periodic and constant (but weak enough) stimulus is applied to the right eye, it does not induce any global entrainment of α-oscillators to the stimulus frequency. In this situation increasing the amplitude of the noise stimulus (frequency bandwidth from 15 to 60 Hz), harmonic entrainment occurs for a certain range of the noise amplitude and shows a sharp peak in the power spectrum of brain waves. Plotting the amplitude of the peak against the noise amplitude, a bell-type shape is seen, i.e. the maximum signal amplitude at an optimum noise. It clearly indicates the SR phenomenon. Taking account of our experimental conditions and set-up, the present SR phenomenon occurs not on the retina but on the visual processing area in the central nervous systems beyond the optic chiasma.
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