Stochastic resonance in brain activity elicited by auditory stimuli

We measured auditory steady state responses (ASSRs) in magnetoencephalogram to an ongoing sinusoidal amplitude modulated tone presented to the subject's left ear while bursts of white noise of various intensities were presented to the right ear. Because the power and coherence as functions of the noise to signal ratio differed considerably among subjects, we used their maximum values as test statistics for testing the group data. The results showed a significant enhancement in the phase coherence of ASSRs obtained over the right temporal regions by the presence of white noise of appropriate intensity. The observed stochastic resonance (SR) most likely occurred within the central nervous system. Our finding may be quite important as mechanisms of SR in biological systems are mostly unknown.