Stochastic Resonance in Evoked Magnetoencephalogram Investigated by Analysis of Coherences

We examined the phase coherence and power of auditory steady state responses (ASSRs) in magnetoencephalogram to an ongoing sinusoially amplitude modulated tone presented to the subject's one ear while bursts of white noise of various intensities were presented to the opposite ear. We also examined the real and imaginary parts of coherence between the ASSRs of the right and left auditory temporal regions. Stochastic resonance (SR) was seen in the phase coherence and power of the ASSR from the contralateral temporal area and in the real part of the right-left coherence. The results showed that the SR phenomenon occurred not in the periphery but in the central nervous system and suggested that it was not probably due to the interaction between the left and right auditory cortex.