Magnetoencephalographic study of human auditory steady-state responses to binaural beat

Abstract Presentation of one sinusoid to each ear with a small difference of frequency elicits subjective fluctuations called binaural beat (BB). BB is a classic example of binaural interaction and provides a typical demonstration that the discharges of the auditory nerve fibers preserve information on the phase of the acoustic stimuli. Neural spikes tend to occur at a particular phase of the sinusoidal waveform (phase locking). The central auditory system utilizes the information of interaural phase difference (IPD) with continuous and periodical oscillation. The apparent beat frequency heard is equal to the IPD provided. In order to confirm the cortical representation of fluctuation of BB, we recorded the magnetic field of the auditory steady-state response (SSR) evoked by BBs in six normal-hearing right-handed subjects. Periodical responses with small amplitude were recorded around the bilateral temporal areas by a wholescalp neuromagnetometer under presentation of slow BB (4 and 6.66 Hz). Spectral analysis detected peaks of the BB frequency in the channels of bilateral temporal areas. These results suggested that activity of cerebral cortex, especially auditory cortex, can be synchronized with slow BB and have capacity for preserving the information of IPD.