Hemispheric asymmetry in N100m current sources in auditory evoked fields: Comparison of ipsilateral versus contralateral responses

We analyzed auditory evoked magnetic fields to 400 Hz tone bursts presented at right or left ear to investigate whether a hemispheric asymmetry exists. The mean onset and peak latencies of N100m response are longer in the ipsilateral hemisphere to the stimulation site than in the contralateral hemisphere; however, the latencies of the ipsilateral N100m in right hemisphere (RH) were shorter than those in left hemisphere (LH). As to dipole strength, a right-ward asymmetry was found for left ear stimulation but the dipole strength was symmetrical between RH and LH for right ear stimulation. The current sources in contralateral and ipsilateral N100m responses moved toward anterolateral direction along the long axis of the Heschl gyrus before the peak latency; in general, the ipsilateral response was located slightly posterior to that for the contralateral one. The traveling distance of the current sources in RH for right ear stimulation was longer than that in LH for left ear stimulation. These results suggest the right-dominant hemispheric asymmetry in pure tone processing.