Dynamic anterolateral movement of N100m dipoles in evoked magnetic field reflects activation of isofrequency bands through horizontal fibers in human auditory cortex

Abstract

To analyze the temporal changes in localization of an equivalent current dipole (ECD) for the auditory N100m, we recorded auditory evoked magnetic fields (AEFs) to 400 Hz tone pips presented at the right or left ear. Using a single ECD model, the dipole location for the N100m sources was successively calculated from the AEFs obtained from the hemisphere contralateral to the stimulated ear. We found that the location of the N100m current sources moved dynamically in medio-lateral and postero-anterior directions before the N100m peak. This direction was parallel to the surface of the supratemporal cortex. We propose that the dynamic movement of the N100m dipole reflects spread of intracortical activation through horizontal fibers of pyramidal neurons in the auditory cortex, forming the isofrequency bands in humans.