Spatiotemporal source analysis of vocalization-associated magnetic fields.

The vocalization-related cortical fields (VRCF) following vowel vocalization were studied by magnetoencephalography (MEG) in eight normal subjects. A multiple-source model, BESA (Brain Electric Source Analysis), was applied to elucidate the generating mechanism of VRCF in the period from 150 ms before to 150 ms after the onset of vocalization. Six sources provided satisfactory solutions for VRCF activities during that period. Sources 1 and 2, which were activated from approximately 150 ms before the vocalization onset, were located in laryngeal motor areas of the left and right hemispheres, respectively. Sources 5 and 6 were located in the truncal motor area in each hemisphere, and they were very similar to sources 1 and 2 in terms of temporal change of activities. Sources 3 and 4 were located in the auditory cortices of the left and right hemispheres, respectively, and they appeared to be activated just after the vocalization onset. However, all six sources were temporally overlapped in the period approximately 0-100 ms after the vocalization onset. The present results suggested that the bilateral motor cortices, probably laryngeal and truncal areas, were activated just before the vocalization. We considered that the activities of the bilateral auditory areas after the vocalization were the response of the subject's central auditory system to his/her own voice. The motor and auditory activities were temporally overlapped, and BESA was very useful to separate the activities of each source.