Auditory response following vocalization: a magnetoencephalographic study

Objective: We recorded vocalization-related cortical fields (VRCF) under co mplete masking of a subject's own voice to identify the auditory component evoked by a subject's own voice in the VRCF complex. Methods: We recorded VRCF during simple vowel (/u/) vocalization in 10 righ t-handed healthy volunteers under two conditions: (1) no masking (control) and (2) masking of the subject's own voice by weighted-white noise during v ocalization. In the second experiment, we recorded auditory evoked magnetic fields (AEF) following stimulation of a speech sound applied by voice-reco rder. Results: The onset of VRCF appeared gradually before the vocalization onset , and a clear phase-reversed deflection was identified after the onset of v ocalization. The difference waveform obtained by subtracting the VRCF of th e masking condition from that of the control showed a deflection (1M) at 81 .3 +/- 20.5 (mean +/- SD) ms after the onset of vocalization, but then was no consistent deflection before the vocalization onset. The AEF following v oice sound in the second experiment showed the M100 component at 94.3 +/- 1 8.4 ms. The equivalent current dipole of the 1M component for different wav eforms was located close in the auditory cortex to that of the M100 for AEF waveforms in each hemisphere. Conclusion: We successfully separated the auditory feedback response from t he VRCF complex, using an adequate masking condition during vocalization of a subject's own voice. The masking effect was crucial to the auditory feed back process after the onset of vocalization. The present results suggested that the 1M component was mainly generated from the auditory feedback proc ess by the subject's own voice. The activated auditory area for simple own voice might be similar to that for simple external sound. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.