Subject's own speech reduces reactivity of the human auditory cortex

Previous studies on monkeys have shown that uttering-related cortical areas exert an inhibitory effect on the auditory cortex, and cerebral blood-flow analyses on humans have revealed modulation of the activity of the auditory cortex during own speech. To study this modulation on a millisecond time scale, we recorded neuromagnetic evoked responses to short 1-kHz tones while the subjects were reading silently and aloud. The 100-ms response (M100) of the auditory cortex was delayed by 10-21 ms and its amplitude was dampened by 44-71% during reading aloud compared with reading silently. This effect was more prominent in responses to ipsilateral than contralateral tones, possibly due to a sum effect of diminished ipsilateral input to the cortex and decreased transcallosal excitation.