Sensorimotor activation related to speaker vs. listener role during natural conversation

Although the main function of speech is communication, the brain bases of speaking and listening are typically studied in single subjects, leaving unsettled how brain function supports interactive vocal exchange. Here we used whole-scalp magnetoencephalography (MEG) to monitor modulation of sensorimotor brain rhythms related to the speaker vs. listener roles during natural conversation. Nine dyads of healthy adults were recruited. The partners of a dyad were engaged in live conversations via an audio link while their brain activity was measured simultaneously in two separate MEG laboratories. The levels of ∼10-Hz and ∼20-Hz rolandic oscillations depended on the speaker vs. listener role. In the left rolandic cortex, these oscillations were consistently (by ∼20%) weaker during speaking than listening. At the turn changes in conversation, the level of the ∼10Hz oscillations enhanced transiently around 1.0 or 2.3s before the end of the partner's turn. Our findings indicate left-hemisphere-dominant involvement of the sensorimotor cortex during own speech in natural conversation. The ∼10-Hz modulations could be related to preparation for starting one's own turn, already before the partner's turn has finished.