Broca's area is crucial for visual discrimination of speech but not nonspeech oral movements

Abstract

Broca’s area (BA) is crucial for normal speech production, but its role in speech comprehension remains controversial. We used repetitive Transcranial Magnetic Stimulation (rTMS) to reveal that briefly disrupting BA impairs discrimination of visual speech oral movements, but not visual non-speech oral movements. This provides direct evidence that BA is useful in the perception of visual speech information. We demonstrate that the region of the brain responsible for producing speech has a role in the visual perception of speech information, and importantly is not involved in the visual perception of oral movements (gurning) unrelated to speech. Because disrupted performance was observed for speech movements and not nonspeech movements, our data suggests that this form of perception does not benefit from an amodal mirror neuron system general enough to be recruited in the processing of common mouth movements irrespective of their relation to speech. We propose that BA is recruited in the perception of speech because of its role in producing speech.