Obligatory Broca's area modulation associated with passive speech perception.

Broca's area is crucial for speech production. Several recent studies have suggested that it has an additional role in visual speech perception. This conclusion remains tenuous, as earlier studies used tasks requiring active processing of visual speech movements, which may have elicited conscious subvocalizations. To study whether Broca's area is modulated during passive viewing of speech movements, we conducted a functional MRI experiment where participants detected rare and brief visual targets that were briefly superimposed on two task irrelevant conditions: passive viewing of silent speech versus nonspeech (gurning) facial movements. Comparison revealed Broca's area to be more active when observing speech. These findings provide further support for Broca's area in speech perception and have clear implications for rehabilitation of aphasia.