Broca's area in language, action, and music.

The work of Paul Broca has been of pivotal importance in the localization of some higher cognitive brain functions. He first reported that lesions to the caudal part of the inferior frontal gyrus were associated with expressive deficits. Although most of his claims are still true today, the emergence of novel techniques as well as the use of comparative analyses prompts modern research for a revision of the role played by Broca's area. Here we review current research showing that the inferior frontal gyrus and the ventral premotor cortex are activated for tasks other than language production. Specifically, a growing number of studies report the involvement of these two regions in language comprehension, action execution and observation, and music execution and listening. Recently, the critical involvement of the same areas in representing abstract hierarchical structures has also been demonstrated. Indeed, language, action, and music share a common syntactic-like structure. We propose that these areas are tuned to detect and represent complex hierarchical dependencies, regardless of modality and use. We speculate that this capacity evolved from motor and premotor functions associated with action execution and understanding, such as those characterizing the mirror-neuron system.