The Motor Somatotopy of Speech Perception

Listening to speech recruits a network of fronto-temporoparietal cortical areas [1]. Classical models consider anterior (motor) sites to be Involved In speech production whereas posterior sites are considered to be Involved In comprehension [2]. This functional segregation Is challenged by action-perception theories suggesting that brain circuits for speech articulation and speech perception are functionally dependent [3, 4]. Although recent data show that speech listening elicits motor activities analogous to production [5-9], It's still debated whether motor circuits play a causal contribution to the perception of speech [10]. Here we administered transcranial magnetic stimulation (TMS) to motor cortex controlling lips and tongue during the discrimination of lip- and tongue-articulated phonemes. We found a neurofunctional double dissociation In speech sound discrimination, supporting the Idea that motor structures provide a specific functional contribution to the perception of speech sounds. Moreover, our findings show a fine-grained motor somatotopy for speech comprehension. We discuss our results In light of a modified motor theory of speech perception according to which speech comprehension Is grounded In motor circuits not exclusively Involved In speech production [8].