Brain areas commonly activated and asymmetrical in production, listening and reading tasks at the word level: an fMRI study of 144 right-handers.

Neuroimaging studies on language have revealed that the conjunction between speech production and comprehension elicited a common implication of frontal and temporal regions and it is now admitted that speech perception and production rely on both auditory and motor areas. This overlap has been revealed to be also present between reading and listening, but so far no study has simultaneously investigated the overlap of regions involved in the three language tasks (production, perception and reading). The aim of this study is to identify leftward heteromodal brain areas common to these 3 language tasks and to question the existence of right brain areas. Using functional MRI and a new functional regional atlas totally suited for investigating brain lateralization, we performed a conjunction of activated and asymmetrical brain areas in 144 right-handers, to determine the core language areas involved in word list production, perception and reading. Results revealed 3 leftward-clusters, the first one included areas along the central sulcus and premotor supplementary area, the second one included hand motor area, the third one included two regions of the supramarginal gyrus. One the right, the first cluster out of 3 was made of the superior temporal sulcus (STS3). Leftward frontal and precentral areas together with temporo-parietal areas have been revealed to be commonly activated and asymmetrical, leading to the hypothesis of the involvement of phonological action perception circuits such as the phonological working memory loop, in which articulatory gestures are the central motor units on which word perception, production and reading would develop and act according to the motor theory of speech. On the right hemisphere, the common activation and asymmetry of the STS3, which is a prosodic integrative area, could reflect the processing of fine spectral details over time.

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