Compensatory cross-modal plasticity of speech perception and production neural networks in congenitally blind adults
Résumé
Visual cues play an important role in the development of speech perception and production. Deprived of the visual correlates of articulatory gestures, congenitally blind speakers rely only on the auditory and somatosensory modalities to perceive and produce speech. In order to test whether visual brain areas might be recruited in a compensatory cross-modal manner during speech perception and production, we here focus on the neural substrates of vowel perception and production in both congenitally blind and sighed adults. In order to minimize scanner noise and movement-related imaging artifacts, a sparse sampling acquisition technique was used where participants produced or passively listened to a vowel during a silent interval between successive image acquisitions. For vowel perception, a conjunction analysis revealed common bilateral activations for both groups in the superior temporal gyrus/sulcus extending to the ventral part of the inferior parietal cortex. In addition, a group comparison showed specific bilateral activations in the calcarine gyrus and the superior/middle occipital gyri for blind participants. For vowel production, the conjunction analysis revealed a bilateral set of brain areas classically involved in motor control: the sensorimotor cortex, the premotor cortex, the inferior frontal gyrus, the supplementary motor area and the anterior cingulate gyrus, the superior and inferior parietal lobules, the insula, the basal ganglia, the thalamus and the cerebellum. The group comparison further showed specific reduced neural responses for blind participants in the prefrontal cortex, the right superior parietal gyrus, the basal ganglia, the cerebellum and the posterior cingulate gyrus. Interestingly, no activations were observed in the visual cortex during the production task. Compared to vowel perception, reduced activity observed for both groups in the auditory cortex as well as in the visual cortex for blind participants might reflect motor-to-sensory feedback control mechanisms. Altogether, these results provide clear evidence for cross-modal plasticity due to early visual deprivation of the neural networks involved in speech perception and production.