Nature of crossmodal plasticity in the blind brain and interplay with sight restoration

The present Ph.D. work was dedicated to the study of experience-dependent brain plasticity associated with visual deprivation/restoration. In two cross-sectional studies involving the use of functional magnetic resonance imaging in a group of participants with congenital or early blindness (and in a control group of sighted participants), we attempted to characterize the way the occipital cortex - typically devoted to vision – reorganizes in order to process different auditory stimuli. We demonstrate that in case of early visual deprivation, distinct regions of the occipital cortex display a functional preference for specific non-visual attributes, maintaining a functional specialization similar to the one that characterizes the sighted brain. Such studies have shed new light on the role played by intrinsic constraints on the one side, and experience on the other, in shaping the modality- and functional tuning of the occipital cortex. On the one hand, the observation of occipital responses to auditory stimulation (crossmodal plasticity) highlights the ability of the occipital cortex to reorient its preferential tuning towards the preserved sensory modalities as a function of experience. On the other hand, the observation of specialized cognitive modules in the occipital cortex, similar to those observed in the sighted, highlights the intrinsic constraints imposed to such plasticity. In a longitudinal single-case study, we further explored how the neuroplastic changes associated with blindness may interact with the newly reacquired visual inputs following partial visual restoration in adulthood. We performed both pre- and post-surgery measurements in a sight-recovery patient combining behavioral, neurostructural and neurofunctional methods in order to jointly investigate the evolution of crossmodal reorganization and visual recovery across time. We demonstrate that functional and structural changes evidenced in the visually-deprived occipital cortex can only partially reverse following sight restoration in adulthood. Altogether, our findings demonstrate the striking adaptability of the occipital cortex facing drastic changes in visual experience.