Final Report Summary - MADVIS (Mapping the Deprived Visual System: Cracking function for prediction) One of the most striking demonstrations of experience-dependent plasticity comes from studies of blind individuals showing that the occipital cortex (traditionally considered as purely visual) massively changes its functional tuning to support the processing of non-visual inputs. These mechanisms of crossmodal plasticity, classically considered compensatory, inevitably raise crucial challenges for sight- restoration. How will the non-visual inputs interfere, coexist or disappear following the re-acquisition of vision? Addressing this issue is particularly timely now, given the recent advent of sight-restoration techniques. The neglected relation between crossmodal plasticity and sight-recovery represents the testing ground for MADVIS in order to gain important novel insights on how specific brain regions become, stay and change their functional tuning towards processing specific stimuli. MADVIS made significant breakthroughs on two fronts: (1) understanding how visual deprivation at different sensitive periods in development affects the functional organization and connectivity of the occipital cortex; and (2) using the fundamental knowledge derived from (1) to test and predict the outcome of sight restoration. We were able to show that the recruitment of occipital (visual) regions by non-visual inputs in blind individuals highlights the ability of the brain to remodel itself on the basis of experience (nurture influence). However, the observation that the (re)organized occipital cortex of the blind for sound processing shares similar representational structure as the one observed in the sighted for vision highlights the intrinsic constraints imposed on such plasticity (nature influence). Using a series of connectivity tools, MADVIS was able to support the idea that the expression of brain reorganization in blind people is guided by a potentially innate pattern of connectivity between occipital regions and the rest of the brain. Such pattern of connectivity scaffolds the expression of plastic changes in the blind and help maintaining the functional homeostasis of brain regions for a specific function.Then, MADVIS had for objective to relate the knowledge gathered from blind people to sight-restoration. We have been able to demonstrate that visual deprivation, if appearing early in life, leads to long-lasting changes in occipital regions for the processing of visual and auditory information that remains for years after sight-recovery. Somehow surprisingly, these brain and behavioral reorganizations can also be found if the period of deprivation is very short (e.g. few months) but early in life. We believe that the methodological and conceptual developments that have been at the core of the MADVIS project have profound impacts far beyond the scope of our project by allowing neuroscientist to better understand how our sensory experience drives the functional development of brain regions.
