Renier, L. & De Volder, A. G.
Institute of Neuroscience, Neural Rehabilitation group, Université catholique de Louvain, Brussels, Belgium
It is now established that the elevated metabolism in the deafferented “visual” cortex of congenitally blind adults has a physiological significance. Despite numerous studies on cross-modal brain plasticity, still little is known about how their “visual” cortex is functionally organized. On the one hand, several occipital regions in blind subjects seem quite indifferently recruited in various experimental conditions (tasks and stimuli), which led some authors to propose that this activation is nonspecific and serves a general purpose. On the other hand, numerous studies brought evidences of the existence of functional specializations in the occipital cortex of blind subjects. Using functional brain imaging (PET and fMRI) we monitored the brain activity in early blind and sighted control subjects while they were involved in various tasks including spatial imagery, mental imagery of object shape, auditory motion processing, localization of auditory and vibrotactile stimuli as well as during the use of a visual-to-auditory sensory substitution device to perceive 2D geometrical figures, schematized faces and houses. In total we brought evidences in favour of a preserved functional specialization within the ventral and dorsal “visual” streams in early blind subjects. In addition we recently observed that the occipital cortex was involved in the processing of odours in early blind subjects and that olfactory and auditory-verbal processing was segregated in their reorganized cortex. This leads us to conclude that there is a functional specialization in the occipital cortex of early blind subjects: sensory modalities are to some extent segregated in this reorganized cortex and the “visual” streams seem to develop their designated functional role in processing spatial and nonspatial stimuli regardless of visual experience