Effect of early visual deprivation on perception and semantic processing of odors

(eng) A large number of studies provided evidences of enhanced tactile and auditory performances in early blind (EB) individuals as compared to sighted control (SC) subjects. The emergence of these behavioral adjustments in early blindness has been usually associated with a functional reorganization of the brain, in particular in the occipital cortex, a region traditionally considered as supporting visual functions in sighted subjects. It is thought that the cross-modal recruitment of deafferented “visual” brain areas facilitate the emergence of practice-related behavioral adjustments in blind subjects to process non-visual information. While the auditory and tactile modalities and related higher cognitive functions have been thoroughly investigated in blind subjects, the current knowledge about olfactory perception in this population is clearly minor. The present PhD thesis provides new insights into the sensory and cognitive functions in EB people, bringing original data about the perception and semantic processing of odors. It includes both behavioral studies using several psychophysical tests of olfactory abilities (chapter II) and functional neuroimaging investigations of olfactory perception using neurophysiological and brain imaging techniques (chapter III). Results indicate that EB subjects develop compensatory mechanisms in the olfactory domain at a sensory level (i.e. odor detection) and basic level of perception (i.e. odor discrimination) as well as in higher-order levels of olfactory processing (i.e. free-identification of odors and odor categorization). Although passive olfactory and trigeminal stimulation (i.e. without task) does not reveal significant differences between EB and SC subjects, EB subjects activate significantly their occipital cortex compared to blindfolded controls during tasks that require low level perceptual processing and higher level semantic processing of odors (i.e. odor discrimination and categorization, respectively). This leads us to conclude that behavioral adjustments of early blind subjects through non-visual sensory modalities also apply to olfaction. While additional studies are clearly needed, the present results indicate that early blind subjects could make a larger use of odorous stimuli than sighted individuals to compensate for the lack of vision. In addition, the occipital cortex of EB subjects is involved in perceptual and high-level cognitive processing of odors. The cross-modal recruitment of the occipital cortex might be considered as a factor influencing olfactory perceptual skills in this population. Moreover, the observation of cross-modal reorganization in the occipital cortex of EB subjects to process olfactory information might be considered as a further and highly original evidence for the multimodal and supra-modal character of the occipital cortex when early deprived of visual input.