Dissociation between Olfactory and Auditory-Verbal Processing in the Occipital Cortex of Early Blind Subjects

Despite numerous studies on cross-modal brain plasticity, it is still unclear to what extent distinct (nonvisual) sensory modalities are segregated in the reorganized occipital cortex (OC) of blind subjects. In addition, little is known about the potential role of the OC in olfactory processing that is enhanced in these subjects. Using fMRI, we monitored the brain activity in ten early blind (EB) subjects while they were discriminating or categorizing olfactory (fruit and flower odors) versus auditory-verbal stimuli (fruit and flower names). Both modalities selectively activated the ventral part of the OC and were segregated in this cortex; the right fusiform gyrus was most activated during olfactory conditions while part of the left ventral lateral occipital complex showed a preference for auditory-verbal processing. No such occipital activation was observed in sighted controls, but the same right-olfactory/left-auditory hemispheric lateralization was found overall in their brain. These findings constitute the first evidences (1) that the OC is involved in the processing of odors in EB subjects and (2) that sensory modalities are (to some extent) segregated in the OC of EB subjects. Furthermore, the ventral stream seems to develop its designated functional role in processing stimulus identity independently of visual experience