Right Occipital Cortex Activation Correlates with Superior Odor Processing Performance in the Early Blind

Laurent Renier,Isabel Cuevas,Cécile B Grandin,Laurence Dricot,Philippe Rombaux,Elodie Lerens,Anne G De Volder,Paula Plaza,Maurice Ptito

doi:10.1371/journal.pone.0071907

Abstract

Using functional magnetic resonance imaging (fMRI) in ten early blind humans, we found robust occipital activation during two odor-processing tasks (discrimination or categorization of fruit and flower odors), as well as during control auditory-verbal conditions (discrimination or categorization of fruit and flower names). We also found evidence for reorganization and specialization of the ventral part of the occipital cortex, with dissociation according to stimulus modality: 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. Only little occipital activation was found in sighted subjects, but the same right-olfactory/left-auditory-verbal hemispheric lateralization was found overall in their brain. This difference between the groups was mirrored by superior performance of the blind in various odor-processing tasks. Moreover, the level of right fusiform gyrus activation during the olfactory conditions was highly correlated with individual scores in a variety of odor recognition tests, indicating that the additional occipital activation may play a functional role in odor processing.

Highlights

When early deprived of its natural inputs a sensory cortex starts receiving and processing inputs in the remaining modalities [1,2,3,4,5,6,7]
No group difference was observed in any of these olfactory and auditory regions, though there was a trend toward stronger activation in SC subjects in the left auditory cortex only (p = 0.06 uncorrected) (Figures S2 and S3). During both olfactory and auditory conditions the occipital cortex was largely activated in early blind (EB) subjects and to a much lesser extent in SC subjects. These activation foci were mostly located within the ventral part of the occipital cortex and included the fusiform gyrus, the lingual gyrus and inferior and middle occipital gyri
We found a dissociation between olfactory and auditoryverbal processing in the occipital cortex (OC) of early blind (EB) subjects; the right fusiform gyrus was most activated during the olfactory conditions and part of the left middle occipital gyrus, located in the posterior part of the ventral lateral occipital complex [54,55] showed a preference for auditory-verbal processing (Figure 2)

Summary

Introduction

When early deprived of its natural inputs a sensory cortex starts receiving and processing inputs in the remaining modalities [1,2,3,4,5,6,7]. A stronger recruitment of the occipital cortex was found during odor detection in blind compared to sighted participants [33], indicating further that the so-called ‘‘visual’’ cortex in the blind acquires non-visual functions While these functional studies of brain activity elucidate some heightened auditory or tactile skills in blind individuals (e.g., enhanced spatial localization) [9,10,13,34,35,36,37,38], there were relatively few attempts to compare, in the same blind subjects, the brain activity elicited by stimuli processed in different sensory modalities [20,23,39]. We tested to what extent the degree of occipital cortex recruitment, if present, would be predictive of individual differences in the behavioral performance of odorprocessing tasks

Methods

Results

Discussion

Conclusion