Impact of early versus late acquired blindness on the functional organization and connectivity of the occipital cortex

Abstract

Recent studies demonstrated that auditory processing in the reorganized occipital cortex of congenitally blind (CB) humans maintains some level of specialization that is known to characterize the occipital cortex of sighted individuals. A crucial yet unresolved question concerns the existence of a sensitive period in order for such specific reorganization to occur. Therefore, we investigated the impact of early versus late visual deprivation in shaping the functional properties of the occipital cortex. Using functional magnetic resonance imaging (fMRI), we characterized brain activations of CB and late blind (LB) subjects when they processed either the pitch or the spatial attributes of sounds. Our data demonstrates massive recruitment of occipital regions for auditory processing in both blind groups relative to matched sighted groups, although the extent was less widespread in LB when compared to CB. Intriguingly, some auditory activity in the occipital cortex observed in LB was inversely proportional to blindness duration. We also observed that some regions of the right dorsal stream (lateral occipito-temporal and cuneus) were preferentially activated for the spatial processing of sounds in CB only. This suggests that vision has to be lost during an early sensitive period in life in order to transfer its functional specialization for space processing toward a non-visual modality. Finally, dynamic causal modeling revealed that different architectures of cortical pathways underlie auditory activity in primary occipital cortex of CB and LB. Altogether, these results demonstrate important quantitative and qualitative changes in the cortical reorganizations observed in the CB and LB, unraveling the critical role of early versus late experience in shaping the functional architecture of the occipital cortex. These results are clinically important now that a growing number of therapeutic interventions may restore vision after a period of visual deprivation.

Meeting abstract presented at VSS 2012