Increased BOLD variability in the parietal cortex and enhanced parieto-occipital connectivity during tactile perception in congenitally blind individuals

Abstract

Previous studies in early blind individuals posited a possible role of parieto-occipital connections in conveying nonvisual information to the visual occipital cortex. As a consequence of blindness, parietal areas would thus become able to integrate a greater amount of multimodal information than in sighted individuals. To verify this hypothesis, we compared fMRI-measured BOLD signal temporal variability, an index of efficiency in functional information integration, in congenitally blind and sighted individuals during tactile spatial discrimination and motion perception tasks. In both tasks, the BOLD variability analysis revealed many cortical regions with a significantly greater variability in the blind as compared to sighted individuals, with an overlapping cluster located in the left inferior parietal/anterior intraparietal cortex. A functional connectivity analysis using this region as seed showed stronger correlations in both tasks with occipital areas in the blind as compared to sighted individuals. As BOLD variability reflects neural integration and processing efficiency, these cross-modal plastic changes in the parietal cortex, even if described in a limited sample, reinforce the hypothesis that this region may play an important role in processing nonvisual information in blind subjects and act as a hub in the cortico-cortical pathway from somatosensory cortex to the reorganized occipital areas.

Figure 1

Mean squared successive difference (MSSD) significant (corrected P < 0.05) differences between blind and sighted individuals during (a) the tactile spatial discrimination and (b) tactile motion perception experiments. (c) The conjunction map (logical AND) obtained from the thresholded sighted-versus-blind MSSD maps revealed a region located in left inferior parietal and anterior intraparietal cortex (IPL/aIPS) that showed similar differences in signal variability in the tactile spatial and motion discrimination experiments (k > 30 voxels). Spatially normalized MSSD differences are projected onto single-subject left and right hemisphere templates in the Talairach space.

Figure 2

Group functional connectivity (FC) maps obtained for sighted (first column) and blind (second column) individuals during (a) the tactile spatial discrimination and (b) the tactile motion perception tasks (corrected P < 0.05). The third column (c)-(d) shows the differences in functional connectivity between the two groups (uncorrected P < 0.05, k > 30 voxels). The left inferior parietal seed ROI has been indicated with a purple circle. Spatially normalized maps are projected onto single-subject left and right hemisphere templates in the Talairach space in frontal and lateral views. Cun: cuneus; SO: superior occipital; MO: middle occipital; SMa: supramarginal; IP: inferior parietal; ST: superior temporal; AT: anterior temporal.