Abstract
It is well established that the human brain reorganizes following sensory deprivations. In blind individuals, visual processing regions including the lateral occipital cortex (LOC) are activated by auditory and tactile stimuli as demonstrated by neurophysiological and neuroimaging investigations. The mechanisms for such plasticity remain unclear, but shifts in connectivity across existing neural networks appear to play a critical role. The majority of research efforts to date have focused on neuroplastic changes within visual unimodal regions, however we hypothesized that neuroplastic alterations may also occur in brain networks beyond the visual cortices including involvement of multimodal integration regions and heteromodal cortices. In this study, two recently developed graph-theory based functional connectivity analyses, interconnector analyses and local and distant connectivity, were applied to investigate functional reorganization in regional and distributed neural-systems in late-onset blind (LB) and congenitally blind (CB) cohorts each compared to their own group of sighted controls. While functional network alterations as measured by the degree of differential links (DDL) occurred in sensory cortices, neuroplastic changes were most prominent within multimodal and association cortices. Subjects with LB showed enhanced multimodal integration connections in the parieto-opercular, temporoparietal junction (TPJ) and ventral premotor (vPM) regions, while CB individuals exhibited increased superior parietal cortex (SPC) connections. This study reveals the critical role of recipient multi-sensory integration areas in network reorganization and cross-modal plasticity in blind individuals. These findings suggest that aspects of cross-modal neuroplasticity and adaptive sensory-motor and auditory functions may potentially occur through reorganization in multimodal integration regions.
Highlights
Unimodal and Multimodal Interconnectivity in late-onset blind (LB) and congenitally blind (CB) Subjects Compared to their Matched Controls
We found that LB and CB subjects compared to matched controls (MCs) demonstrated enhanced functional connections that potentially underlie aspects of sensory adaptive phenomena after visual deprivation
These findings suggest that while functional alterations occurred in unimodal cortices including the lateral occipital cortex (LOC), extensive neuroplastic changes in blind individuals occurred at the level of multimodal and higher-order integrative processing regions
Summary
Cross-modal neuroplasticity has been proposed as a fundamental mechanism by which individuals without sight recruit visualrelated cortices to process sensory information from other perceptual sensory modalities (Amedi et al, 2003; Merabet et al, 2004; Bedny et al, 2011; Ortiz et al, 2011; Watkins et al, 2013). Functional imaging studies in late-onset blind (LB) and congenitally blind (CB) subjects have shown that, regardless of task and age of onset, there is consistent activation of brain areas such as the lateral surface of the occipital cortex (LOC) during auditory and/or tactile sensory tasks These findings suggest cross-modal plasticity in visual-related cortices (Amedi et al, 2003; Bedny et al, 2011) in blind subjects, as many studies have shown using whole brain task analyses with different functional neuroimaging techniques (Supplementary Figure S1 shows the main activation foci of previous cross-modal, task-based studies that used a wholebrain analytical approach). Reorganization of functional connections between the perceptual cortex and heteromodal areas have been recently reported (Bedny et al, 2011; Burton et al, 2014)
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