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Shipra Kanjlia, Lisa Feigenson, Marina Bedny; A critical period for number-related plasticity in the visual cortex of blind individuals. Journal of Vision 2017;17(10):644. doi: 10.1167/17.10.644.
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Recent studies suggest that visual cortices are highly functionally flexible, responding not only to non-visual sensory tasks, but also to high-level linguistic and mathematical tasks in congenitally blind individuals (Bedny et al., PNAS, 2011; Kanjlia et al., PNAS, 2016). Specifically, middle occipital gyri are recruited for numerical processing and are sensitive to math difficulty in congenitally blind and not sighted individuals. Is such extreme cortical flexibility unique to a critical period early in development? We asked whether visual cortex plasticity for numerical processing differs across individuals who have been blind from birth and those who became blind as adults. We tested individuals who became blind at 17-years-of-age or later (late blind, LB; n=10; blindness duration: 12-31 years, mean=20.35 years), congenitally blind adults (CB; n=17) and blindfolded sighted controls (S; n=19). Participants underwent fMRI while performing a math task in which they judged whether the value of an unknown variable was the same across two equations (e.g. 7-2=x, 8-3=x). Equations were either single- or double-digit (e.g. 7-2=x vs. 27-12=x) and either algebraically complex or simple (e.g. 7-2=x vs. x-2=7). In a language control task, participants decided if two sentences had the same meaning. Unlike CB individuals, LB individuals do not recruit visual cortices during math calculation more than sighted individuals (whole-brain analysis, p< 0.05, cluster-corrected). Furthermore, CB individuals activate right occipital pole (rOP) more than LB individuals during numerical processing (p< 0.05, cluster-corrected). Region of interest analyses show that in CB but not LB individuals, rOP is sensitive to digit-number (CB: F(1,16)=22.78, p< 0.001; LB: F(1,9)=1.78, p=0.22; group-by-condition interaction: F(1,25)=4.84; p=0.04) and algebraic-complexity (CB: F(1,16)=7.53, p=0.01; LB: F(1,9)=1.26; p=0.29; group-by-condition interaction: F(1,25)=1.94; p=0.18). Thus, only the visual cortices of individuals who are blind from birth are repurposed for numerical processing, supporting the existence of a critical period for visual cortex plasticity.
Meeting abstract presented at VSS 2017
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