Sensitive period for cognitive repurposing of human visual cortex

Abstract

Studies of sensory loss are a model for understanding the functional flexibility of human cortex. In congenital blindness, subsets of visual cortex are recruited during highercognitive tasks, such as language and math tasks. Is such dramatic functional repurposing possible throughout the lifespan or restricted to sensitive periods in development? We compared visual cortex function in individuals who lost their vision as adults (after age 17) to congenitally blind and sighted blindfolded adults. Participants took part in resting-state and task-based fMRI scans during which they solved math equations of varying difficulty and judged the meanings of sentences. Blindness at any age caused "visual" cortices to synchronize with specific fronto-parietal networks at rest. However, in task-based data, visual cortices showed regional specialization for math and language and load-dependent activity only in congenital blindness. Thus, despite the presence of long-range functional connectivity, cognitive repurposing of human cortex is limited by sensitive periods.

Neural basis of approximate number system develops independent of visual experience

“…Consistent with the current data, relative to other ventral visual areas, the rMOG of sighted individuals shows higher resting-state synchrony with math-responsive IPS (Kanjlia, Pant, & Bedny, 2018). It is possible that this communication enables some number-related responses in the rMOG of sighted individuals, such as the numerosityspecific patterns observed in the current study.…”

“…It is possible that this communication enables some number-related responses in the rMOG of sighted individuals, such as the numerosityspecific patterns observed in the current study. However, when bottom up visual input is completely removed, these network-specific fronto-occipital connectivity biases are enhanced (Bedny, Pascual-Leone, Dodell-Feder, Fedorenko, & Saxe, 2011;Crollen et al, 2019;Kanjlia et al, 2016;Kanjlia, Pant, et al, 2018). Thus, despite a common preexisting "blue-print," early experience alters the functional properties of cortex, engendering ratio-dependent number coding in parts of cortex that do not typically represent this information.…”

Dysfunctional and compensatory brain networks underlying math fluency

“…While we cannot rule out that AG-associated arithmetic fact retrieval has not also occurred, we posit that it may be more likely a distinct compensatory mechanism involving FFG and associated ventral networks is also engaged in maintained math fluency performance, distinct from arithmetic fact retrieval. Indeed, the engagement of ventral high-level visual areas have also recently been found during math tasks in individuals with congenital blindness, suggesting plasticity in these functions (Kanjlia et al, 2019), that we posit may also occur to beyond individuals with visual impairment.…”

Spoken language comprehension activates the primary visual cortex

“…There is abundant evidence for increased activation of visual cortex for language tasks in early onset blindness as compared to sighted people (Abboud and Cohen, 2019; Bedny et al, 2011a; Burton, 2003; Burton et al, 2003; Burton et al, 2002b; Lane et al, 2015; Röder et al, 2002), suggesting a role for local reweighting and better utilization of inputs. Similarly, evidence for differences in the extent of recruitment depending on the timing of blindness onset also suggests that early-onset blindness involves more than unmasking, and that such additional processes are time-sensitive (Bedny et al, 2011b; Burton et al, 2003; Burton and McLaren, 2005; Burton et al, 2002a; Burton et al, 2002b; Cohen et al, 1999; Kanjlia et al, 2018). However, our results reveal a key piece of this puzzle by explaining how language information arrives in early visual cortex.…”