Recruitment of the occipital cortex by arithmetic processing follows computational bias in the congenitally blind

Abstract

Arithmetic reasoning activates the occipital cortex of congenitally blind people (CB). This activation of visual areas may highlight the functional flexibility of occipital regions deprived of their dominant inputs or relate to the intrinsic computational role of specific occipital regions. We contrasted these competing hypotheses by characterizing the brain activity of CB and sighted participants while performing subtraction, multiplication and a control letter task. In both groups, subtraction selectively activated a bilateral dorsal network commonly activated during spatial processing. Multiplication triggered activity in temporal regions thought to participate in memory retrieval. No between-group difference was observed for the multiplication task whereas subtraction induced enhanced activity in the right dorsal occipital cortex of the blind individuals only. As this area overlaps with regions showing selective tuning to auditory spatial processing and exhibits increased functional connectivity with a dorsal "spatial" network, our results suggest that the recruitment of occipital regions during high-level cognition in the blind actually relates to the intrinsic computational role of the activated regions.

Neural basis of approximate number system develops independent of visual experience

“…The present findings are consistent with prior evidence that the rMOG acquires responses to symbolic number in blindness (Amalric et al, 2017;Crollen et al, 2019;Kanjlia et al, 2016). Like the IPS, the rMOG of blind individuals responds preferentially during math calculation than sentence comprehension and activity increases with the difficulty of math equations (Kanjlia et al, 2016).…”

“…Congenitally blind individuals show similar or slightly better performance than sighted individuals when estimating numbers of tones, footsteps or finger taps, and performance is ratio-dependent in both groups . Prior studies also find that, like people who are sighted, individuals who are congenitally blind recruit the IPS during symbolic number reasoning and show similar behavioral correlations between numerical approximation and symbolic math performance across individuals (Amalric et al, 2017;Crollen et al, 2019;Kanjlia, Feigenson, et al, 2018;Kanjlia et al, 2016). Together, these findings suggest that numerical representations are established in the IPS independent of gross differences in sensory experience.…”

“…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.…”

“…It is now known that vision is not required for the development of symbolic number responses in the IPS. In both congenitally blind and sighted individuals, the IPS is more active during math calculation than sentence comprehension and demonstrates sensitivity to the number of digits and algebraic complexity of math equations (Amalric, Denghien, & Dehaene, 2017;Crollen et al, 2019;Kanjlia, Lane, Feigenson, & Bedny, 2016). However, these findings leave open the question of whether the neural basis of our basic approximate number system is preserved in the absence of vision.…”

“…A second goal of the current study was to investigate potential cross-modal recruitment of the visual cortex for approximate number processing. In addition to the IPS, congenitally blind but not sighted individuals recruit parts of dorsal occipital cortex, specifically the right middle occipital gyrus (rMOG), during math calculation (Amalric et al, 2017;Crollen et al, 2019;Kanjlia et al, 2016). Furthermore, like the IPS, the math-responsive area of the "visual" cortex in blind participants was sensitive to the number of digits and algebraic complexity of math equations (Kanjlia et al, 2016).…”