Thesis (Ph. D.)--University of Rochester. Department of Brain and Cognitive Sciences, 2014.
Living in today's society demands a functional control of math. Recent research suggests that adult mathematical skill is founded on an ontogenetically early emerging number sense, or ability to approximately estimate quantities. This ability is shared with many species, suggesting it represents a core and primitive approximate number system (ANS). Neuroimaging research in both monkeys and humans has linked the ANS to the to the neural responses of the intraparietal sulcus (IPS). As children mature, learn to count and calculate, the BOLD responses of the IPS bear the ratio-dependent signature of the approximate number system. These neural responses show longitudinal profiles that suggest the ANS is relatively stable and sharpens its numerical representations across development in a way that predict their behavioral performance (Emerson & Cantlon, 2014). Children also show math-specific functional connections between the IPS and areas of frontal cortex (Emerson & Cantlon, 2012). This suggests that the IPS plays a role in fine-tuning number and math skills during development. In adults, we have observed a segregation of number-related processes vs other quantitative processes (size/brightness) in the IPS. Regions of the IPS that show a selective response to number overlap with regions that show a ratio-dependent response profile, defining the right IPS as an area of the brain that supports non-verbal numerical skill. Furthermore, we find that cortical thickness correlates with scores on standardized math assessments (SAT) in an area of the right IPS, overlapping regions that are functionally related to number skill. In other words, anatomical and functional variability in the IPS is related to both the ANS and math skill in typical adults. When we tested this region in people with advanced math training, we observed both a heightened neural response to numerical ratio as well as significantly thinner cortex in the depth of the IPS. Compared to typical adults, experts are showing a stronger response of the ANS as well as thinner cortex in a region that correlates with math skills in non-experts (Emerson, Vo, Lussier, Kurtz, & Cantlon, submitted). Taken together, these data converge on the conclusion that our uniquely human ability to use symbolic arithmetic is critically linked to our primitive approximate number skill through a shared neural substrate in the intraparietal sulcus.
