| dc.description.abstract | The representation and processing of alphanumeric symbols in the brain provides an appealing model system for probing mechanisms of brain function and development. Humans use abstract signs, such as letters and numbers, to efficiently tap into distributed brain networks involved in language and mathematics. The invention of written symbol systems occurred too recently in human history for dedicated brain circuits to have evolved for their used. Remarkably, however, after sufficient learning, numbers and letters are found to engage distinct areas along the ventral visual pathway within the occipitotemporal cortex (OTC), including bilateral regions responsive to numerals and a left-lateralized region responsive to letters. The ventral pathway supports object recognition, housing neural populations that represent “what” an input is (i.e., properties of its identity). In humans and non-human primates, the OTC contains a patchwork of areas whose spatial layout is consistent and largely organized around behaviorally- relevant categories of experience, including regions preferentially involved in processing faces, bodies, places, and manipulable objects. Numbers and letters carve out their respective niches within this pre-existing circuitry but, many outstanding questions remain. For instance, why are symbol areas segregated and consistently localized where they are? How and when do they come to acquire their preference for one set of symbols versus another? In this dissertation, I used symbol processing in the ventral stream as a model system for understanding how human learning interacts with innate brain architecture. Our findings were consistent with the idea that long-range connectivity patterns, in terms of axonal wiring and regional communication, determine the location and lateralization of newly-acquired functions in the brain. We further found that brain areas preferentially engaged by Arabic numerals in adults become increasingly tuned to numerals as children go through school, providing novel evidence of experience-dependent plasticity. Our work speaks to several theories of brain organization and development, but perhaps more importantly, opens the door to a number of future directions. | |
