Brain Mechanisms of Arithmetic: A Crucial Role for Ventral Temporal Cortex

Abstract

Mental arithmetic is central to our society, yet the roles of different brain regions involved in calculation remain poorly understood. To tackle this issue, we recorded electrocorticography signals from subjects solving addition problems. Behavioral results showed a classical problem-size effect: RTs increased with the size of the operands. We then examined how high-frequency broadband (HFB) activity is modulated by problem size. Sites around the intraparietal sulculs (IPS) showed increased total activity with problem size, compatible with a role in arithmetic decision making. More surprisingly, sites within the posterior inferior temporal gyrus (pITG) showed an initial burst of HFB activity that decreased with problem size, yet with a constant integral, suggesting that pITG appears to represent the amount of semantic evidence available for a calculation. Our results ask for a re-evaluation of current models of arithmetic and demonstrate that the ventral temporal cortex contain regions involved in symbolic forms of reasoning, such as mental calculation.