Mareike Grotheer, Postdoc, Stanford University, Department of Psychology
Title: A preference for mathematical tasks outweighs the selectivity for Arabic numbers in the inferior temporal gyrus
Abstract: The ability to perform basic math is crucial for our daily life, yet how our brain supports this skill is not fully understood. Recent research has identified an area in the human inferior temporal gyrus (ITG), which responds more strongly to Arabic numbers relative to other visual stimuli and is hence suggested to be responsible for the visual encoding of numbers. However, surprisingly, other recent studies report activations in the ITG during mathematical tasks, even in the absence of visually presented numbers. To settle this debate, we conducted three fMRI experiments that systematically vary tasks and visual stimuli. We find that mathematical processing, not preference to Arabic numbers, consistently drives both mean and distributed responses in the ITG. While we replicated findings of higher responses to numbers than character-like stimuli during a 1-back task within the ITG, this preference to numbers is abolished when participants are engaged in mathematical processing. In contrast, responses in the ITG are higher when subjects are engaged in adding vs. other tasks on the same stimuli. Critically, higher responses during mathematical tasks vs. other tasks generalize across a wide variety of stimuli including Arabic numbers, number/letter morphs, hands, and dice. Likewise, multivariate pattern analyses reveal that mathematical task but not number stimulus can be successfully and consistently decoded from distributed ITG responses. These data suggest that the ITG is involved in mathematical processing rather than visual processing of numbers. We propose that this region ascribes numerical content to visual inputs, irrespective of the nature of the stimulus.