Temporal-spatial deciphering mental subtraction in the human brain

While mental arithmetic has been extensively studied, the precise spatiotemporal neural dynamics of mental subtraction remain poorly understood. This study aimed to decipher the neural mechanisms and chronological brain activity patterns underlying mental subtraction using high-resolution intracranial stereoelectroencephalography (SEEG).

The researchers recorded SEEG data from 20 patients with pharmacologically resistant epilepsy. Participants performed two delayed match-to-sample tasks: one involving simple numeric comparison and another involving mental subtraction. By comparing these tasks, the authors isolated the specific time window and cortical regions involved in the subtraction process, distinguishing them from general numeric processing and attentional demands.

The study identified a critical time window for mental subtraction, spanning 182 ms to 322 ms after the presentation of the second stimulus. Before this window, anterior brain regions (including the frontal, insular, and parahippocampal cortices) were primarily involved in preparation and strategy selection. During the critical window, activity shifted to a posterior network, specifically the parietal, cingulate, and temporal cortices. The researchers found that gamma and beta/gamma band activities in five core regions—the supramarginal gyrus, angular gyrus, cingulate gyrus, fusiform gyrus, and middle temporal gyrus—mediated the subtraction process in a chronological sequence. This suggests a causal flow of information within this network that is distinct from simple numeric comparison.

This research provides the first high-resolution spatiotemporal map of mental subtraction in the human brain. By identifying the specific frequency bands and cortical regions that coordinate to perform subtraction, the study offers new insights into the neurocognitive architecture of mathematical cognition. These findings bridge the gap between static imaging data and the dynamic, millisecond-by-millisecond processing required for complex mental arithmetic.