Neuronal Population Responses in the Human Ventral Temporal and Lateral Parietal Cortex during Arithmetic Processing with Digits and Number Words

Past research has identified anatomically specific regions in the posterior inferior temporal gyrus (PITG) and the intraparietal sulcus (IPS) that are engaged during arithmetic processing. In the current study, we explore whether the responses in these regions depends on the number format (i.e., numerical digits vs. number words). We collected intracranial EEG (iEEG) data from the areas surrounding the PITG in eight subjects who performed two experimental tasks containing arithmetic equations with either digits or number words. Our findings confirmed an increase in the high frequency broadband (HFB) activity in both PITG and IPS regions for equations presented in either digits or in number words compared to their respective baselines. In the PITG the HFB activations were similar for digits and number words in the time of activation but differed in magnitude. In the IPS the activity was significantly delayed for number words in comparison to digits regardless of the hemisphere. The results support the extant evidence for the engagement of the PITG during arithmetic processing regardless of input format while also revealing differences in the magnitude of power in response to the formats. The results also reveal that the IPS region becomes engaged regardless of input format but with different temporal signatures. The results add to our understanding of the temporal profile of engagement between discrete populations of neurons within the human brain during arithmetic processing with numerals versus number-words.