Abstract
Event-related potentials ERPs were used to examine the organization of brain activations during single-digit multiplication. Electrophysiological, neuropsychological, and brain-imaging data suggest that left inferior parietal areas are involved in mental calculation. We aimed at investigating the involvement of this area in simple and difficult single-digit multiplications, and at determining the time course of its activation. ERPs were recorded from 64 channels while subjects performed a sequential multiplication-verification task. Simple and difficult multiplication problems were presented either visually as arabic digits or auditorily as number words. For both modalities of input, a significant effect of difficulty was found on left and right inferior parietal electrode sites. The results suggested that simple multiplication problems may involve a short-lived activation in the left inferior parietal cortex, whereas complex problems may require longer processing which also involves the homologous right area. These findings also demonstrate the significance of ERPs as a tool for determining the temporal orchestration of brain areas involved in a cognitive task.