Differential activity in the premotor cortex subdivisions in humans during mental calculation and verbal rehearsal tasks: a functional magnetic resonance imaging study.

To investigate a possible role of the lateral premotor cortex in human cognitive processes, we compared brain activity during mental-operation numeral (MO-numeral) and verbal rehearsal (VR) tasks, using block-design functional MRI. Sixteen healthy subjects serially added a series of single-digit numbers during the MO-numeral task and silently rehearsed a memorized seven-digit number during the VR task. Each task condition was contrasted with a visual fixation task. Both MO-numeral and VR tasks revealed activity within the lateral premotor cortex among others. The rostral and dorsal part of the lateral premotor cortex (PMdr) showed significantly greater activity during the MO-numeral task than the VR task whereas its caudal part (PMdc) was similarly active during the two tasks. The present study suggests that the PMdr and PMdc are involved in different non-motor cognitive processes.