Comparison of auditory, somatosensory, and visually instructed and internally generated finger movements: A PET study

We sought to determine how the pattern of cerebral activation, and in parti cular in frontal motor areas, during the performance of conditional motor t asks is dependent upon the modality of instruction (visual, auditory, or so matosensory). Regional cerebral blood flow (rCBF) changes with externally i nstructed movements were also compared with internally generated, self-pace d, movements. We used positron emission tomography (PET) with the tracer (H 2O)-O-15 to measure rCBF in 22 healthy volunteers, External stimuli consist ed of the randomized presentation of single or double impulses using a sing le modality for each condition. In the movement scans, the subjects used th e index and middle fingers of their right hands to press a left button for a single and a right button for a double impulse, respectively. In the cont rol scans, subjects were required to covertly distinguish a single from a d ouble stimulus without a motor response. Data were analyzed using conventio nal subtraction techniques with a statistical threshold of Z > 2.33 with co rrections for multiple comparisons. When the activation differences between the three externally instructed movement conditions were statistically com pared, nonsignificant trends toward increased rCBF in the sensory cortex of the modality of the cue were observed but no differential activity in cort ical motor areas. Internally generated movements, when compared to external ly triggered movements, were associated with enhanced activation in bilater al medial and lateral premotor, dorsolateral prefrontal and superior pariet al regions, largely confirming previous reports. The data indicate that, on a regional level, modality-specific processing in a conditional motor task does not occur in frontal motor areas and is probably confined to sensory areas. (C) 2001 Academic Press.