The effect of tapping finger and mode differences on cortical and subcortical activities: a PET study

Using positron emission tomography (PET), the brain regions recruited for the tapping movement by different fingers and different tapping modes were investigated in ten young healthy volunteers without specific finger training. Auditory-paced (2 Hz) tapping movements were performed by the index (I) or ring (R) finger alone (single-finger tapping) and by the alternate use of the I and middle (M) fingers or the R and little (L) fingers (double-finger tapping). Each subject also provided subjective rankings of perceived task difficulty, as well as muscular fatigue, among the tapping tasks. The activated areas of the brain during tapping by the R finger were more extensive in the frontal and temporal areas, as well as the cerebellum, than during tapping by the I finger. A similar result was revealed for the comparison of the RL and IM finger pairs. The perceived task difficulty, as well as muscular fatigue, was also higher for the R finger or RL finger pair than the I finger or IM finger pair. These results indicate that movement of individual fingers or finger pairs with different levels of task difficulty is represented differently in the structures of cortical and subcortical systems. A comparison of the single- and double-finger modes revealed that in addition to the brain areas activated during single-finger mode, the bilateral dorsal premotor and left primary motor/sensory areas and the right anterior cerebellum were also activated during the double-finger mode. These additional areas could be essential structures for the execution and motor sequence operation of the two fingers.