Cortical activity in precision- versus power-grip tasks: An fMRI study

Most manual grips can be divided in precision and power grips on the basis of phylogenetic and functional considerations. We used functional magnetic resonance imaging to compare human brain activity during force production b y the right hand when subjects used a precision grip and a power grip. Duri ng the precision-grip task, subjects applied fine grip forces between the t ips of the index finger and the thumb. During the power-grip task, subjects squeezed a cylindrical object using all digits in a palmar opposition gras p. The activity recorded in the primary sensory and motor cortex contralate ral to the operating hand was higher when the power grip was applied than w hen subjects applied force with a precision grip. In contrast, the activity in the ipsilateral ventral pre motor area, the rostral cingulate motor are a, and at several locations in the posterior parietal and prefrontal cortic es was stronger while making the precision grip than during the power grip. The power grip was associated predominately with contralateral left-sided activity, whereas the precision-grip task involved extensive activations in both hemispheres. Thus our findings indicate that in addition to the prima ry motor cortex, premotor and parietal areas are important for control of f ingertip forces during precision grip. Moreover, the ipsilateral hemisphere appears to be strongly engaged in the control of precision-grip tasks perf ormed with the right hand.