Functional dominance of finger flexion over extension, expressed in left parietal activation.

Sensory stimuli may elicit a widely distributed parietal-premotor circuitry underlying task-related movements such as grasping. These stimuli include the visual presentation of an object to be grasped, as well as the observation of grasping performed by others. In this study, we used functional Magnetic Resonance Imaging (fMRI) to test whether the performance of simple finger flexion, contrasted to extension, might similarly activate higher-order circuitry associated with grasping. Statistical Parametric Mapping (SPM) showed that flexion, compared to extension, was related with significant activation of the left posterior parietal cortex and posterior insula, bilaterally. This pattern supported our hypothesis that simple finger flexion has a specific relation with circuitry involved in preparing manual tasks. Although the two motor conditions showed major overlap in the primary motor cortex, increased flexion-related activation at the precentral motor-premotor junction further supported its association with higher-order motor control.