Hand-side difference in human cortical and subcortical systems involved in preparation and movement for lifting an object with a precision grip: PET studies

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Two positron emission tomography (PET) studies were performed in 18 normal volunteers to investigate regional cortical and subcortical activation induced by the lifting-holding- replacing an object repetitively using a precision grip between the index finger and thumb. In lifting of object, t the primary motor (M1), primary sensory (S1), dorso-caudal premotor (PM), caudal supplementary motor (SMA) and cingulate motor cortices contralateral to the hand used were activated. On the ipsilateral side, activation of the M1, caudal SMA, and inferior parietal (BA40) was found. In the subcortical areas, the bilateral cerebellum, left basal ganglla and thalamus were activated. Object weight-dependent activation was observed in the M1/S1 contralateral to the hand used and to some extent in the ipsilateral cerebellum. The areas responsible for preparatory and execution phases for the current lifting task by right and left hands were also investigated. For the prepare and execute condition, the results were similar to the activated areas for lifting action in the first study. BA40 was, however, activated this time in the left side. For the prepare only condition, left SMA and S1 were the activated areas for the right-hand lifting, and for the execute only condition, left M1/S1, PM and thalamus, and right celebellumwere activated. When these tasks were performed by the left hand, there was nearly a mirror image of activated areas seen in the right hand lifting condition. in the preparation task by the left hand, however, the left SMA, right M1 and basal ganglia were activated. Thus, the left SMA is a common area used for preparation of bilateral motor action in these right hand dominant individuals.