Involvement of the ventral premotor cortex in adaptive reaching movements following dynamic changes of motor frame of reference

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In reaching, a spatial visuomotor transformation should occur in our brain. We can make the transformation not only when the relationship between visual and motor coordinates is default, but also when a gain for the relationship is changed, for example, in a microsurgery. We trained monkeys to make reaching movements when visuospatially identical targets were presented on a computer display by aligning a cursor that indicated their hand position, while the gain was systematically changed. We recorded and analyzed movement-related neuronal activity in the ventral premotor cortex (PMv) and the primary motor cortex (MI) during reaction time. It was revealed that a majority of the MI neurons and a part of the PMv neurons showed activity changes depending on executed movement direction, amplitude, and velocity, whereas a number of the PMv neurons exhibited activity consistent to the visual location of the targets, but not to motor parameters such as amplitude and velocity. Furthermore, introcortical microstimulation in the PMv evoked changes in direction and amplitude (gain) of reaching movements. The results indicate that the PMv contributes to gain control of reaching during visuomotor transformation.