Cerebral cortical neuronal mechanisms of reaching movements

The planning and control of reaching movements requires the processing of many different types of information, including target location in three dimensions, the starting posture and orientation of the body relative to the target, external forces or loads to be surmounted, the spatial trajectory of movement, skeletomuscular mechanical and contractile properties, and reafferent signals generated by the movement. The neuronal discharge patterns of cells in several cortical regions during reaching movements have been compared in an attempt to define the parameters of movement encoded by their activity and thus their position within the hypothesized planning hierarchy. Observations from two specific areas, the primary motor cortex and the superior parietal cortex, are summarized. A task in which monkeys were trained to make reaching movements in different directions to displace a handle between targets on a target panel was used. The purpose was to identify the reference frame in which movement was encoded in each area, by controlling parameters of movement kinematics and dynamics. However, the specific parameters signaled by the cells were not identified