Relations between two-dimensional arm movements and single cell discharge in motor cortex and area 5: Movement direction versus movement endpoint

Experimental Brain Research - 1985-01-01Georgopoulos AP, Kalaska JF, Caminiti R
An important question regarding the CNS mechanisms subserving the control of movement in space concerns the variable to which changes in cell discharge preceding movement onset might be related, that is, the behavioral variable predicted by these changes. In the case of aimed movements this question assumes a special significance, for specific hypotheses have been put forth on how the motor system might produce them. According to one idea, what matters is the final position of the arm (Polit and Bizzi 1979): according to another, it is the particular parameters of movement (e.g., direction) that are programmed (Rosenbaum 1980). Apparently, both factors are of importance. For example, information about the location of the target, and therefore the end point of the movement, has to be taken into account, even if movement parameters have to be calculated. On the other hand, movements with certain specifications (e.g., to be made in a desired direction) can be produced at will without reference to a target. It is likely that in CNS motor structures both kinds of relations, that is, to the target and/or to the parameters of the upcoming movement, can be found, depending on the structure under study and the conditions of the task. We explored these relations in two cortical areas involved in the central control of movement, namely, the motor cortex and area 5 of the posterior parietal cortex, under conditions that dissociated the target of the movement from its direction.