Principal Investigator Emilio Bizzi
We wish to address two questions: what are the organizational principles subserving the control of the hand, and how is this control implemented physiologically? These related research topics have generated two different hypotheses. First, it has been suggested that the complexity of limb control may be simplified by the presence and combinations of fixed patterns of muscle activity. By activating muscles as "synergies," the nervous system would effectively reduce the degrees of freedom associated with the musculoskeletal system. Our project extends the synergy hypothesis to a complex vertebrate system, the primate hand. We will search for synergies in the patterns of electromyographic (EMG) activity observed in a variety of natural movements of the hand.
The second hypothesis, regarding physiological implementation of a modular architecture, is that any synergistic patterns will be reflected in associated cortical activity. How the primate motor cortex represents movements generally - in terms of individual muscles, muscle groupings, or movements - remains unresolved. But while non-hand movements may first be encoded synergistically at the level of the spinal cord, there is evidence that a distributed control system in the cortex is directly responsible for muscle activation patterns of the primate hand. An important innovation of our project is that we plan to combine EMG data from the muscles innervating the hand with simultaneous recordings from the cortex as well as observable hand kinematics. We hope that these concurrent measurements will allow us to localize the origin of synergistic hand control. We are also considering the inclusion of cellular inactivation methods to demonstrate causal relationships between cortical and muscular patterns of activity.