Using tools, writing, and eating are all important behaviors that involve manipulating objects. Successful manipulation requires the control of both the force exerted on the object and its resultant motion. Both have been associated with neural activity in the motor cortex and we are interested in the extent to which neural firing rates in this brain region are related to their combined control. The mechanical relation between force and motion is impedance and we hypothesized that motor cortical activity encodes an impedance signal that reflects the force and motion demands of behavior. We examined this possibility with a paradigm in which subjects manipulated a handle that moved along a track. The handle was locked in place until the subject exerted enough force to cross a specific threshold; it was then released and moved along the track. We hypothesized that this ballistic-release task would encourage subjects to modify their arm impedance in anticipation of the upcoming movement.
We modeled the behavior as a physical dynamical system and found that one component of model impedance, stiffness, varied in a way that matched the behavioral demands of the task and that stiffness could be dissociated from changes in force and displacement. We recorded activity from a population of motor cortical neurons and found that the temporal and time-averaged neural responses encoded information about motion and force. We also could decode model impedance parameters that we then used to approximate the time-varying force exerted on the handle. The force exerted on the handle and the model stiffness depended on muscle activity and we found components of muscle activity related to both force and model stiffness. Additional components of motor cortical activity were also related iv to both force and stiffness, suggesting a possible parceling of muscle-related representations in motor cortical activity. In addition to extending current models of neural activity to include manipulations, this study may be helpful in understanding how information encoded in motor cortical activity might be transformed into muscle activity during object interaction.
|Commitee:||Hogan, Neville, Loughlin, Patrick, Schwartz, Andrew, Strick, Peter|
|School:||University of Pittsburgh|
|School Location:||United States -- Pennsylvania|
|Source:||DAI-B 80/05(E), Dissertation Abstracts International|
|Subjects:||Neurosciences, Biomedical engineering|
|Keywords:||Impedance control, Motor control, Motor cortex, Object manipulation|
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