Paul D. Cheney, Ph.D.

Brain Control of Movement: We investigate basic neural mechanisms underlying the control of voluntary movement and recovery of motor function following brain injury. Some general questions we are working on include: 1) How are synaptic connections between single corticospinal neurons and motoneurons of agonist and antagonist muscles organized? 2) Do the synaptic connections of corticospinal neurons represent combinations of muscles that function as functional synergies in the performance of skilled, multi-joint voluntary movements? 3) What is the relative efficacy of output effects on muscle activity from different premotor cortical areas in comparison to primary motor cortex? 4) How does motor output from cortex vary as a function of electrical stimulation parameters?

Nearly all of our work relies on use of monkey models. Monkeys provide a number of important advantages most important of which is the fact the monkey brain is similar to the human brain in terms of the control of movement. Our primary methodological approach involves training monkeys to make limb movements of interest (Fig. 1). Once trained, a recording chamber is attached to the skull through which microelectrodes can be inserted into the brain for the purpose of recording the spike (action potential) activity of single neurons and for electrical stimulation of highly localized areas in the vicinity of the electrode tip. We also record the electromyographic (EMG) activity of as many as 24 forelimb muscles. Both neuronal and muscle activity are recorded simultaneously while the monkey performs voluntary movements of the limbs (Fig. 1).

Figure 1. Monkey trained to make wrist movements alternating between target zones in flexion and extension. The activity of cortical neurons is recorded simultaneously with EMG activity of multiple muscles. Spike and stimulus triggered averaging of EMG activity is performed to reveal the synaptic organization of corticospinal output.

Figure 2. Representation of distal and proximal muscles of the forelimb in primary motor cortex in the monkey derived from stimulus triggered averaging of EMG activity. Maps are show for two monkeys. Colors represent cortical sites evoking output effects in distal only, proximal only or combinations of distal and proximal muscles. Results demonstrate a consistent somatotopic organization in the representation of forelimb muscles and a zone representing combinations of distal and proximal muscles.