Producing motor actions requires orchestrated activation across the entire motor system. This coordinated neural activity is obtained via massive interactions between several motor-related centers, including the motor cortex, spinal cord, cerebellum and brainstem nuclei. The importance of these interactions becomes evident when the normal flow of information between these sites is interrupted. In these cases (e.g., spinal cord injury, spinocerebellar ataxia, etc.) damage to connecting pathways interrupts the normal operation of the motor system and leads to severe motor deficits. In these cases, the neurons are often intact, yet the information they receive is greatly altered.
In my lab we are studying the flow of information in the motor system and its contribution to the emergence motor of commands and subsequently motor actions. Our working hypothesis is that different sources of motor-related information regulate unique aspects of motor commands (e.g., selected actions, target direction and timing of action). These sources of information converge upon motor cortical circuitry according to some yet unknown principles of connectivity. The resultant motor cortical command is an integrated transient signal which is further modified at the spinal level before finally reaching working muscles.
Using parallel recording from multiple motor hierarchies (i.e., motor cortex, motor thalamus, spinal cord and muscles) and employing protocols of electrical stimulations we identify the connectivity pattern between different sites, and thus measure the information transmitted between these sites. Interrupting with the flow of information between sites using chronically implanted electrodes highlights the events which take place during pathological states. By working with behaving primates we can study the operation of the motor system both in health and disease in a model closest to humans.
To-date we focused on the descending control exerted by motor cortex over spinal circuitry before and during voluntary movements. We found that corticospinal (CS) interactions are extensive and dynamics and can act as a processing link for modifying the cortical motor command into an appropriate activation signals for muscles. We further found that CS connectivity of motor and premotor cortex can exert a dual, priming and breaking, impact on spinal circuitry. This mechanism can serve as a gating signal that prevents a pre-mature release of movements. These results re-define the hierarchical organization of motor cortex and spinal circuitry during voluntary movements.
Our current research focuses on the complementary direction of information flow, namely the thalamocortical (TC) impact on motor cortex. Here we characterize the connectivity of the TC system in the motor system of primates, and its implication on cell activity and cell-to-cell interactions. Moreover, we are now able to replicate the behavioral events which take place during cerebellar ataxia and measure the neural correlates of these changes.