Roh et al. (2011)

Modules in the Brainstem and Spinal Cord Underlying Motor Behaviors.

Jinsook Roh, Vincent C K Cheung, and Emilio Bizzi.

Previous studies using intact and spinalized animals have suggested that coordinated movements can be generated by appropriate combinations of muscle synergies controlled by the central nervous system (CNS). However, which CNS regions are responsible for expressing muscle synergies remains an open question. We address whether the brainstem and spinal cord are involved in expressing muscle synergies used for executing a range of natural movements. We analyzed the electromyographical (EMG) data recorded from frog leg muscles, before and after transection at different levels of the neuraxis - rostral midbrain (brainstem preparations), rostral medulla (medullary preparations), and the spinal-medullary junction (spinal preparations). Brainstem frogs could jump, swim, kick, and step, while medullary frogs could perform only a partial repertoire of movements. In spinal frogs, cutaneous reflexes could be elicited. Systematic EMG analysis found two different synergy types: (1) synergies shared between pre- and post-transection states, and (2) synergies specific to individual states. Almost all synergies found in natural movements persisted after transection at rostral midbrain or medulla, but not at the spinal-medullary junction for swim and step. Some of pre-transection- and post-transection-specific synergies for a certain behavior appeared as shared synergies for other motor behaviors of the same animal. These results suggest that the medulla and spinal cord are sufficient for the expression of most muscle synergies in frog behaviors. Overall, this study provides further evidence supporting that motor behaviors may be constructed by muscle synergies organized within the brainstem and spinal cord, and activated by descending commands from supraspinal areas.

J Neurophysiol, 2011 (in press)