Role of primary motor cortex in gait: automatic-voluntary dissociation seen in paretic leg of a patient who had a stroke

OBJECTIVE: To examine the role of primary motor cortex in gait through exploring the dissociation of impaired voluntary leg muscle contraction and preserved rhythmic activities during gait in a patient who had a stroke. SUBJECT AND METHODS: A 49-year-old man with an infarct in the primary motor cortex exhibited automatic-voluntary dissociation in the paretic leg. Functional studies were conducted using surface electromyography (EMG) and near-infrared spectroscopy (NIRS). RESULTS: The patient was incapable of voluntary contraction of individual leg muscles on the paretic right side but was able to walk automatically while contracting those muscles rhythmically. Surface EMG confirmed the earlier findings objectively. The preserved automatic activities helped recovery of gait capability, but NIRS showed no functional recovery in the corresponding motor cortex during treadmill gait. We considered that the loss of voluntary leg muscle contraction and the preserved gait capacity in this patient represented a form of automatic-voluntary dissociation. CONCLUSIONS: The preserved gait capability suggests that the leg representation of the primary motor cortex may not play a major functional role in gait, but other components of the nervous system, including the spinal central pattern generator, would serve important functions to maintain gait capability.