Electrical stimulation of the spinal cord is a promising method to restore voluntary motor function after the impairment of descending pathways through spinal cord injury (SCI) or stroke. However, the neural circuits located above and below the lesion retain their functions. The disruption of descending pathways including the corticospinal tract (CST) results in the loss of connection between the brain and spinal networks and the consequent loss of voluntary motor function. These results suggest that the corticospinal interface can replace the function of the corticospinal tract after spinal cord injury. Thus, monkeys were able to modulate the wrist torque of the paralyzed forearm by modulating the firing rate of M1 neurons including unlinked and linked neurons via the corticospinal interface. Unlinked neurons, which were independent of spinal stimulation and located in the vicinity of the linked neurons, exhibited task-related or -unrelated activity. Linked neurons showed task-related activity that modulated the magnitude of the evoked torque and the activation of multiple muscles depending on the required torque. We then employed the corticospinal interface designed to detect the firing rate of an arbitrarily selected “linked neuron” in the forearm territory of the primary motor cortex (M1) and convert it in real time to activity-contingent electrical stimulation of a spinal site caudal to the lesion. The magnitude of the evoked torque could be modulated by changing current intensity.

Subdural spinal stimulation of the preserved cervical enlargement activated multiple muscles on the paralyzed forearm and wrist torque in the range from flexion to ulnar-flexion. We investigated the feasibility of closed-loop brain-controlled subdural spinal stimulation through a corticospinal interface for the modulation of wrist torque in the paralyzed forearm of monkeys with spinal cord injury at C4/C5. The corticospinal tract plays a major role in the control of voluntary limb movements, and its damage impedes voluntary limb control. 2Division of Neural Engineering, Graduate School of Medical and Dental Sciences, Niigata University, Niigata, Japan.1Neural Prosthetics Project, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan.Kei Obara 1,2, Miki Kaneshige 1, Michiaki Suzuki 1, Osamu Yokoyama 1, Toshiki Tazoe 1 and Yukio Nishimura 1,2*

Emg cervical spine