Spinal cord microstimulation generates functional limb movements in chronically implanted cats

Spinal cord injuries disrupt the communication between the brain and periph eral nerves, but leave motoneurons and networks of interneurons below the l evel of the lesion intact. It is therefore possible to restore some functio n following injury by providing an artificial stimulus to the surviving neu rons below the level of the lesion. We report here on a novel approach for generating functional movements by electrically stimulating the spinal cord through chronically implanted ultrafine, hair-like electrodes. Six to 12 m icrowires were implanted in the lumbar enlargement of intact cats for 6 mon ths. Twice a week, trains of stimuli were delivered through each microwire and the evoked electromyographic and torque responses were recorded. Strong coordinated hindlimb movements were obtained by stimulating through indivi dual electrodes. The joint torques elicited were capable of supporting the animals' hindquarters. The responses were stable over time and the contract ions caused no apparent discomfort to the animals. No obvious motor deficit s were seen throughout the 6-month duration of implantation. The results de monstrate that microwires implanted in the spinal cord remain stably in pla ce and stimulation through these electrodes produces strong, controllable m ovements. This provides a promising basis for the use of spinal cord neurop rostheses in restoring mobility following spinal cord injury. (C) 2000 Acad emic Press.