Microelectrode Spinal Implants to Control Paralyzed Limb Function

Researchers from the University of Alberta in Canada have used novel platinum/iridium microelectrodes to create a functional map of the lower spinal cord in monkeys, demonstrating how different segments of the spinal cord control lower limb movement.

This development may one day be used for rehabilitation of patients with paralysis.

The spinal cord is a complex part of our nervous system, regulating our breathing, gait, and bowels. Thus, stimulation of the spinal cord has been studied for re-animating paralyzed limbs and improving recovery. In order to have controlled, intended effects, many researchers have studied the organizational structure of feline spinal cords. However, these differ significantly from human spinal cords, so to address this issue, the Alberta researchers used an implantable microelectrode to study the spinal cord organization of macaque monkeys.

The researchers used platinum/iridium microelectrodes (75 µm diameter) along with a spine-mounted stereotactic system for highly precise spatial control of microelectrode placement. The electrodes were placed in 3D every 2 mm in one direction and every 0.5 mm in the other two, allowing for high-resolution volumetric mapping. Stimulation of between 10 µA to 300 µA at 50 Hz was used at each location. Limb movements were studied by placing reflective markers at key limb positions and recording with a camera.

The researchers studied four macaque monkeys using this approach, mapping the lower spinal region, between L2 and S1. Their findings were used to create a functional map of the spinal cord, documenting how stimulation at precise points translated into motor movements, including hip flexion and extension, knee flexion and extension, ankle flexion and extension, as well as backward and extensor synergy (movement of hips, knees, and ankles in unison).

“We think that intraspinal stimulation itself will get people to start walking longer and longer, and maybe even faster,” said Vivian Mushahwar, lead author of the study appearing in journal Scientific Reports, and professor at University of Alberta. “That in itself becomes their therapy. Imagine the future. A person just thinks and commands are transmitted to the spinal cord. People stand up and walk. This is the dream.”