With the intention of delivering electricity directly to a human spine, Harkema repurposed a medical device that was originally designed to suppress pain. The device, consisting of 16 electrodes packaged in a tiny array a few centimeters long, would be surgically implanted into a patient’s lower back, just over the dura — the outermost of three layers of membranes surrounding the spinal cord.
Wires would lead from the array to a small, rectangular neurostimulator device that packed a charge. This would be implanted beneath the skin in the lower back. Just as Edgerton’s device activated the rats’ nervous systems, Harkema’s rechargeable and programmable device would tell the electrodes connected to the dura how much electricity to apply to neurons in the lower spinal cord, and how often.
Once those neurons fired, they would remember how to communicate with each other, and with muscles as well. Over time and with training, patients who had lost a connection between the spinal cord and the brain would use a remote control to communicate conscious instructions to the device.
But before this technique could advance, Edgerton and Harkema needed a patient and FDA approval.
Off the Bench
After his injury, Summers, still a ballplayer at heart, started doing his own research to find a spinal cord therapy program that emphasized exercise-based training. In 2007, he met Harkema and moved to Louisville.
By 2009, Edgerton’s work had shown enough promise for the FDA to approve his and Harkema’s request to do a set of human experiments with the electrode device. The test subjects would need to have a completely severed spinal cord, with no motor activity below the waist. And they would need to be able to perform many long and potentially grueling physical experiments to try to replicate the success Edgerton saw in his rats.
The subjects would have to spend hours on the treadmill, just to make sure there was no chance of recovery with physical training alone. The rigor involved would require someone with both strength and perseverance. Summers, the former college athlete, was a perfect fit.
Harkema and her team first worked with Summers on locomotor training, without electrical stimulation. As expected, there was no improvement in Summers’ ability to stand or move below the level of his spinal cord injury.
In late 2009, Harkema and Edgerton’s team implanted the electrode array directly over Summers’ dura. The neurostimulator device and remote-controlled mechanism still bulge out like a small stack of business cards on the lower right side of his back.
A few weeks after recovering from the surgery, Summers arrived in the lab, expecting a long process of fits and starts. But on just his first attempt to stand, the electrode array got Summers’ neurons talking. A researcher turned on the neurostimulator. Strapped into a harness and attached to sensors, Summers was lowered over a treadmill.
As his feet touched down and his lower body started to feel his weight, Summers’ legs engaged — just as the rats’ legs did in Edgerton’s earlier treadmill experiments. The trainers stabilized Summers during this process, but as he stood upright on the treadmill, they slowly took their hands off him, until he was standing alone. “Everyone was in shock,” Edgerton recalls.
Summers was standing upright, carrying a third of his own weight on two legs, the interneurons in his spinal cord now electrically stimulated, shouting directives to his motor neurons and muscles to stand straight. Slowly and jerkily, Summers’ body started to regrasp very basic but astounding control.
With the electrode array turned on, the spinal cord was awakened. It could receive and process sensory information again. With the help of the electrodes, it could sense that there was pressure on the soles of Summers’ feet, and it could react.
As it awoke, Summers’ spinal cord became more and more perceptive. Summers was consciously creating the preconditions for his body to stand, by weighting his feet, but he wasn’t consciously doing the standing. Edgerton calls it “indirectly voluntary” and notes that this combination of conscious and automatic activity is shaking up the way researchers think about movement.