Caltech Research Helps Paraplegic Man Stand and Move Legs Voluntarily

A team of researchers from the University of California, Los Angeles (UCLA), the California Institute of Technology (Caltech), and the University of Louisville have used a stimulating electrode array to assist a paralyzed man to stand, step on a treadmill with assistance, and, over time, to regain voluntary movements of his limbs. The electrical signals provided by the array, the researchers have found, stimulate the spinal cord's own neural network so that it can use the sensory input derived from the legs to direct muscle and joint movements. Rather than bypassing the man's nervous system to directly stimulate the leg muscles, this approach takes advantage of the inherent control circuitry in the lower spinal cord (below the level of the injury) to control standing and stepping motions.

The study is published today in the British medical journal The Lancet.

More than 5.6 million Americans live with some form of paralysis; of these, 1.3 million have had spinal-cord injuries, often resulting in complete paralysis of the lower extremities, along with loss of bladder and bowel control, sexual response, and other autonomous functions.

The work originated with a series of animal experiments beginning in the 1980s by study coauthors V. Reggie Edgerton and Yury Gerasimenko of the David Geffen School of Medicine at UCLA that ultimately showed that animals with spinal-cord injuries could stand, balance, bear weight, and take coordinated steps while being stimulated epidurally—that is, in the space above the dura, the outermost of the three membranes that cover the brain and spinal cord.

Starting eight years ago, Joel Burdick, a professor of mechanical engineering and bioengineering at Caltech, teamed with the Edgerton lab to study how robotically guided physical therapy and pharmacology could be coupled to better recover locomotion in animals with spinal-cord injuries

Building upon these studies and the earlier work of Edgerton and Gerasimenko, Burdick and Yu-Chong Tai, a Caltech professor of electrical engineering and mechanical engineering, introduced the concept of high-density epidural spinal stimulation, which uses sheet-like arrays of numerous electrodes to stimulate neurons. The goal of the system, Burdick says, "is to stimulate the native standing and stepping control circuitry in the lower spinal cord so as to coordinate sensory-motor activity and partially replace the missing signals from above"—that is, from the brain—"and shout 'get going!' to the nerves."

To test this concept, which was first explored in animal models, the team used a commercially available electrode array, which is normally used to treat back pain. While this commercial array does not have all of the capabilities of the arrays tested so far in animals, it allowed the team to test the viability of high-density epidural stimulation in humans. The results, Burdick says, "far exceeded" the researchers' expectations.

The subject in the new work is a 25-year-old former athlete who was completely paralyzed below the chest in a hit-and-run accident in July 2006. He suffered a complete motor injury at the C7/T1 level of the spinal cord, but retained some sensation in his legs.

Before being implanted with the epidural stimulating array, the patient underwent 170 locomotor training sessions over a period of more than two years at the University of Louisville's Frazier Rehab Institute. In locomotor training, a rehabilitative technique used on partially paralyzed patients, the body of the patient is suspended in a harness over a moving treadmill while trained therapists repeatedly help manipulate the legs in a repetitive stepping motion.

The training had essentially no effect on this patient, confirming the severity of his spinal injury. The training also established a "baseline" against which the subsequent efficacy of the electrical stimulation could be measured.