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July 2004 Issue

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PM&R Researchers Study How Brain Reroutes Movement Controls

Published July 2004

UC Medical Center scientists are using the latest imaging technology to determine how the brain manages to "change its mind" after certain paralyzing injuries, essentially rerouting its own neural network so that the legs can relearn how to function after injury.

The rerouting phenomenon is believed to occur in patients with "incomplete" spinal cord injuries, in which the cord remains connected to the brain. It works like emergency circuitry patching - the brain automatically switches movement control to a new location when the legs are stimulated.

By studying patients with incomplete injuries, the researchers hope to be able to identify in each patient where the movement control center has shifted to, and then target the new location with interventions that stimulate muscle function.

Early results from four patients are so encouraging, the scientists foresee a potential breakthrough in the care and recovery of spine-injured patients.

What normally happens is that the brain transmits a signal down the spinal cord telling the leg muscles to move. But to determine what changes have occurred in the brain following spinal injury, UC researchers working at the Drake Center are essentially reversing the physiological process.

They stimulate patients' leg muscles using an external electrical source, a StimMaster stationary "bicycle" designed by nationally known electrical stimulation expert Steven Petrofsky.

The StimMaster delivers a series of small electrical charges to the patient's legs, triggering them to pedal. The leg movements in turn send a signal up the still-intact spinal cord pathways to the brain, the reverse of the normal process. This activates the leg-control center - much like pushing a car while it's in gear turns over the engine and fires the spark plugs.

Then, thanks to some highly sophisticated technology in UC's Center for Imaging Research, a 4-Tesla FMRI (functional magnetic resonance imaging) scanner, the researchers can track the neurological signals in the brain to pinpoint the location of the movement control center.

A Tesla is a unit of magnetic field strength, and MRI scanners usually run at 1.5 Teslas. The stronger the magnet, however, the better the images obtained of the structure, chemical processes and function of a patient's brain. UC's 4-Tesla MRI is one of the most powerful in Ohio, and one of only about a dozen in the country.

"When we're working with someone who might not have walked for three or four years," says principal investigator Jonathan Strayer, MD, of the Department of Physical Medicine and Rehabilitation, "we're able to take a picture of the leg-control 'biomarker' in the brain that shows it expanding. That gives us an idea of what's going on, and where it's happening, that allows us to target the brain with other interventions."

This approach is not yet seen as a cure, says Dr. Strayer, who himself has an incomplete spinal injury. But it could lead to a breakthrough in care and recovery by significantly increasing the patient's quality of life.

Spinal cord-injured patients, for example, often become obese from lack of exercise. But the combination of muscle stimulation and exercise can help control weight gain, while at the same time reducing blood pressure, pulse rate and other medical complications and increasing the patient's range of motion.

"And even if we can't get these patients to walk yet," adds Dr. Strayer, "we can give them a better quality of life. One of our patients, for example, although not able to walk, has regained a degree of independence by being able to drive again."

The StimMaster is not only yielding important information about the mechanism of the body's automatic rhythmic movements, and identifying what's going on when it fails, says Dr. Strayer. It's also proving cheaper and more efficient than the standard treadmill for exercise therapy.

A "deconditioned" patient on a treadmill, for example, must be supported in a harness and requires help from several therapists. The equipment is expensive, the therapy exhausting.

Using the StimMaster cycle, however, the patient sits comfortably in a cushioned seat, without requiring mechanical or human physical support.

Another benefit of the cycling might be stimulation of what scientists call the central pattern generator (CPG). This nerve mechanism, thought to be located in the spinal cord, controls rhythmic movements such as walking without brain input.

"Unfortunately," says Stephen Page, PhD, co-principal investigator and research director in physical medicine and rehabilitation, "you can't take the spinal cord apart. And it has no blood flow to take up a contrast medium and generate a visual image, which makes it very tough to figure out."

An important next step, therefore, just as it's done in the brain, is to find a way of generating an image of the spinal cord.

"Science is deliberate," observes Dr. Page. "We can't start on the spine until we understand the effect of spinal injury on the brain. First we need a good marker of what's going on there."So we have to start on things we know, or study people who are less impaired, like our incomplete spinal cord injury patients. When we have this pilot data, it will be reasonable then to move down the spinal cord to see what's going on there."

The research at UC and the Drake Center is currently funded by a two-year, $80,000 grant from the College of Medicine Dean's Discovery Fund.

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