A Scientist's Pink Cast Leads To Discovery About How The Brain Responds To Disability

A neurologist who encased his healthy right arm in a pink fiberglass cast for two weeks has shown how quickly the brain can change after an injury or illness.

Daily scans of Dr. Nico Dosenbach's brain showed that circuits controlling his immobilized arm disconnected from the body's motor system within 48 hours.

But during the same period, his brain began to produce new signals seemingly meant to keep those circuits intact and ready to quickly reconnect with the unused limb.

Dosenbach, an assistant professor at Washington University School of Medicine in St. Louis, repeated the experiment on two colleagues (their casts were purple and blue) and got the same result. In all three people, the disconnected brain circuits quickly reconnected after the cast was removed.

The study, published online in the journal Neuron, shows that "within a few days, we can rearrange some of the most fundamental, most basic functional relationships of the brain," Dosenbach says. It suggests it is possible to reverse brain changes caused by disuse of a limb after a stroke or brain injury.

The results of the study appear to support the use of something called constraint-induced movement therapy (CIMT), which helps people – usually children — regain the use of a disabled arm or hand by constraining the other, healthy limb with a sling, splint, or cast.

Previous studies of CIMT have produced mixed results, in part because they focused on brain changes associated with increased use of a disabled arm, Dosenbach says. "We looked at the effect of actually not using an arm because we thought that was a much more powerful intervention," he says.

The study adds to the evidence that CIMT works by changing the brain, says Lynne Gauthier, an associate professor of physical therapy and kinesiology at UMass Lowell. "Even though it's an intensive program where they're training the arm, you're really training the brain, not the arm," she says.

The discovery of the pulses that maintain unused motor circuits should allay some fears about using CIMT on children, Gauthier says. "Therapists have expressed concern [about] what's going to happen if you restrain that stronger arm for two weeks," she says. "Is that going to affect their normal development? And what this study shows is that it probably won't."

Dosenbach says the experiment came about because he often prescribes CIMT for young patients who have an arm that is partially paralyzed as the result of a stroke, illness, or traumatic brain injury.

"You put their good arm, their more functional arm, in a full-arm cast all the way down to their fingertips to force them to use the other side," he says.

One day a colleague pulled Dosenbach aside and said, "You know, Nico, you should do this to yourself and we should scan you to find out how the brain reorganizes in that situation."

Dosenbach agreed, and chose a pink cast because "my daughter at the time was two and I didn't want to frighten her."

Dosenbach wanted to maximize the effect on his brain so for two weeks, he kept doing all the things he'd done before, like buckling his belt.

"The first time it took 45 minutes," he says. "I didn't want to give up and ask for help, so I was late for work."

He quickly got better at these daily tasks. "The whole goal was that I wouldn't cut myself any slack, and so, yeah, I got pretty good at changing diapers with a fiberglass cast on," he says.

Every day at 5 a.m. Dosenbach went in for a brain scan.

He says those scans revealed dramatic changes in the first few days.

The brain is very stable unless it has to change," he says. "And then it can change at a rate, and at a scale, that I never would have never thought possible until [I saw] the results from the study."

The scans also showed that as circuits involved in controlling the idle arm began to fade, a new signal appeared in the brain, Dosenbach says.

"We start seeing in the disused motor circuitry these pulses of spontaneous activity that are very large that actually seem to maintain the connection," he says, adding that this would explain how people are able to regain motor skills very quickly after an injured arm or hand has healed.

And patients who receive constraint-induced therapy do improve quickly, Gauthier, says. She and her research team have measured the change by having patients play a video game that tests the performance of their less functional arm — the one that's not constrained.

"So we're able to track the trajectory of the recovery over time and we can see that a lot of the recovery happens in a very short period of time," she says.

Gauthier isn't sure whether the pulses Dosenbach discovered can help patients who've had a major stroke or severe brain injury.

"Those pulses may go through in a normal brain," she says. "But if you have a damaged brain, those pulses may not be happening, we just don't know." [Copyright 2020 NPR]