Exactly what triggers dystonia — an involuntary muscle contraction of the hand, fingers, neck or mouth, which is sometimes very painful — is unclear. But some researchers think the underlying problem that causes it may also be the key to treating it, and other brain-linked disorders like Parkinson's.

Guitarist Jamie Shear

Ajax, Ont. guitarist Jamie Shear suffers from dystonia, a movement disorder that is more common among musicians than any other professional group. (Facebook)

Ajax, Ont. professional musician Jamie Shear explained how he first noticed his own dystonia.

"Picked up the guitar. Couldn't hold the pick the way I wanted to," he said. "So I went to see a doctor."

Shear's doctor is Robert Chen, a dystonia specialist at Toronto Western Hospital. Chen diagnosed Jamie with "focal dystonia," a type of involuntary contraction involving just one or a few muscles.

The Dystonia Medical Research Foundation says the disorder affects 300,000 people in the U.S. and Canada. According to the U.K.-based Dystonia Society, it can affect members of any profession which requires repeated movements — like writers, athletes or craftspeople — but is more common among musicians than any other professional group.

The underlying problem in all cases is normal brain plasticity — the brain's ability to form new connections between neurons through experience — gone rogue.

"Say someone would keep practicing a musical instrument," said Chen. "You want to induce a good type of plasticity, to learn how to play maybe a very difficult sequence. But in some cases this can go wrong and lead to an unfavourable or abnormal type of motor program."

Muscle function is initiated by the motor cortex, straddling the top of your brain. Towards the bottom, the basal ganglia make motions smooth. Right behind, the cerebellum acts as an autopilot, monitoring your body position on the fly, calculating how best to move when the motor cortex says "go."

"Traditionally, we think that dystonia is mainly a disturbance of the basal ganglia," said Chen. "Patients with a stroke in the basal ganglia will often develop dystonia. But in the last, I'd say, five to 10 years, there is lots more evidence that the cerebellum is also involved."

'Tangled networks' lead to disorder

Philippe Isope, of France's Institute of Cellular and Integrative Neurosciences, studies the cerebellum in his lab in Strasbourg, France. ​He explains that neuronal circuits are like a highway system that constantly monitors and adjusts itself — plastically.

"Imagine that you have a big mesh of highway," Isope said. "If the action is okay, there is a mechanism that will say, 'That was a good road.' Communication points between two cells — between two neurons — will be strengthened by the fact that the action is well done."

Sometimes, though, networks get tangled up, and muscles stiffen. The result is Shear's fingers lifting away from his guitar pick, for example, or a person with torticollis — excruciating neck spasms.

Dystonia can also affect the eyes, eyelids, mouth, tongue and rectum.

"This problem is a communication breakdown," said Isope. 

The solution may be to use the brain's plasticity to stop the rogue neural loop, and restore the good one.

Teaching the brain new patterns

"Basically, what you do is to provoke new plasticity in the network, and then the network can learn again the correct pattern, in a sense."

Back in Ajax, Shear's dystonia has not gone away. Researchers are studying ways to help brain circuits get over their hiccups.

"I have gone and volunteered for different areas of experimentation, where they've created headaches for me," he said. "But enough for them to do research and give me free Botox at the same time."

Botox injections weaken the tiny muscles that make Jamie's digits lift from his pick. His cerebellum should respond by backing off these muscles, and assigning others in their place. The same approach may work for the tens of thousands of other Canadians with focal dystonia.

Having learned how to replace hiccupping neural circuits in people with dystonia, the next step could be to restore motor function in stroke patients, for example — where some circuits have died, but others can be recruited; or getting Parkinson's patients to sing in choirs, thereby restoring facial expression.

How best to promote brain plasticity in different clinical situations is the big question.

The research goes on.