Dystonia

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Special Series: Brain Waves

Rogue Circuits

By David Kattenburg

In a crowded Tim Horton’s in Ajax, Ontario, professional guitarist Jamie Shear describes how his bout of dystonia began.

“Picked up the guitar,” Shear says matter of factly. “Couldn’t hold the pick the way I wanted to. So, I went to see a doctor.”

Dr. Robert Chen (David Kattenburg)

Dr. Robert Chen (David Kattenburg)

Jamie’s doctor was Robert Chen – a movement disorder specialist at Toronto Western Hospital. Chen diagnosed Jamie with focal dystonia, a type of involuntary contraction involving just one or a few muscles in the hand, fingers, neck or mouth, sometimes very painful.

Up to twenty percent of working musicians get struck by focal dystonia at some point. So do writers, athletes, craftspeople … an estimated 300,000 North Americans. What triggers dystonia is unclear, but the underlying problem — normal brain plasticity gone awry — may be the key to treating it and other brain-linked disorders like Parkinson’s.

 

Muscle function is initiated by the primary motor cortex, straddling the top of your brain. Towards the bottom, the basal ganglia make motion 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! Sometimes this goes wrong.

“So, say, someone would keep practicing a musical instrument; you want to induce a good type of plasticity, to learn how to play maybe a very difficult sequence,” says Robert Chen. “But in some cases this can go wrong and lead to an unfavorable or abnormal type of motor program.”

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Philippe Isope and his cerebellum slice setup

Neuronal circuits are like a highway system that constantly monitors and adjusts itself — plastically, explains Philippe Isope, a cerebellum researcher in Strasbourg, France. Isope sticks tiny electrodes into the Purkinje cells that form electrical circuits.

“Imagine that you have a big mesh of highway,” says Isope, sitting in his office on a sprawling Strasbourg campus. “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.”

Jamie Shear in action

Jamie Shear in action

But sometimes networks get tangled up in blue, and muscles stiffen. Jamie Shear’s fingers lifting away from his guitar pick, for example, or a person with torticollis – excruciating neck spasm. Dystonia also affects the eyes, eyelids, mouth, tongue … and rectum.

“This problem is a communication breakdown; a bad calculation in a relatively normal network,” says Isope. The solution? Stop the rogue neural loop; restore the good one. Your brain is plastic. You can do it.

“So 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,” Isope explains.

DSC_0741-001Back at his home in Ajax, Jamie Shear demonstrates neural plasticity in action. His dystonia has not gone away, but he’s learning to overcome unwanted muscle spasm. And he’s participating in experiments using Botox, which weakens the tiny muscles that make Jamie’s digits lift from his pick. In theory, his cerebellum should respond by backing off these muscles, assigning others in their place.

Having learned how to replace hiccupping neural circuits in people with dystonia, the next step will 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. Research goes on.

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