Volume 16, Number 4
Mapping Movement
Recording what's normal when you walk or reach gives a telling contrast in disease.
Many people with one-sided damage to cortical motor areas from trauma or a stroke, benign tumors or even the ultimate "damage" of a hemispherectomy can, fortunately, still walk. But they're troubled by an undeniable, unfixable limp.
Now, after paving the way for several years, Amy Bastian, Ph.D., is courting a remedy that's come from her study of the cerebellum, specifically, from a capability hard-wired in that organ. It's like finding $20 in the pocket of an old jacket.
Bastian, whose doctoral
degree is in movement science, has made it her work to deconstruct the action
of trunk and limbs in both health and disease. At the Kennedy Krieger Motion
Analysis Laboratory she directs-she's also with Hopkins' Neurology-Bastian
first tracks normal movement with an infrared camera, then uses the computer
to help save the data in a more useful form. Hollywood used similar kinematic
analysis, as it's called, to create the motion of the creepy Gollum in Lord
of the Rings. Bastian contrasts this normal movement with that typical of neurological problems like Parkinson's disease (PD), stroke and the spino-cerebellar ataxias-hereditary diseases marked by a reeling, uncoordinated gait. "We've captured what neurologists intuitively pick up about movement in cerebellar disease or PD," she says, "and quantified it."
The work is a tool for learning how specific brain damage can make movement patterns distinctively flawed. In one early study, for example, she explained why patients with cerebellar disease overreach objects, based on the body's natural balance between action and reaction. Patients' shoulders flex too much when they reach, she found. That's because the cerebellar fine-tuning that normally compensates for the elbow's reactive torque can't kick in.
Because it picks up subtle changes in movement, Bastian's approach can also track therapies. She recently compared the effect of deep brain stimulation on one or on both sides of the brain. Stimulating both sides most improves walking, she found, but one side is enough to improve arm movement.
So far, most of Bastian's work has clarified what goes wrong. "But this newest study," she says, "should let us treat a gait problem."
A limp after stroke or hemispherectomy typically stems from poor coordination of two- legged movement. It's a result, she believes, of the way the damaged cortex alters how the spinal cord and brainstem process walking information. Fortunately, she says, paths from the cerebellum to those areas probably stay intact. "And because we think that cerebellar circuits oversee learning of new motor tasks, that makes all the difference." The cerebellum, then, may be prodded to retrain coordination.
Bastian has normal controls walk a split-belt treadmill. Running one belt set three or four times faster than the other mimics the limp. "People feel pretty strange at first," she says, "but after 15 minutes, they catch on to it." When they jump off the treadmill, there's an aftereffect, a feeling that walking's different. "That shows us the brain is adapting!" What's exciting is that the hemispherectomy patients and stroke patients Bastian's had on the treadmill are also able to adapt-an important sign cerebellar learning is kicking in. "With enough of the right training," she says, "we think we can make the changes long-term."
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