Horovitz and her colleagues are interested in understanding writer’s cramp (which Dr. Mark Hallett, chief of the branch, says is considered a rare disease) and in using the ailment to probe deeper questions about how humans perform specific motor tasks.
Writer’s cramp, a painless condition, is technically known as a type of focal hand dystonia (FHD) and is characterized by abnormal posture or movement. The focal dystonias typically start with a single task, but may spread to other tasks and may even eventually afflict limbs that are at rest, said Horovitz.
Two studies under way in Hallett’s lab focus on right-hand FHD and involve both patients and normal controls, whose study results, when compared, help identify the brain networks involved when writing with the dominant hand.
Put simply, Horovitz and her colleagues are having study subjects complete simple tasks—writing, zig-zagging and tapping—with both their right and left hands, and also their right feet, then watching which areas in the brain show heightened activity.
“We want to know what areas in the brain map exclusively to writing,” Horovitz explained.
As one might guess, writing was found to be more complex than zig-zagging or tapping, with the strongest difference in brainpower originating in the left putamen, but also in the supplementary motor area, Exner’s area (Sigmund Exner, a Vienna-born physiologist, tied handwriting to a brain locale above Broca’s area in a paper published in 1881, with Conrad Eckhard) and the supramarginal gyrus.
Further, subjects with writer’s cramp had deficiencies of putamen activation and connectivity and deficits in functional connections to Exner’s area, said Horovitz.
She and her colleagues are finding that handwriting, and likely any other task-specific activity, “requires more than a simple combination of effector (motor execution) and task.”
Investigators in the human motor control section are also conducting imaging studies to determine if there is a difference between writer’s cramp and musician’s cramp. In 2004, Hallett’s lab was resoundingly credited with restoring to piano virtuoso Leon Fleisher the ability to use two hands at the keyboard. In gratitude for a therapy involving injections of botulinum toxin to free cramped muscles in his hand, Fleisher gave a free SRO performance in Masur Auditorium.
During a brief Q&A session, Hallett noted that writer’s cramp is, for reasons unknown, the most common focal dystonia in India, and that texting (no surprise to the parents of teenagers), and any other repetitive activity, can result in focal dystonia. He said that typing can offer relief to those afflicted with writer’s cramp and that the ailment is associated with a higher frequency of obsessive compulsive symptoms.
And sadly, you can’t just give your hand a rest when writer’s cramp shows up; it will return the next time you attempt to write, he said.