Cognitive Daily

There was a fascinating article in the Washington Post last May about Dilbert creator Scott Adams’ battle with focal dystonia. Though the symptoms of this disorder are involuntary muscle contractions (in Adams’ case, his right pinky finger), the root of the problem is in the brain. For Adams, it has meant suspending his cartooning career more than once. The first time, he taught himself to draw with his left hand, only to see the symptoms reappear there. He’s also tried grueling physical therapy regimens. His most recent effort to battle dystonia has been drawing his cartoons using a computer graphics tablet.

So what’s different about brains with focal dystonia? Neuroimaging has found that the basal ganglia is the affected area of the brain — not surprisingly, this is the area responsible for motor control. People suffering from focal dystonia are also limited in their ability to plan and execute muscle movements. So though the most common form of focal hand dystonia is simply called “writer’s cramp,” clearly there’s much more going on here.

If focal dystonia affects not only our ability to control muscles, but also planning muscle movement, maybe it affects how we think about movement as well. Remember, we’ve discussed how memory for visual images appears to make use of the visual system. Perhaps thinking about moving body parts also relies on the basal ganglia. In a pioneering experiment in 1971, Roger Shepard and Jacqueline Metzler found that when people try to determine if two objects are the same, the time the decision takes corresponds to how far the objects are rotated. If one object is rotated, say 90 degrees compared to the other, then the comparison takes less time than if the object is rotated by 180 degrees. They concluded that people must mentally rotate the objects in order to make the comparison.

Mirta Fiorio, Michele Tinazzi, and Salvatore Aglioti realized that they could apply Shepard and Metzler’s method to people with focal dystonia. Perhaps focal dystonia also affects the rate of mental rotation. But Fiorio’s team took this analysis one step further: is it possible, since focal dystonia only affects certain regions of the body, that mental rotation is only impaired for those body parts? They worked with 15 people who suffered from writer’s cramp in their right hands, and 15 normal individuals.

Participants sat at a computer screen with their own hands hidden from view. A photo of a hand or a foot appeared on the screen, and viewers responded “right” or “left” by speaking into a microphone. The body parts were displayed in standard (0-degree) orientation, and also rotated in 60-degree increments. Here are the results:

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Participants with hand cramps mentally rotated photos of hands more slowly than normal participants. It appears that focal dystonia has an impact not only on muscle movement, but also thinking about moving body parts. But now look at the data for rotating feet:

i-e66f133ed308b2d8560f51f0a06a1d0d-dystoniafoot.gif

Though there is a trend towards rotating feet more slowly as well, this result failed to achieve statistical significance. So focal dystonia really appears to affect thinking only on the specific muscle groups affected by the condition. Interestingly, however, even though these patients only showed symptoms of focal dystonia on their right hands, they were slower at mental rotations for both hands. Fiorio et al. argue that this may suggest that focal dystonia actually affects the mental representation of hands in general, not the particular afflicted hand.

Many focal dystonia patients — including Scott Adams — train themselves to use their opposite hand, only to find the symptoms recurring in the new hand a few years later. Adams’ current practice of using a large digital tablet may be less vulnerable to this problem, since he is using the larger muscle groups of his arm to draw with, instead of his hand. Dilbert fans the world over certainly must hope this is the case!

Fiorio, M., Tinazzi, M., & Aglioti, S.M. (2006). Selective impairment of hand mental rotation in patients with focal hand dystonia. Brain, 129, 47-54.

Comments

  1. #1 Jen
    January 12, 2006

    But those with writer’s cramp were slower even at 0 degrees rotation. Doesn’t that hurt the mental rotation theory and suggest something else? Or was the difference at 0 degrees not significant?

  2. #2 Dave Munger
    January 13, 2006

    Jen–

    Good question. The difference at 0 degrees was not significant in the “foot” condition, but it was significant for the “hand” condition. But also notice that reaction time was not zero for either group — it took 1100 milliseconds for the normal group to respond at 0 degrees. So other mental processing besides rotation is necessary for people to respond — those abilities are apparently also partially impaired for people with focal dystonia.

    The key here is that there are larger differences for larger rotations, and that those differences are significant — thus mental rotation is clearly impaired for people with focal dystonia, but only when they mentally rotate images of the affected body part.

  3. #3 Monado
    January 31, 2006

    Maybe focal dystonia makes it slower to set up the image of a poised hand before starting mental rotation.

  4. #4 Wanda Freeman
    May 28, 2007

    I was diagnosed with Bells Palsy in 2001. My face is still paralyzed on the right side. At first my right eye would not close, so it had to be taped down. Then a year or so later, it wouldn’t stay open. Now I use a lid lifter to try to raise to some. My right eyebrow will not raise at all,nor will my smile work on the right.
    Could this be related?+++++

  5. #5 Dave Munger
    May 28, 2007

    Wanda, I’m not a neurologist, but I think your situation is different from Scott Adams. Your symptoms always occur on the same side of your face, but Adams has had symptoms on both sides of his body. That suggests your condition is localized to one hemisphere, while his is not.

    That said, it’s still possible that you might be slower to think about activities in the affected parts of your body, so in that sense they might be related — this study just doesn’t address your situation.

  6. #6 Jane Snyder
    January 11, 2009

    Hi,
    I have been diagnosed with Focal Leg Dystonia. Do you know anything about Focal Leg Dystonia?
    Thanks you, Jane Snyder

  7. #7 Poonam
    July 8, 2009

    I’ve just been diagnosed with focal task specific right leg dystonia. I would like to learn more about it and talk with others who are like me.