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Nonlinear sensory cortex response to simultaneous tactile stimuli in writer's cramp

Authors

  • Terence D. Sanger MD, PhD,

    1. Department of Child Neurology, Stanford University Medical Center, Stanford, California USA
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  • Alvaro Pascual-Leone MD, PhD,

    Corresponding author
    1. Behavioral Neurology Unit and Movement Disorders Center, Department of Neurology, Beth Israel Deaconess Medical Center, Boston, Massachusetts USA
    • Behavioral Neurology Unit, Beth Israel Deaconess Medical Center, 330 Brookline Avenue, Boston, MA 02215

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  • Daniel Tarsy MD,

    1. Behavioral Neurology Unit and Movement Disorders Center, Department of Neurology, Beth Israel Deaconess Medical Center, Boston, Massachusetts USA
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  • Gottfried Schlaug MD, PhD

    1. Neuroimaging Laboratory, Department of Neurology, Beth Israel Deaconess Medical Center, Boston, Massachusetts USA
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Abstract

Writer's cramp is a task-specific dystonia that leads to involuntary hand postures during writing. Abnormalities of sensory processing may play a pathophysiological role in this disorder. Electrophysiology studies in a monkey model of focal dystonia have revealed de-differentiation of sensory maps and the existence of single cells in hand regions of area 3b with enlarged receptive fields that extend to the surfaces of more than one digit. These changes may lead to abnormal processing of simultaneous sensory inputs. To study abnormal processing of simultaneous sensory information in adult humans with writer's cramp, we used functional magnetic resonance imaging to compare the response in primary sensory cortex with simultaneous tactile stimulation of the index and middle finger, with the response to stimulation of each finger alone. We tested five patients with writer's cramp and seven unaffected (normal) subjects. In the normal subjects, a linear combination of the activation patterns for individual finger stimulation predicts the pattern of activity for combined stimulation with 12% error. In writer's cramp patients, the linear combination predicted the combined stimulation pattern with 30% error. Results indicate a nonlinear interaction between the sensory cortical response to individual finger stimulation in writer's cramp. This altered interaction may contribute to the motor abnormalities. © 2001 Movement Disorder Society

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