Exteroceptive and interoceptive stimuli in dystonia.

Some patients with torsion dystonia experience a dramatic increase or decrease in symptoms when performing specific activities. The activities that influence dystonic symptoms vary from person to person. An activity or sensory stimulus that reduces symptoms has been called a "sensory trick" or, in cervical dystonia, a "geste antagoniste." When a single activity induces symptoms of dystonia, the dystonia is called "task specific." We have discovered that in some patients, thinking about a sensory trick or task affects the dystonia in the same way as actually performing the activity. We present three representative patients, and discuss the relevance of this observation to the understanding of dystonia.