Temporal discrimination of cross-modal and unimodal stimuli in generalized dystonia

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Abstract
Background: Motor and nonmotor timing functions and cross-modal processing of visual–tactile signals may be linked to basal ganglia. These neural structures are thought to be dysfunctional in dystonia. Objective: To test whether cross-modal stimulation influences deficits of temporal discrimination in dystonia. Methods: Eight patients with generalized dystonia and 10 control subjects were asked to discriminate whether pairs of unimodal (tactile or visual) and cross-modal (visual and tactile) stimuli were simultaneous or sequential and, in the latter case, which stimulus preceded the other. Visual stimuli consisted of red lights and tactile stimuli of non-noxious electrical shocks. Intervals between stimuli in each pair were increased from 0 to 400 msec (in steps of 10 msec). Results: Patients with dystonia recognized the asynchrony between the experimental stimuli and judged correctly which stimulus in a pair came first, at significantly longer intervals than did controls. Moreover, differences in performance between patients and controls were maximal for cross-modal stimuli. The defective performance of patients with dystonia in the cross-modal combinations showed a high positive correlation with the severity of symptoms. Conclusion: Patients with generalized dystonia present with difficulties both in timing functions and in cross-modal processing of visual–tactile stimuli.