Timing of tactile and visuo-tactile stimuli is impaired in patients with cervical dystonia

Psychophysical studies show alterations of cross-modal integration and timing processes in patients with generalized and focal hand dystonia. Here we assess the capability of 10 cervical dystonia patients, 5 patients with cervical pain but no dystonia, and 10 healthy controls to determine whether pairs of visual, tactile or visuo-tactile stimuli were simultaneous or sequential (TD threshold) and which stimulus preceded the other (temporal order judgement, TOJ). Visual stimuli consisted of light emitting diodes and tactile stimuli of non-noxious electrical shocks delivered to the hands. Intervals between stimuli were increased from 0 to 400 ms in steps of 10 ms. Cervical dystonia patients had a clear impairment of tactile and visuo-tactile temporal discrimination compared with patients with cervical pain but no dystonia who performed as well as healthy subjects. This suggests that deficits of temporal discrimination in cervical dystonia patients are not due to the possible distracting effect of unpleasant sensations or pain. Comparisons with previous studies show that deficits in cervical dystonia were more severe than in focal hand dystonia and less severe than in generalized dystonia. Thus, impairment of sensory timing may be a marker of disease, which varies along a continuum in the different forms of dystonia.