Deficits of temporal discrimination in dystonia are independent from the spatial distance between the loci of tactile stimulation

To assess whether spatial variables influence deficits of temporal somesthetic discrimination in dystonic patients, 10 patients with idiopathic dystonia and 12 healthy controls were tested with pairs of non-noxious electrical stimuli separated by different time intervals. Stimuli were delivered: (1) to the pad of the index finger (same-point condition), (2) to the pad and to the base of the index finger (same-finger condition), and (3) to the pad of the index and ring fingers (different-finger condition). Subjects were asked to report whether they perceived single or double stimuli in the first condition and synchronous or asynchronous stimuli in the second and third conditions. Somesthetic temporal discrimination thresholds (STDTs) were obtained by computing the shortest time interval at which stimuli, applied to the left or the right hand, were perceived as separate in the first condition or asynchronous in the second and third conditions. STDTs were significantly higher in dystonic patients than controls in all three conditions. In both dystonia patients and controls, STDTs resulted highest in conditions whereby stimuli were maximally separated in space. Results extend cut-rent knowledge of deficits of somesthetic temporal discrimination in dystonia by showing that temporal deficits are not influenced by spatial variables.