Impaired inhibition of a pre-planned response in focal hand dystonia.
The hypothesis that focal hand dystonia (FHD) is associated with impaired inhibitory function is supported by a broad base of evidence from studies of neurophysiological function. The purpose of this study was to investigate the inhibition of a pre-planned response in FHD and control subjects. Nine FHD subjects and 11 control subjects performed an anticipated response task, which required them to lift their index finger from a keyboard button to stop the sweep of an indicator at a specified point on a sweep-dial. The affected hands of the FHD subjects were tested, as were the dominant hands of the control subjects. Electromyographic (EMG) data were recorded from the long finger extensors of the tested arm. On 90 out of 220 trials, the sweep indicator would stop prior to the specified point, and subjects were instructed to continue holding the key down when this occurred. The sweep indicator stopped 10 times at each of nine different points around the dial in a randomised order. The accuracy of subjects' performance when stopping the sweep indicator at the specified point, and the proportion of 'stop' trials where they successfully inhibited this pre-planned response, were recorded. The sweep indicator stop time at which each subject had a 50% probability of successfully inhibiting their response (R50) was calculated, as was the probability of extensor EMG (burst) activity occurring during a successfully inhibited response. For FHD subjects, it was found that R50 was significantly lower, and the probability of an extensor EMG burst occurring during a successfully inhibited response was significantly higher, compared to control subjects. These results are discussed with respect to the 'horse-race' model for the inhibition of pre-planned responses.
Stinear
Cathy M
CM
Human Motor Control Laboratory, University of Auckland, Auckland, New Zealand.
Byblow
Winston D
WD
D000328:Adult; D016022:Case-Control Studies; D020821:Dystonic Disorders / Q000503:physiopathology* / Q000523:psychology*; D004576:Electromyography; D005260:Female; D005385:Fingers; D006225:Hand; D006801:Humans; D033182:Intention; D008297:Male; D008875:Middle Aged; D009068:Movement; D009433:Neural Inhibition