Abnormalities of motor timing in Huntington's disease.

The ability of patients with Huntington's disease (HD) and control subjects to produce rhythmic finger tapping movements at target frequencies (1-5 Hz) signalled by auditory cues, and to sustain the tapping tempo following sudden withdrawal of cues, was investigated. HD performance, in both the presence and absence of cues, was characterised by, (i) marked irregularity of instantaneous tapping rates and (ii) a tendency to tap too slowly at higher (3-5 Hz) frequency targets and too rapidly at low target frequencies. Analysis of the variability of inter-tap intervals, during uncued tapping at a target rate of 1.8 Hz, using Wing and Kristofferson's model of motor timing (Wing AM, Kristofferson AB. Percept. Psychophys. 1973; 14: 5-12), indicated disturbances of both hypothetical 'clock' and 'motor implementation' systems in HD.