Velocity modulation and rhythmic synchronization of gait in Huntington's disease.

This study analyzed the ability of patients with Huntington's disease (HD) to modulate gait velocity without external sensory cues and in response to an auditory rhythmic cue within a frequency entrainment design. Uncued gait patterns of 27 patients were first assessed during normal, slower, and faster self-paced walking. During rhythmic trials, metronome and musical beat patterns were delivered at rates 10% slower and 10-20% faster than baseline cadence to cue gait patterns. After the rhythmic trials, patients were retested at normal gait speed without rhythm. Gait velocities in the patients with HD were below normal reference values in all ranges. Patients were able to significantly (p <0.05) modulate their gait velocity during self-paced and rhythmic metronome cueing but not during music. The ability to modulate gait velocity was retained regardless of the severity of the disease. Gait velocity declined with an increase in disability and chorea score. The disability score differentiated better between gait velocity of moderately and severe patients than chorea score. Slowness of gait was significantly correlated only with disability score and not with chorea. Patients had more difficulty producing adequate step rates than stride lengths during normal and fast walking speeds. After the rhythmic trials, unpaced gait velocity remained significantly (p <0.05) higher than baseline. This carry-over effect was not seen after the uncued trials. Synchronization ability was deficient in all patients, deteriorated with severity of disease, and was already compromised in patients with soft disease signs. Rhythmic tracking of music declined more with severity of disease than metronome tracking. In summary, patients were able to modulate velocity with and without external cues. Velocity adaptations to the external rhythm in music and metronome were achieved without exact synchronization between step cadence and rhythmic stimulus.

Motor learning by imagery is differentially affected in Parkinson's and Huntington's diseases.

Studies of motor imagery and motor learning have thus far been concerned only with its effects on healthy subjects. Therefore, in order to investigate the possible involvement of the basal ganglia, the effectiveness of motor imagery in the acquisition of motor constants in a graphomotor trajectorial learning task was examined in 11 non-demented mildly affected Huntington's disease (HD) patients and 12 non-demented Parkinson's disease (PD) patients. The patients received, after baseline, 10 min of motor imagery training, followed by a motor practice phase. Additionally, a test battery for visual imagery abilities was administered in order to investigate possible relations between visual and motor imagery. The results showed that imagery training alone enabled the HD patients to achieve a significant approach to movement isochrony, whereas the PD patients showed no marked improvements, either with motor imagery or with motor practice. Furthermore, the PD patients had more difficulties than the HD patients in solving the visual imagery tasks. Subsequent correlational analysis revealed significant relationships between the degree of caudate atrophy in the HD patients and their performance in the visual imagery tasks. However, there were no substantial correlations between the performance on the visual imagery tasks and the improvement of motor performance through motor imagery, which indicates that visual and motor imagery are independent processes. It is suggested that the dopaminergic input to the basal ganglia plays an important role in the translation of motor representations into motor performance, whereas the caudate nucleus atrophy of the HD patients does not seem to affect motor imagery, but only the visual imagery process. Furthermore, the deficits found in PD patients might also be related to their limited attentional resources and difficulties in employing predictive motor strategies.