Inter-limb coupling during diadochokinesis in Parkinson's and Huntington's disease.

Patients with neurodegenerative diseases often exhibit deficits in bimanual coordination. One characteristic of bimanual movements is inter-limb coupling. It is the property of motor performance harmonization between hands during a bimanual task. The objective of this study was to identify whether spatial and temporal inter-limb coupling occurred in Parkinson's disease (PD) and Huntington's disease (HD) patients. Twenty-three PD patients and 15 healthy controls were tested. Data from 12 choreic HD patients were also taken from a databank. Participants were asked to perform a unimanual and bimanual rapid repetitive diadochokinesis task. The difference between hands in mean amplitude and mean duration of cycles was computed in the unimanual and bimanual tasks for each group. Results show that healthy controls exhibited temporal and spatial inter-limb coupling during the bimanual diadochokinesis task. Conversely, PD and HD patients exhibited temporal inter-limb coupling; but failed to exhibit spatial inter-limb coupling during the bimanual diadochokinesis task. Furthermore, HD patients exhibited reduced levels of structural coupling compared to controls and PD patients. These results suggest that alterations in basal ganglia-thalamo-cortical networks due to PD and HD do not affect temporal inter-limb coupling. However, common pathophysiological changes related to PD and HD may cause altered spatial inter-limb coupling during a rapid repetitive bimanual diadochokinesis task.