External cueing improves temporal characteristics of motor imagery in patients with Parkinson's disease

Abstract

Objective: To evaluate the effect of external cues on motor imagery (MI) of upper limb movements in patients with Parkinson’s disease. Background: MI is a well known training technique among athletes and has recently gained attention as a promising practice method for neurological patients. In patients with PD, however, impairments in MI ability were reported, limiting the implementation and potential benefits of MI practice in these patients’ rehabilitation. Therefore, we investigated whether the MI quality of patients with PD could be increased by means of external cueing. Methods: 14 non-demented patients (MMSE  24) in mid and early stage of the disease (H&Y 1-3), who were “on” medication, and 14 age-matched controls physically executed and visually imagined two tasks: 1) cyclical goal-directed aiming at a fixed speed of 0.5Hz, performed as accurate as possible, and 2) transportation of blocks (box- and block test), performed at maximum speed. These tasks were carried out in the presence and absence of visual and auditory cues. Visual analogue scales were used to assess imagery vividness, and mental chronometry and eye movement recording to objectively evaluate the temporal characteristics of MI in comparison to physical execution. Data were analysed by means of repeated measures ANOVA’s (=0.05). Results: The presence of visual cues significantly improved the participants’ imagery vividness and led to a higher consistency in imagery duration over trials and a higher temporal isochrony with physical execution. The PD patients were slower than the controls in all conditions, but the presence of visual cues significantly reduced their bradykinesia during imagery. This was confirmed by the eye movement data, showing lower eye movement times and a higher eye movement frequency during imagery if visual cues were provided. Conclusions: The provision of visual cues improves the vividness and temporal structure of motor imagery in patients with PD. Since cueing can be used to diminish PD patients’ bradykinesia during imagery, we hypothesise that it can increase the efficacy of motor imagery practice in PD rehabilitation.