The effects of auditory startle and nonstartle stimuli on step initiation in Parkinson's disease.

ABSTRACT

BACKGROUND: Auditory external cues enhance step initiation in Parkinson's disease (PD) patients. We wanted to explore whether a startle reaction has a comparable effect on step initiation in PD. METHODS: Thirteen PD patients and 13 aged-matched controls participated in this study. Electromyography pattern and onset toe-off time during a step initiation task were recorded in response to three different stimuli a visual imperative stimulus; visual stimulus simultaneous with a nonstartle auditory stimulus and with a startle auditory stimulus. RESULTS: In all subjects, onset of tibialis anterior was faster in the startle auditory condition, compared with the nonstartle auditory condition. However, in the patient group, there was no difference in onset of soleus and toe-off between the startle and nonstartle conditions. CONCLUSIONS: Startle reaction in PD patients demonstrates a disordered coupling between the anticipatory postural adjustments that initiate the weight shift and the movement to initiate toe-off during step initiation.