EFFECTS OF A STARTLING ACOUSTIC STIMULUS ON REACTION-TIME IN DIFFERENT PARKINSONIAN SYNDROMES

Background: The functional assessment of the startle circuit is usuall y done by analyzing the acoustic startle response (ASR). However, a st artling acoustic stimulus (SAS) also induces changes in the excitabili ty of neural structures that can be demonstrated by studying the SAS-i nduced change in the behavior of certain neurophysiologic responses. O bjective: To examine the effects induced by an SAS on voluntary reacti on time in patients with parkinsonian syndromes (StartReact effect) an d to compare the results with those obtained in a group of age-matched healthy volunteers. Methods: Twelve patients with idiopathic PD (IPD) , seven patients with progressive supranuclear palsy (PSP), seven pati ents with multisystem atrophy (MSA), and seven healthy age-matched con trol volunteers performed a simple visual reaction time task, and rece ived SAS together with the ''go'' signal in random trials. Results: Ba seline reaction time was significantly slower in PSP patients than in control subjects and MSA patients. The SAS induced a significant short ening of the reaction time in control subjects and in patients with IP D and MSA, but not in patients with PSP. The percentage of reaction ti me shortening with regard to the baseline values also differed signifi cantly between PSP patients and the other groups of subjects. The Star tReact effect was consistent throughout the experiment and showed redu ced habituation with repeated testing. Conclusions: The results are co nsistent with an abnormal function of the startle circuit in patients with PSP and agree with previous studies using the ASR. The reduced ha bituation of the StartReact effect favors its clinical applicability i n the assessment of differences between patients with parkinsonian syn dromes.