Choice reaction time after levodopa challenge in parkinsonian patients
Introduction
Studies of motor function provide useful information on quality of life and efficacy of anti-parkinsonian drug therapy in parkinsonian subjects. Testing patients being off medication is essential to get further informations on the pathophysiology of the disease and the mechanisms underlying Parkinson’s disease (PD) and basal ganglia function [1]. Thus it would make sense, that long-term application of a specific medication has no positive or negative effect on the studied task or paradigm [1]. It is generally accepted, that parkinsonian patients have deficits in the preparation and execution of movements [2], [3], [4], [5], [6], [7], [8]. Various trials on movement control and preparation, using different types of reaction time paradigms, provided a considerable amount of information in the past years with controversial results [7], [8], [9]. Crucial issues are (i) impact of PD itself on motor behaviour and (ii) influence of long-term application of various dopaminergic drugs on stimulus identification and response programming [7], [8], [9]. All these previous trials enrolled parkinsonian individuals (i) in the medicated state, (ii) being off medication for at least 12 h as generally agreed reasonable compromise, or (iii) being previously untreated, which is also termed “de-novo” [5], [6], [7], [8], [10]. Sometimes these studies did not even differentiate between these various types of patients and no trial considered the acute effects of application of dopaminergic drugs [7], [8], [9].
Objective of this study was to determine the effect of long-term dopaminergic substitution therapy within a standardized levodopa challenge test design in combination with a repeatedly performed choice reaction time task in parkinsonian individuals.
Section snippets
Subjects
Group 1 consisted of 17 previously untreated, right-handed idiopathic parkinsonian individuals (female n=6, male=11). Group 2 included 14 right-handed idiopathic parkinsonian patients (female n=1, male=13). They were off medication for at least 12 h at the time of examination and task performance [10] (Table 1). All hospitalized participants received the same kind of hospital food, no low protein diet. All parkinsonian participants responded to dopaminergic treatment. They fulfilled clinical
Results
UPDRS II (P=0.003) and UPDRS III (P=0.02) differed between treated and previously untreated parkinsonian subjects in contrast to age (P=0.07), HYS range (P=0.97), UPDRS I (P=0.24) and BDI score (P=0.56), RT (P=0.99) and MT (P=0.09) at timepoint 0 (Table 1).
A significant trend for a delayed RT in untreated (P=0.04) but not in treated (P=0.22) parkinsonian patients appeared compared to controls. MT was significant (P=0.012) longer in treated parkinsonian participants compared to controls,
Discussion
To date, comparisons of RT and MT of parkinsonian subjects with controls showed controversial results regarding initiation and execution of movement in various choice reaction time paradigms for the evaluation of cognitive slowing in PD [3], [4], [7], [8], [20]. Previously, when patients were without dopaminergic substitution, within-subject-comparisons predominantly showed a slower performance of the choice reaction time task. In these trials parkinsonian subjects were first off- and then
Acknowledgements
We thank S. Marchewitz and U. Claußnitzer for technical assistance.
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