title: Levodopa medication does not influence motor inhibition or conflict resolution in a conditional stop-signal task in Parkinson's disease.
abstract: Evidence from animal, clinical, and imaging studies suggests that the basal ganglia and their frontal connections mediate motor inhibition, but the role of dopamine remains unclear. The aim of our study was to investigate, for the first time, whether levodopa medication influences motor inhibition and conflict resolution on the conditional stop-signal reaction time task in patients with Parkinson's disease (PD) tested on or off their medication. Sixteen PD patients and 17 healthy controls performed the conditional stop-signal reaction time (SSRT) task, which requires inhibition of responses when a stop signal is presented on "critical" trials. Additionally, on "non-critical" trials, participants are instructed to ignore the stop signal and respond, thus generating conflict between motor inhibition and initiation; and conflict-induced slowing (CIS) on these "non-critical" trials. Levodopa medication did not significantly influence response initiation, inhibition (SSRT) or the measure of conflict resolution (CIS). Compared to healthy controls, PD patients showed significantly worse response initiation and inhibition both on and off their levodopa medication. Our results suggest that motor inhibition or conflict-induced slowing on the conditional stop-signal RT task are not altered by dopamine replacement in PD. This conclusion is consistent with evidence from animal studies and clinical pharmacological investigations suggesting a role for noradrenaline in motor inhibition and impulsivity.
authors.affiliation: Cognitive-Motor Neuroscience Group, Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology and The National Hospital for Neurology and Neurosurgery, University College London, 33 Queen Square, London, UK.
authors.forename: Ignacio
authors.initials: I
authors.lastname: Obeso
authors.forename: Leonora
authors.initials: L
authors.lastname: Wilkinson
authors.forename: Marjan
authors.initials: M
authors.lastname: Jahanshahi
mesh_terms: D000368:Aged; D000978:Antiparkinson Agents / Q000494:pharmacology / Q000627:therapeutic use; D003072:Cognition Disorders / Q000188:drug therapy* / Q000209:etiology / Q000503:physiopathology*; D004185:Disability Evaluation; D056344:Executive Function / Q000187:drug effects* / Q000502:physiology; D005260:Female; D006801:Humans; D007980:Levodopa / Q000494:pharmacology / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D009433:Neural Inhibition / Q000187:drug effects* / Q000502:physiology; D010300:Parkinson Disease / Q000150:complications / Q000188:drug therapy* / Q000523:psychology*
chemical_list: D000978:Antiparkinson Agents; D007980:Levodopa