Proficient motor impulse control in Parkinson disease patients with impulsive and compulsive behaviors

Abstract

Background: Parkinson disease (PD) patients treated with dopamine agonist therapy can develop maladaptive reward-driven behaviors, known as impulse control disorder (ICD). In this study, we assessed if ICD patients have evidence of motor-impulsivity.

Methods: We used the stop-signal task in a cohort of patients with and without active symptoms of ICD to evaluate motor-impulsivity. Of those with PD, 12 were diagnosed with ICD symptoms (PD-ICD) and were assessed before clinical reduction of dopamine agonist medication; 12 were without symptoms of ICD [PD-control] and taking equivalent dosages of dopamine agonist. Levodopa, if present, was maintained in both settings. Groups were similar in age, duration, and severity of motor symptoms, levodopa co-therapy, and total levodopa daily dose. All were tested in the dopamine agonist medicated and acutely withdrawn (24 h) state, in a counterbalanced manner. Primary outcome measures were mean reaction time to correct go trials (go reaction time), and mean stop-signal reaction time (SSRT).

Results: ICD patients produce faster SSRT than both Healthy Controls, and PD-Controls. Faster SSRT in ICD patients is apparent in both dopamine agonist medication states. Also, we show unique dopamine medication effects on Go Reaction time (GoRT). In dopamine agonist monotherapy patients, dopamine agonist administration speeds GoRT. Conversely, in those with levodopa co-therapy, dopamine agonist administration slows.

Discussion: PD patients with active ICD symptoms are significantly faster at stopping initiated motor actions, and this is not altered by acute dopamine agonist withdrawal. In addition, the effect of dopamine agonist on GoRT is strongly influenced by the presence or absence of levodopa, even though levodopa co-therapy does not appear to influence SSRT. We discuss these findings as they pertain to the multifaceted definition of 'impulsivity,' the lack of evidence for motor-impulsivity in PD-ICD, and dopamine effects on motor-control in PD.

Keywords: Dopamine agonist; Impulse control disorder; Inhibition; Motor impulsivity; Parkinson disease; Reaction time.

Copyright © 2014 Elsevier Inc. All rights reserved.

Figures

Figure 1

a) Mean reaction times (RT) to go arrows as a function of Group. All groups showed similar mean reaction times. Error bars reflect the standard error of the mean. b) Stop signal reaction times (SSRT) as a function of Group. PD-C patients showed similar SSRTs compared to HCs, with PD-ICD patients producing faster SSRTs than both PD-C patients and HCs. Error bars reflect the standard error of the mean.

Figure 2

a) Mean reaction times (RT) to go arrows On and Off DAAg medications for PD groups (PD-C and PD-ICD). Mean reaction times were similar between groups and across medication states. Error bars reflect the standard error of the mean. b) Stop signal reaction times (SSRT) On and Off DAAg medications for PD groups (PD-C and PD-ICD). Mean SSRTs were comparable when patients were On or Off DAAg, however, the PD-ICD group showed faster SSRTs when compared to the PD-C group, independent of medication state. Error bars reflect the standard error of the mean.

Figure 3

a) Mean reaction times (RT) to go arrows as a function of Group (DAAg Monotherapy, DAAg with Levodopa cotherapy) and Medication State (on DAA, off DAA). Patients taking DAAg monotherapy showed a significant speeding of RT On compared to Off DAA medications. Patients taking both DAAg and Levodopa showed a reduction in RT when compared to task performance on Levodopa only. Error bars reflect the standard error of the mean. b) Stop signal reaction time (SSRT) as a function of Group (DAAg Monotherapy, DAAg with Levodopa cotherapy) and Medication State (on DAA, off DAA). Mean SSRT was marginally, but non-significantly, faster among patients on Levodopa cotherapy compared to those on DAAg Monotherapy, regardless of medication state. Error bars reflect standard error of the mean.