Objective: To determine whether predominant motor subtypes of Parkinson’s disease (PD) differentially impact distinct forms of inhibitory motor control.

Background: Parkinson’s disease (PD) impairs rapid inhibitory motor control, including split-second inhibition of reflexive, unintentional motor impulses as well as rapid inhibition of actions initiated intentionally. We hypothesized that these changes in inhibitory control processes are differentially expressed depending on the predominant PD motor symptom. Given that PD patients with predominant akinetic-rigid (AR) and postural instability/gait disorder (PIGD) experience more pronounced dyscontrol of volitional movements compared to tremor dominant (TD) patients, we predicted that AR and PIGD subtypes would show exacerbated deficits inhibiting actions.

Methods: 78 individuals with mid-stage PD (mean age: 62.96 years, mean time since symptom onset: 10.53 years, mean UPDRS III off: 38.87) were subdivided into TD, AR, and PIGD subgroups. They along with 19 healthy controls performed tasks measuring inhibition of action impulses (Simon task) and inhibition of already initiated actions (stop-signal task).

Results: PD subgroups shared similar disease/demographic characteristics. Consistent with prior studies, relative to healthy controls, PD patients showed global deficits in their ability to inhibit incorrect motor impulses as well as inhibit intentionally initiated actions. These two forms of inhibitory control were uncorrelated, confirming prior work showing that these control systems are dissociable. Most importantly, inhibitory control deficits did not differ among PD subgroups, and confidence in this null subgroup effect was confirmed using Bayes’ factor statistics.

Conclusions: Deficits in the proficiency of inhibiting actions, whether triggered impulsively or initiated intentionally, are general and distinct effects of Parkinson’s disease that do not appear to be differentially expressed in PD motor symptom subtypes.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/parkinsons-disease-motor-subtypes-show-similar-deficits-in-inhibitory-control/