Objective: We wanted to assess whether i) Parkinson’s disease (PD) patients at Hoehn and Yahr (HY) stage 1 show a global or a selective impairment in inhibitory control; and whether ii) left-dominant PD (LPD) patients have a greater deficit in inhibiting a pending action than right-dominant PD (RPD) patients.

Background: It is well known that PD patients suffer from a deficit in inhibitory control [1,2], however this is not a unitary construct and it is unclear whether Parkinson’s patients at early stage of the disease (HY1) exhibit a deficit in outright stopping (reactive inhibition), a deficit in the ability to shape their motor strategy in anticipation of known task demands (proactive inhibition), or both. In addition, as it has been suggested that inhibition relies upon a right-lateralized pathway, we tested whether LPD patients suffered from a more severe deficit in this key executive function than RPD patients.

Method: Via a reaching stop signal task [1,3,4,5], we assessed both proactive and reactive inhibition in 15 LPD, 15 RPD patients, and in 23 healthy subjects.

Results: We found that reactive inhibition was more impaired in PD patients than in healthy subjects. However, proactive inhibition [4,5] was not affected. Furthermore, we did found no differences between LPD and RPD patients. Importantly, we confirmed these negative findings using not only inferential statistics, but also the Bayesian statistic [6].

Conclusion: For the very first time, we found evidence for a deficit of reactive inhibition in the earliest stages of PD in the absence of evidence for deficits in proactive inhibition. These findings have clinical relevance as they provide key insights on the time-course of the disease. In addition, we confirmed on a different population of PD patients our previous results [4,5] showing that the onset of the disease does not affect inhibition.

References: [1] Mirabella G, Fragola M, Giannini G, Modugno N, Lakens D. Inhibitory control is not lateralized in Parkinson’s patients. Neuropsychologia 2017;102:177–189. [2] Gauggel S, Rieger M, Feghoff TA. Inhibition of ongoing responses in patients with Parkinson’s disease. J Neurol Neurosurg Psychiatry 2004;75(4):539–544. [3] Mirabella G, Iaconelli S, Romanelli P, et al. Deep brain stimulation of subthalamic nuclei affects arm response inhibition in Parkinson’s patients. Cereb Cortex 2012;22(5):1124–1132. [4] Mirabella G, Iaconelli S, Modugno N, Giannini G, Lena F, Cantore G. Stimulation of subthalamic nuclei restores a near normal planning strategy in Parkinson’s patients. PLoS ONE 2013;8(5): e62793. [5] Mancini C, Modugno N, Santilli M, et al. Unilateral stimulation of subthalamic nucleus does not affect inhibitory control. Front Neurol 2018;9:1149. [6] Rouder JN, Speckman PL, Sun D, Morey RD, Iverson G. Bayesian t tests for accepting and rejecting the null hypothesis. Psychon Bull Rev 2009;16(2):225–237.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/parkinsons-disease-patients-at-hoehn-and-yahr-stage-1-show-deficits-in-reactive-but-not-proactive-inhibitory-control/