Corticospinal Suppression Underlying Intact Movement Preparation Fades in Parkinson's Disease

Emmanuelle Wilhelm, Caroline Quoilin, Gerard Derosiere, Susana Paço, Anne Jeanjean, Julie Duque

Research output: Contribution to journalArticlepeer-review

Abstract

Abstract
Background
In Parkinson's disease (PD), neurophysiological abnormalities within the primary motor cortex (M1) have been shown to contribute to bradykinesia, but exact modalities are still uncertain. We propose that such motor slowness could involve alterations in mechanisms underlying movement preparation, especially the suppression of corticospinal excitability—called “preparatory suppression”—which is considered to propel movement execution by increasing motor neural gain in healthy individuals.

Methods
On two consecutive days, 29 PD patients (on and off medication) and 29 matched healthy controls (HCs) underwent transcranial magnetic stimulation over M1, eliciting motor-evoked potentials (MEPs) in targeted hand muscles, while they were either at rest or preparing a left- or right-hand response in an instructed-delay choice reaction time task. Preparatory suppression was assessed by expressing MEP amplitudes during movement preparation relative to rest.

Results
Contrary to HCs, PD patients showed a lack of preparatory suppression when the side of the responding hand was analyzed, especially when the latter was the most affected one. This deficit, which did not depend on dopamine medication, increased with disease duration and also tended to correlate with motor impairment, as measured by the Movement Disorder Society Unified Parkinson's Disease Rating Scale, Part III (both total and bradykinesia scores).

Conclusions
Our novel findings indicate that preparatory suppression fades in PD, in parallel with worsening motor symptoms, including bradykinesia. Such results suggest that an alteration in this marker of intact movement preparation could indeed cause motor slowness and support its use in future studies on the relation between M1 alterations and motor impairment in PD. © 2022 International Parkinson and Movement Disorder Society.
Original languageEnglish
JournalMovement Disorders
DOIs
Publication statusE-pub ahead of print - 19 Sep 2022

Keywords

  • Parkinson’s disease
  • Motor cortex
  • Bradykinesia
  • Motor control
  • Transcranial magnetic stimulation

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