Category: Parkinson's Disease: Neurophysiology
Objective: To evaluate motor cortex inhibition at different stages of Parkinson’s disease (PD).
Background: In PD, striatal dopamine depletion produces profound alterations in the neural activity of cortico-basal ganglia motor loops, leading to dysfunctional motor output. A key regulator of motor output is the balance between excitation and inhibition in the primary motor cortex, which can be assessed in humans with transcranial magnetic stimulation (TMS) techniques. Despite decades of research, whether cortical inhibition is altered in PD remains unclear.
Method: Here we applied paired-pulse TMS protocols in a relatively large sample of PD patients (n=166: 57 de novo, 50 non-dyskinetic, 59 dyskinetic) and healthy controls (n=40). All patients were studied OFF medication. All analyses were performed with fully-automatic procedures, and we systematically considered and excluded several potential confounding factors such as age, gender, resting motor threshold (RMT), EMG background and test motor evoked potential (MEP) amplitude.
Results: We provide definitive evidence that short-interval intracortical inhibition (SICI) is decreased in PD (-34.3±41.1%) compared to healthy controls (-68.9±20.9%; p<0.001). This reduction of SICI was similar in de novo, non-dyskinetic and dyskinetic patients, suggesting that the alteration remains consistent throughout the evolution of the disease. Importantly, SICI was reduced compared to controls also on the less affected side, even in highly asymmetric de novo patients in which the less affected side was minimally symptomatic (lateralized UPDRS=0 or 1, n=23). From a mechanistic perspective, this reduction of SICI was obtained with relatively low-intensity conditioning stimuli (80% of RMT) and was not associated with any significant increase in short-interval intracortical facilitation (SICF) with the same low-intensity conditioning stimuli, supporting the involvement of cortical inhibitory circuits.
Conclusion: These results suggest that loss of cortical inhibition is a very early, possibly prodromal feature of PD.
To cite this abstract in AMA style:
C. Ammann, M. Dileone, C. Pagge, V. Catanzaro, D. Mata-Marín, F. Hernández-Fernández, M.G Monje, A. Sánchez-Ferro, B. Fernández-Rodríguez, C. Gasca-Salas, J.U Máñez-Miró, R. Martínez-Fernández, L. Vela, F. Alonso-Frech, A. Oliviero, J.A Obeso, G. Foffani. Loss of cortical inhibition in Parkinson’s disease [abstract]. Mov Disord. 2020; 35 (suppl 1). https://www.mdsabstracts.org/abstract/loss-of-cortical-inhibition-in-parkinsons-disease/. Accessed June 15, 2025.« Back to MDS Virtual Congress 2020
MDS Abstracts - https://www.mdsabstracts.org/abstract/loss-of-cortical-inhibition-in-parkinsons-disease/