Objective: To assess the correlates TMS evoked potentials (TEPs) measurements changes representing interhemispheric transmission to the change in motor symptoms in ‘off’ versus ‘on’ states.
Background: As Parkinson’s disease (PD) advances, levodopa (LD) therapy is complicated by disabling motor and non-motor fluctuations that evolve as a result of progressive nigrostriatal dopaminergic denervation, decreased absorption of oral LD medications, and it’s short half-life. During the LD on–off oscillations, individual doses of LD produce symptom control (‘on’ state), which is replaced by the ‘off’ state when the drug effects have worn off and symptoms recur. Identifying neural activity biomarkers of brain disease is essential to identify their underlying mechanisms ,monitor disease severity and obtain reliable feedback regarding therapeutic efficacy.
Method: Patients with PD experiencing motor fluctuations underwent Delphi, a non-invasive test that probes brain network response, using TMS-EEG and were also evaluated by the MDS-UPDRS in the ‘off’ and then ‘on’ state. Right and left M1, DLPFC and V1 single TMS stimulations were applied with simultaneous EEG registration and then processed and analyzed. Motor fluctuations were quantified as the change in MDS-UPDRS III between the two conditions.
Results: At this point data from 7 patients is presented. Interhemispheric signal propagation (ISP) of the DLPFC network was significantly decreased in ON versus OFF state (t=3.13, p=0.016, Cohen’s d=1.2). A lower M1 ISP at baseline was predictive of a larger change in symptoms (R2=0.776, p=0.02) following LD dose.
Conclusion: Properties of Interhemispheric transmission, probed with TMS-EEG may indicate response to treatment in fluctuating PD patients, suggesting that interplay of excitatory/ inhibitory balance of transcallosal fibers may moderate the response to treatment in those patients. Future studies should examine this hypothesis further.
To cite this abstract in AMA style:
M. Roitman, S. Anis, A. Suminski, N. Zifman, H. Fogel, T. Fay-Karmon, S. Hassin-Baer. TMS-EEG Provides Objective Neurophysiological Measures of Motor Fluctuations in Parkinson’s Disease [abstract]. Mov Disord. 2025; 40 (suppl 1). https://www.mdsabstracts.org/abstract/tms-eeg-provides-objective-neurophysiological-measures-of-motor-fluctuations-in-parkinsons-disease/. Accessed October 7, 2026.« Back to 2025 International Congress
MDS Abstracts - https://www.mdsabstracts.org/abstract/tms-eeg-provides-objective-neurophysiological-measures-of-motor-fluctuations-in-parkinsons-disease/