Related Experiment Video
Updated: Jan 3, 2026
Neuroimaging-Guided TMS–EEG for Real-Time Cortical Network Mapping
Published on: June 13, 2025
Novel TMS-EEG indexes to investigate interhemispheric dynamics in humans
Elias Paolo Casula1, Michele Maiella2, Maria Concetta Pellicciari3
1Non-Invasive Brain Stimulation Unit/Department of Behavioral and Clinical Neurology, Santa Lucia Foundation, Via Ardeatina 354, 00179 Rome, Italy; Department of Clinical and Movement Neurosciences, UCL Queen Square Institute of Neurology, University College London, Queen Square 33, WC1N 3BG London, United Kingdom.
Objective:
To validate two indexes of interhemispheric signal propagation (ISP) and balance (IHB) by combining transcranial magnetic stimulation (TMS) and electroencephalography (EEG).
Methods:
We used TMS-EEG to non-invasively stimulate the two hemispheres of 50 healthy volunteers and measured interhemispheric dynamics in terms of ISP and IHB. We repeated our evaluation after three weeks to assess the reliability of our indexes. We also tested whether our TMS-EEG measures were correlated with traditional interhemispheric inhibition (IHI), as measured with motor-evoked potentials (MEPs).
Results:
Our main results showed that ISP and IHB (1) have a high reproducibility among all the participants tested; (2) have a high test-retest reliability (3) are linearly correlated with IHI, as measured with MEPs.
Conclusions:
The main contribution of this study lies in the proposal of new TMS-EEG cortical measures of interhemispheric dynamics and in their validation in terms of intra- and inter-subject reliability. We also provide the first demonstration of the correlation between ISP and IHI.
Significance:
Our results are relevant for the investigation of interhemispheric dynamics in clinical populations where MEPs are not reliable.
