EEG responses to TMS are sensitive to changes in the perturbation parameters and repeatable over time

Area of Science:

• Neuroscience
• Neurophysiology

Background:

• High-density electroencephalography (hd-EEG) coupled with transcranial magnetic stimulation (TMS) offers a non-invasive method to assess human cortical excitability and connectivity.
• This technique holds potential for longitudinal monitoring of pathological alterations, neuroplasticity, and therapy-induced changes in cortical circuits.
• Limitations in diagnostic applications arise if TMS-evoked potentials are either non-sensitive or non-repeatable.

Purpose of the Study:

• To evaluate the sensitivity and repeatability of TMS/hd-EEG potentials.
• To determine if controlled changes in stimulation parameters and longitudinal measurements yield reliable responses.
• To establish the diagnostic potential of TMS/hd-EEG for tracking cortical circuit dynamics.

Main Methods:

• Controlled variations in TMS stimulation parameters (site, intensity, angle) were applied.
• Longitudinal measurements were conducted on the same day and one week apart in 10 volunteers.
• A Divergence Index (DI) was calculated using non-parametric statistics to quantify differences in TMS-evoked potentials.

Main Results:

• 92 single-subject comparisons were performed to assess TMS-evoked potential similarities/differences.
• An optimal DI threshold of 1.67% was identified via receiver operating characteristic analysis.
• This threshold achieved 96.7% accuracy in detecting changes due to altered stimulation parameters.

Conclusions:

• EEG responses to TMS reflect deterministic properties of neuronal circuits, not random variability.
• TMS-evoked potentials demonstrate sensitivity to changes and repeatability over time.
• The findings support the use of TMS/hd-EEG for detecting longitudinal changes in cortical circuit states.