Aperiodic neural activity predicts cortical excitability in TMS-EEG

  1. Timo van Hattem
  2. Juliana R. Hougland
  3. Juha Gogulski
  4. Pedro C. Gordon
  5. Paolo Belardinelli
  6. Ulf Ziemann
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Abstract

Background

Fluctuating cortical excitability states are inherent to and critical for brain function. They can be probed non-invasively using transcranial magnetic stimulation (TMS) combined with electroencephalography (EEG) by measuring early local TMS-evoked potentials (EL-TEPs). Pre-stimulus periodic neural activity can predict fluctuating excitability states. To what extent aperiodic neural activity represents a marker of cortical excitability has not been explored.

Objectives

We investigated the relationship between pre-stimulus aperiodic and periodic neural activity and EL-TEP amplitude in both the primary motor cortex (M1) and dorsolateral prefrontal cortex (DLPFC).

Methods

Single-pulse TMS was delivered to the left M1 or left DLPFC in 29 and 11 healthy adults, respectively, while EEG was recorded simultaneously. Pre-stimulus EEG was parameterized into aperiodic and periodic components to extract the aperiodic exponent (slope of 1/f-like activity), alpha power (8–13 Hz), and beta power (13–30 Hz). EL-TEP peak-to-peak amplitudes were extracted from approximately 20-65 ms after the TMS pulse.

Results

Aperiodic exponent showed a strong negative relationship with EL-TEP amplitude in both M1 and DLPFC, with steeper 1/f-like slopes associated with smaller EL-TEP amplitudes. Inconsistent relationships were found between alpha and beta power with EL-TEP amplitude across the two regions.

Conclusions

These findings indicate that pre-stimulus aperiodic neural activity influences cortical excitability in both motor and prefrontal areas. Notably, the aperiodic exponent exhibited stronger associations with cortical excitability compared to periodic alpha or beta power. Brain-state-dependent protocols may benefit from real-time extraction of aperiodic exponent as a target feature to improve the precision and efficacy of TMS.

Highlights

  • Pre-stimulus aperiodic exponent predicts EL-TEP amplitude in M1 and DLPFC.

  • Larger aperiodic exponent is associated with smaller EL-TEP amplitudes.

  • Periodic alpha and beta power do not consistently influence EL-TEP amplitude.

  • Aperiodic exponent may inform brain-state-dependent and closed-loop TMS.

Article activity feed

  1. Version published to 10.64898/2026.10.18.759941 on bioRxiv