# The TMS-evoked potential as a measure of cortical excitation and inhibition during cognitive processes

> **NIH NIH R21** · UNIVERSITY OF IOWA · 2024 · $427,625

## Abstract

ABSTRACT
Non-invasive recordings of human brain activity – be it of BOLD or neural field potentials – all share a common,
insurmountable weakness: it is impossible to identify whether amplitude changes to these signals are due to the
excitation or inhibition of their neural generators (i.e., the underlying patches of cortex). Hence, there is a critical
need to develop non-invasive measures of the moment-to-moment physiological excitability of the human cortex.
 Such a method exists for primary motor cortex. The TMS-induced motor evoked potential (MEP) in the
electromyogram indexes the physiological excitability of cortico-motor tracts originating in primary motor cortex
(M1). The MEP increases alongside motor-neuron firing during movement preparation and decreases alongside
reductions in M1 firing during movement cancellation. Here, we aim to test whether a signal with similar
properties can be derived outside of M1. Specifically, we aim to test whether the TMS-evoked potential (TEP)
in EEG recordings from human cortex similarly reflects changes in the cortical excitability of that underlying
cortex evoked by cognitive processes. The TEP is an EEG amplitude deflection that occurs after single pulses
of TMS applied anywhere on the brain.
 We will use a cognitive task to differentially induce the excitation and inhibition of the same cortical region
outside of M1: the frontal eye fields (FEF). The firing rate of FEF neurons is known to increase during memory-
guided saccades and decrease during the anticipation of anti-saccades (while notably, non-invasive BOLD
recordings show signaling increases in both conditions). We will perform an MRI-guided, sham-controlled
investigation of combined EEG and TMS to test whether the TEP – unlike fMRI or EEG – faithfully indexes these
changes in task-related neuronal firing. If so, this work would provide fundamentally novel, original method to
non-invasively measure the excitability and inhibition of cortical areas outside of M1.

## Key facts

- **NIH application ID:** 10931205
- **Project number:** 1R21NS137987-01
- **Recipient organization:** UNIVERSITY OF IOWA
- **Principal Investigator:** Jan R Wessel
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $427,625
- **Award type:** 1
- **Project period:** 2024-08-01 → 2026-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10931205

## Citation

> US National Institutes of Health, RePORTER application 10931205, The TMS-evoked potential as a measure of cortical excitation and inhibition during cognitive processes (1R21NS137987-01). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10931205. Licensed CC0.

---

*[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*