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Assessing Primary Motor Cortex Excitability and Excitability Modulation by Pairing Transcranial Magnetic Stimulation with Electromyography
Published on: October 7, 2025
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Motor-cortex excitability and response variability following paired-associative stimulation: a proof-of-concept study
M Campana1,2, I Papazova1, B Pross1
1Department of Psychiatry and Psychotherapy, Ludwig-Maximillian's-University of Munich, LMU, Nußbaumstr. 7, 80336, Munchen, Germany.
Experimental Brain Research
|April 27, 2019
Summary
Individualized paired-associative stimulation (iPAS) may reduce response variability in transcranial magnetic stimulation (TMS) studies. This proof-of-concept study suggests iPAS, by accounting for individual conduction times, could decrease inter-individual differences in motor-evoked potentials (MEP).
Area of Science:
- Neuroscience
- Neurophysiology
- Neuromodulation
Background:
- Paired-associative stimulation (PAS) shows variable efficacy and response across individuals.
- Current PAS protocols lack methods to mitigate inter-individual response variability.
- Understanding and reducing variability is crucial for reliable neuromodulation outcomes.
Purpose of the Study:
- To investigate if an individualized PAS (iPAS) paradigm can reduce response variability.
- To compare the effects of fixed inter-stimulus intervals (ISI) versus iPAS on motor-evoked potentials (MEP).
- To explore the impact of accounting for individual conduction times on PAS efficacy.
Main Methods:
- A within-subjects design with 21 participants assessed three PAS paradigms.
- Participants received fixed 25 ms (PAS 25) and 22 ms (PAS 22) ISI, and an individualized ISI (iPAS) protocol.
- Changes in transcranial magnetic stimulation (TMS)-elicited motor-evoked potentials (MEP) were measured post-stimulation.
Main Results:
- No significant increase in post-stimulation MEP magnitudes was observed across all tested PAS paradigms.
- Exploratory analysis indicated increased inter-individual variability with fixed ISI (PAS 25, PAS 22).
- The iPAS paradigm showed a trend towards higher rates of expected MEP magnitude increases and potentially lower inter-individual variability.
Conclusions:
- Findings suggest a potential association between individually tailored ISI (iPAS) and reduced inter-individual variability in PAS.
- The study highlights the challenge of intra-individual variability in PAS paradigms.
- Further large-scale, replicated studies are necessary to confirm these proof-of-concept findings.
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