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Updated: May 10, 2026
Assessing Primary Motor Cortex Excitability and Excitability Modulation by Pairing Transcranial Magnetic Stimulation with Electromyography
Published on: October 7, 2025
Median nerve stimulation modulates extracellular signals in the primary motor area of a macaque monkey
Odysseas Papazachariadis1, Vittorio Dante, Stefano Ferraina
1Department of Physiology and Pharmacology, Sapienza University, 00185 Rome, Italy.
Abstract:
Aiming to better define the functional influence of somatosensory stimuli on the primary motor cortex (M1) of primates, we investigated changes in extracellular neural activity induced by repetitive median nerve stimulation (MNS). We described neural adaptation and signal integration in both the multiunit activity (MUA) and the local field potential (LFP). To identify integration of initial M1 activity in the MNS response, we tested the correlation between peak amplitude responses and band energy preceding the peaks. Most of the sites studied in the M1 resulted responsive to MNS. MUA response peak amplitude decreased significantly in time in all sites during repetitive MNS, LFP response peak amplitude instead resulted more variable. Similarly, correlation analysis with the initial activity revealed a significant influence when tested using MUA peak amplitude modulation and a less significant correlation when tested using LFP peak amplitude. Our findings improve current knowledge on mechanisms underlying early M1 changes consequent to afferent somatosensory stimuli.
Insights
Repetitive median nerve stimulation (MNS) affects primate primary motor cortex (M1) neural activity. Multiunit activity (MUA) showed significant adaptation, while local field potential (LFP) responses were more variable.
Area of Science:
- Neuroscience
- Motor Control
- Somatosensory System
Background:
- The primary motor cortex (M1) plays a crucial role in motor control.
- Understanding how somatosensory stimuli influence M1 is essential for deciphering motor control mechanisms.
Purpose of the Study:
- To investigate the functional influence of somatosensory stimuli on primate M1.
- To characterize neural adaptation and signal integration in M1 following median nerve stimulation (MNS).
Main Methods:
- Recorded extracellular neural activity in primate M1 during repetitive MNS.
- Analyzed multiunit activity (MUA) and local field potential (LFP) responses.
- Correlated M1 activity with preceding neural signals to assess response integration.
Main Results:
- Most M1 sites responded to MNS.
- MUA peak amplitude significantly decreased over time during repetitive MNS.
- LFP response amplitude showed more variability, and MUA peak amplitude modulation correlated more significantly with initial activity than LFP.
Conclusions:
- Repetitive MNS induces neural adaptation in primate M1.
- MUA reflects somatosensory input integration more strongly than LFP in early M1 responses.
- Findings enhance understanding of early M1 changes following afferent somatosensory stimuli.
