Exploring Motor Network Connectivity in State-Dependent Transcranial Magnetic Stimulation: A Proof-of-Concept Study

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Brain Network Dynamics

Background:

• Non-invasive brain stimulation (NIBS) variability is often studied using local electroencephalography (EEG) features.
• The brain's intrinsic long-range network organization is crucial for understanding complex neural processes.
• State-dependent NIBS approaches are emerging to account for dynamic brain states.

Purpose of the Study:

• To investigate the relationship between primary motor cortex (M1) EEG connectivity and the Motor Network (MN).
• To determine how MN functional connectivity influences responses to transcranial magnetic stimulation (TMS) of M1.
• To explore the potential of using MN connectivity for personalized NIBS.

Main Methods:

• Simultaneous EEG and TMS were applied to eight subjects at rest, delivering 1000 TMS pulses to the left M1.
• Motor-evoked potentials (MEPs) were recorded from the right hand.
• Source space functional connectivity of the left M1 was analyzed using the imaginary part of the phase locking value at the μ-rhythm frequency.

Main Results:

• Group-level analysis identified functional connections between the left M1, supplementary motor area, and right M1.
• TMS pulses delivered during high MN connectivity states yielded significantly greater MEP amplitudes compared to low connectivity states.
• The relationship between MN connectivity and MEP amplitude was more pronounced in individuals with higher cortico-spinal excitability.

Conclusions:

• Pre-stimulation M1 EEG connectivity reflects MN organization.
• MN connectivity state is a significant modulator of M1 TMS responses.
• This study supports the development of MN connectivity-based NIBS for improved efficacy and personalization.