Motor-evoked modules obtained from transcranial magnetic stimulation

Area of Science:

• Neuroscience
• Motor Control
• Neuromodulation

Background:

• Transcranial magnetic stimulation (TMS) is a noninvasive technique used to study the motor system via motor-evoked potentials (MEPs).
• Conventional analysis of MEPs typically focuses on amplitude measures of individual muscles.
• A more comprehensive understanding of corticospinal output requires analyzing pattern-level structures across multiple muscles.

Purpose of the Study:

• To apply a factorization approach to multimuscle MEPs to characterize the pattern-level structure of corticospinal outputs.
• To investigate how different TMS stimulus parameters influence this pattern-level structure.
• To introduce motor-evoked modules (MEMs) as a novel framework for motor system investigation.

Main Methods:

• Utilized non-negative matrix factorization (NMF) to extract motor-evoked modules (MEMs) from multimuscle MEP datasets.
• Analyzed data from three experiments in healthy young adults, varying stimulus intensity, motor mapping size, and paired-pulse TMS paradigms.
• Compared the structure of MEMs across these different experimental conditions.

Main Results:

• MEM structure was significantly impacted by stimulus intensity, demonstrating its role in shaping corticospinal output patterns.
• Varying the motor mapping size had a minimal effect on MEM structure, indicating stability in corticospinal output patterns.
• Paired-pulse TMS, designed to activate intracortical inhibition, altered MEM structure compared to single-pulse TMS.

Conclusions:

• The MEM framework provides a method to characterize the pattern-level structure of corticospinal outputs beyond single-muscle MEP analysis.
• Stimulus intensity and intracortical inhibition are key factors influencing the pattern-level structure of TMS-evoked motor responses.
• MEMs offer a novel perspective and complement existing analyses for investigating the human motor system.