Connectivity between supplementary motor complex and primary motor cortex: a dual-coil paired-pulse TMS study

Area of Science:

• Neuroscience
• Motor Control
• Brain Stimulation

Background:

• Neural circuit dynamics are crucial for understanding brain function.
• Paired-pulse transcranial magnetic stimulation (ppTMS) is a valuable tool for investigating effective connectivity.
• The supplementary motor complex (SMC) and primary motor cortex (M1) play key roles in motor control.

Purpose of the Study:

• To assess the effective connectivity between the SMC and M1 using dual-coil ppTMS.
• To investigate the spatial specificity of SMC modulation on M1.

Main Methods:

• Dual-coil paired-pulse transcranial magnetic stimulation (ppTMS) was applied.
• Motor-evoked potentials (MEPs) were recorded from M1.
• Conditioning stimulation was delivered to the SMC at varying distances anterior to Cz.

Main Results:

• A robust facilitatory connection between SMC and M1 was observed.
• A 19% increase in mean peak-to-peak MEPs was noted when SMC conditioning preceded M1 stimulation by 7 ms.
• SMC's facilitatory influence was specific to stimulation 4 cm anterior to Cz, with no effect at 5, 6, or 7 cm.

Conclusions:

• Dual-coil ppTMS demonstrates a significant facilitatory link between the SMC and M1.
• Spatial specificity is critical for modulating SMC-M1 circuitry, complementing known temporal dynamics.
• These findings advance our understanding of motor system connectivity and plasticity.