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

In recent years, dual-coil paired-pulse transcranial magnetic stimulation (ppTMS) has garnered interest for its potential in elucidating neural circuit dynamics. In this study, the dual-coil ppTMS was utilized to assess the effective connectivity between the supplementary motor complex (SMC) and the primary motor cortex (M1) in humans. A robust facilitatory connection between the SMC and M1 was observed, manifested as a 19% increase in mean peak-to-peak motor-evoked potentials following preconditioning of SMC 7 ms prior to M1 stimulation. Importantly, the facilitatory influence of SMC only occurred when the preconditioning stimulation was administered 4 cm anterior to Cz but not when applied at 5-cm, 6-cm, or 7-cm distance. While previous work has focused on demonstrating important temporal dynamics for SMC-M1 plasticity, the present findings highlight a critical contribution of spatial specificity for modulation of SMC-M1 circuitry.

Highlights

• The conditioned stimulus induced larger MEPs compared to the unconditioned stimulus

• The connectivity between SMC and M1 diminished when the SMC coil was moved forward

• Findings highlight the importance of spatial specificity for modulation of SMC-M1 circuitry