Probing intrahemispheric interactions with a novel dual-site TMS setup

Test-retest reliability of intrahemispheric dorsal premotor and primary motor cortex dual-site TMS connectivity measures

“…The intrahemispheric modulation of M1 by a preceding CS was probed using a stacked dsTMS set-up using two overlapping figure-of-eight coils, MC-B65HO and MC-B70 to apply CS and TS respectively. The MC-B65HO coil is capable of transmitting pulses through the 1.55 cm thin middle section of the angled MC-B70 coil [see Figure 1A and 1B; more detailed visualization in Hehl et al (2024)]. This enables the stimulation of the PMd and M1 with an interstimulus distance of 2.1 cm, further referred to as dsTMS (see Figure 1A).…”

“…Additionally, the two coils’ focal stimulation points were aligned to mimic the classic ppTMS setups (see Figure 1B). The setup is described in detail in Hehl et al (2024). For both dsTMS (PMd–M1) and ppTMS (M1–M1), the TS over M1 was delivered using the MC-B70 coil at an intensity eliciting stable MEPs of 1–1.5 mV averaged over 5 consecutive pulses.…”

“…For both dsTMS (PMd–M1) and ppTMS (M1–M1), the TS over M1 was delivered using the MC-B70 coil at an intensity eliciting stable MEPs of 1–1.5 mV averaged over 5 consecutive pulses. The CS intensity was determined based on the rMT of the MC-B65HO coil and upscaled by a correction factor to account for the increased coil-to-cortex distance introduced by stacking the coils: rMT corrected = rMT MC-B65HO x 2.1 [please consult Appendix 1 in Hehl et al (2024) for details regarding this calculationHehl et al (2024)].…”

“…The MC-B65HO coil is capable of transmidng pulses through the 1.55 cm thin middle sec)on of the angled MC-B70 coil [see Figure 1A and 1B; more detailed visualiza)on in Hehl et al (2024)]. This enables the s)mula)on of the PMd and M1 with an inters)mulus distance of 2.1 cm, further referred to as dsTMS (see Figure 1A).…”

“…So far, there is limited research on the reliability of PMd–M1 dsTMS measures although sufficient test-retest reliability is essential for future dsTMS studies. As a solution to the diverse coil placements with large interstimulus distances, we recently introduced and validated a novel dsTMS setup using two stacked figure-of-eight TMS coils (Hehl et al, 2024). This setup allows us to investigate the intrahemispheric PMd–M1 interaction with an interstimulus distance of 2.1 cm while using off-the-shelf TMS equipment.…”