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

Objective Investigating the optimal interstimulus interval (ISI) and the 24-hour test-retest reliability for intrahemispheric dorsal premotor cortex (PMd) – primary motor cortex (M1) connectivity using dual-site transcranial magnetic stimulation (dsTMS). Methods In 21 right-handed adults, left intrahemispheric PMd–M1 connectivity has been investigated with a stacked-coil dsTMS setup (conditioning stimulus: 75% of resting motor threshold; test stimulus: eliciting MEPs of 1–1.5 mV) at ISIs of 3, 5–8, and 10 ms. Additionally, M1–M1 short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were investigated to assess comparability to standard paired-pulse setups. Results Conditioning PMd led to significant inhibition of M1 output at ISIs of 3 and 5 ms, whereas 10 ms resulted in facilitation (all, p < 0.001), with a fair test-retest reliability for 3 (ICC: 0.47) and 6 ms (ICC: 0.44) ISIs. Replication of SICI (p < 0.001) and ICF (p = 0.017) was successful, with excellent test-retest reliability for SICI (ICC: 0.81). Conclusion This dsTMS setup can probe the inhibitory and facilitatory PMd–M1 connections, as well as reliably replicate SICI and ICF paradigms. Significance The stacked-coil dsTMS setup for investigating intrahemispheric PMd–M1 connectivity offers promising possibilities to better understand motor control.