D70 alpha flat coil

A double-pulse protocol was utilized to assess SICI and ICF at rest (Kujirai et al., 1993 (link)). In this protocol, a subthreshold CS was followed by a suprathreshold TS. SICI was tested at ISIs of 1 and 3 ms. ICF at ISIs of 10 and 15 ms, except for MV PA in which technical limitations of the stimulator restrained us from testing a 1 ms interval. The CS was adjusted to 80% of resting motor threshold (RMT) (Kujirai et al., 1993 (link)). The RMT was defined as the minimal output of the stimulator that elicited MEPs with peak-to-peak amplitude of ≥50 μV in at least 5 out of 10 consecutive trials (Groppa et al., 2012 (link)). The TS was adjusted to evoke MEPs of ∼1 mV (Sanger et al., 2001 (link)). The TMS pulses were applied over the left motor hotspot with a figure-of-eight coil. For the MagVenture setup, we used a MC-B70 Butterfly Coil and for the Magstim setup a D70 Alpha Flat Coil, for a comparison of coil specifications please see Table 1. The coil was oriented that the handle pointed backward and ∼45° to the midsagittal line. Twenty trials were recorded for the TS and for each double-pulse paradigm with at an inter-trial-interval of 7 s ± 25%. The order followed a pseudorandom sequence, except for the first two participants in which we used a block randomization for MV PA, due to an earlier version of our trigger setup.

Magnetic stimulation was applied to the left motor area M1 by means of a Magstim Rapid stimulator and a flat alpha coil (D70 Alpha Flat Coil, Magstim Company, Whitland, Dyfed, UK) being held by a support stand (Magstim AFC Support Stand, Magstim Company, Whitland, Dyfed, UK). The coil was oriented at ∼45°, inducing a posterior-to-anterior current flow across the motor cortex, and moved across the left motor cortex while delivering stimulation in order to locate the optimal coil position to stimulate FCR (Rossini et al. 2015 (link)). The position was marked with a non-permanent marker to ensure consistency of recordings over the session. The positions and orientations of the coil was monitored continuously, and if necessary, adjusted to align with the scalp markings. During all the interventions, the stimulation was controlled through Spike2 (Cambridge Electronic Design, Cambridge, UK) software. We estimated for each subject an individual resting MT, the smallest intensity of stimulation necessary to elicit peak-to-peak MEP amplitudes of at least 50 μV in at least 5 out of 10 trials with 5 s IPIs, following the relative frequency method (Rossini et al. 1994 (link)). MT values were used to calculate the intensities to be set during the recording phase.

We used MagStim Super Rapid² Plus¹ (Magstim Company Ltd., Whitland, UK) stimulation system and D70 Alpha Flat Coil (Magstim Company Ltd.) of figure-eight coil. The rTMS was applied at 90% motor threshold that stimulation moved the monkeys’ fingers with an approximately one-half possibility. Stimuli were delivered at the pulse frequency of 5 Hz, each pulse train of 10 s, and intertrain interval of 50 s. Trains were repeated 10 times, and finally generated 500 pulse stimulations (see also Supplementary Method). This stimulation parameter is equivalent to that used for patients with CPSP^{41 (link)–45 (link)}. Sham stimulation was performed by tilting the same coil 90 degrees and the coil was also separated (by more than 20 mm) from their heads.