Magpro stimulator

In order to determine the right M1 hot-spot, motor-evoked potentials of the left fore-arm muscles were elicited by single TMS pulses delivered with a standard figure-of-eight coil (MC-B70, MagPro Stimulator, MagVenture, Willich, Germany). The coil was held tangentially to the scalp with the handle pointing backward and laterally at an angle of about 45° away from the midline. The coil was positioned over the M1 hand area to elicit motor responses. By moving the coil in 0.5 cm steps anterior, posterior, medial, and lateral to this area, the exact localization of the area which evoked the maximal motor response was determined. This location was marked on the scalp with a pen and used for positioning of the tDCS electrode.

Since I-wave latencies and I-wave facilitation display considerable inter-individual variability (23 (link)), we chose to probe PMd-to-M1 connectivity at the inter-pulse interval reflecting the individual I₁-wave peak in each participant. The individual I₁-wave peak was determined using a SICF protocol. The intensity of the TS was set to induce MEPs of about 1 mV in the relaxed right FDI muscle, while the intensity of the CS was set at 90% of Resting Motor Threshold (RMT). Six different inter-stimulus intervals (ISIs) ranging from 1.0 to 2.0 ms (steps of 0.2 ms) were repeated 10 times in pseudorandom order. Trials were averaged for each ISI, and the ISI with the greatest facilitation was used in the subsequent main experiment as ISI between M1-HAND and PMd stimulation. The SICF-curve was measured using an MC-B70 coil connected to a MagPro stimulator (MagVenture, Farum, Denmark). Note that we used a different coil from the ones used for the dual site-TMS session since the small Mag&More coils required for ipsilateral PMD-M1 stimulation did not allow two consecutive pulses to be fired through the same coil at the short inter-pulse intervals required by the SICF. The RMT for both coil types was determined in the relaxed FDI muscle using the Parameter Estimation in Sequential Test (PEST) method (30 (link), 31 (link)).

Stimulation was performed using a MagPro stimulator [MagVenture (distr. Mag2Health), Farum, Denmark] and either a flat B65 coil (MagVenture) in patients with upper limb pain or an angled B70 figure-of-eight coil (MagVenture) in patients with lower limb. Compared to flat figure-of-eight coils, the B70 coil is more powerful, leading to lower the resting motor threshold by 10–33%^{22 (link)} and stimulates deeper the motor cortex corresponding to lower limbs due to its angle of 150°.^{23 (link)}The motor cortical representation of the painful region was targeted using a TMS Navigator system, integrating individual brain MRI data (Localite, Sankt Augustin, Germany). Stimulation was performed at 10 Hz with an intensity set at 80% of the rest motor threshold (previously determined with motor evoked potential recording) and the coil held in posteroanterior orientation. Each rTMS session consisted of 40 trains of 5-s duration with inter-train interval of 25 s for a total of 2000 pulses in 20 min. This protocol is in line with the expert recommendations for safety.^{24 (link),25 (link)}

The left dPMC was localized using a neuronavigation system (LOCALITE, Sankt Augustin, Germany). The target area was pre-defined by Talairach coordinates −29, 5, 47 (x, y, z) corresponding to Brodmann area 6.
To ensure that the target area for stimulation was sufficiently separated from the left M1, the cortical representation of the right first dorsal interosseus (FDI) muscle was localized using single pulse TMS. To this end, a standard figure of eight coil (MC-B70) connected to a MagPro stimulator (Mag Venture, Hückelhoven, Germany) was placed tangentially to the scalp to trigger motor-evoked potentials (MEP). The area evoking the largest motor response was defined as motor hot spot. In two sessions, M1 localization was not possible. The mean distance between M1 hot spot and the PMC target area was 5.11 ± 0.13 cm (sham), 5.08 ± 0.20 cm (anodal) and 4.89 ± 0.21 cm (cathodal). The distance did not differ significantly between sessions (F(2, 30) = 0.456, p = 0.638).