Fig. 1

Stimulation device and stimulation designs. A Traveling wave (TW) and blocked design (BD) consist of two stimulation directions: Forward (Fw; upper row) with stimulation moving from D1 to D5 and Backward (Bw; lower row) with stimulation moving from D5 to D1. The TW consists of 4 s stimulations of each digit, repeated 15 times in both stimulation directions. The BD consists of 12 s stimulations of each digit and a 12 s non-stimulation rest period (gray) after every fourth digit stimulation. TW was analyzed using cross correlation with two predictors per digit shifted by one TR (2 s). BD was analyzed using a standard GLM analysis with one predictor per digit. B Mini piezotactile stimulators (mPTS) with a round, MRI-compatible, metal probe (left panel), delivering a 25 Hz vibrotactile stimulation, were attached to the most distal phalanx of all five digits of the participants right hand (right panel). C The order of the stimulation designs within the two sessions was counterbalanced across the participants by assigning them to either Version A or B. In each version, both sessions began with the Fw runs of the two designs, starting with either BD or TW (counterbalanced across sessions). Then, the Bw runs were acquired in the opposite order. During the first session, multiple other measures not relevant for the current experiment (MoM) were acquired between the Fw and Bw runs. In the second session, MoM were acquired after the Bw runs. Lastly, the T1-weighted scans (T1w) were always preceded and followed by functional scans with reversed phase encoding direction (RP), required for EPI distortion correction of the functional scans of interest. All sessions ended with the acquisitions of MoM