Ats thermode

Application of a non-painful warm stimulus (32–34°C) was used as the control session, which was identical to the CPT and HP sessions except for the stimulation temperature used. The warm stimulus was similarly administered in four trials of about 60 seconds each with a 60-second rest/withdrawal period between trials. Participants were asked to rate the warm stimulus using a VAS (0=No pain sensation and 100=Maximal pain sensation). No participants rated any of the control trials as painful. The Pathway (Medoc, USA) was used for the thermal stimulation using a 16×16mm ATS thermode.

Quantitative sensory thresholding (QST) systematically determines information about Ab fibers (sensory), Ad fibers (pain), and C fibers (pain tolerance). We acquired threshold levels by attaching a 30 × 30 mm thermode on the left forearm of participants (ATS thermode Medoc, Durham, NC, USA). Using the Medoc Pathway System, we determined sensory, pain, and tolerance thresholds by administering incremental periods of thermal stimulus beginning at 32 °C and increasing by 0.5 °C per second. Participants were asked to verbally indicate when the stimulus was first detected (sensory), when it was painful (pain), and then pressed a button when the stimulus was intolerable (pain tolerance). When ‘intolerable’ was indicated, the thermode ceased heating and quickly returned to 32 °C. This was repeated for 5 trials to obtain average sensory, pain, and tolerance thresholds. We acquired QST data at baseline and after tFUS (approximately 90 min post-baseline QST, 45 min after initiation of the first tFUS session and 20 min after initiation of the second tFUS session).
As a secondary outcome measure, we recorded pain ratings using an MRI-compatible handpad within the bore of the scanner in an attempt to capture acute pain effects, as well as concurrent tFUS/Pain thresholds. See supplemental methods 1 for description of these secondary methods and findings.