P224 Heat Pain Threshold increases after dorsolateral prefrontal cortex (DL) rTMS, but not after stimulation at other sites

Introduction There is accumulating evidence that transcranial magnetic stimulation (TMS) induces analgesic effects undergoing experimentally induced pain. While the motor cortex (M1) is the most widely used cortical target for TMS, also dorsolateral prefrontal cortex (DL) is targeted fairly regularly. As the medial prefrontal cortex (MF) also plays a role in the experience of pain, we investigated the analgesic effects of these three stimulation locations as well as a sham stimulation. Methods 16 healthy participants age 23–66 (6 females) underwent a sham-controlled, within-subject, cross-over design including 4 different stimulation sessions. We assessed the effects of 10 Hz neuronavigated rTMS of 4 different stimulation sites on four thermal thresholds. Warmth detection (WDT), cold detection (CDT), heat pain (HPT) and cold pain (CPT) threshold were assessed before and after stimulation. The results for each stimulation site were sham corrected. Results Sham corrected, HPT differed between baseline and post stimulation in DL, but not in any other stimulation location. The other thresholds (WDT, CDT, CPT) were not changed to a statistically significant degree by stimulation at any site. Discussion Our preliminary results suggest that stimulation of DL, but not of M1 or MF, results in higher heat pain thresholds compared to sham stimulation. This is consistent with the study of Borckard et al. (2007), who found higher HPTs after 10 Hz DL rTMS. However we did not find so far an effect of M1 stimulation as Nahmias et al. (2009) had shown. We had expected to find an increase in pain thresholds which did not occur after MF stimulation. No effects of the stimulation were found on detection thresholds as had been shown in other studies. This suggests a specific influence of 10 Hz rTMS over DL on pain, but not on sensory thresholds.