Modulation of central pain mechanisms using high‐definition transcranial direct current stimulation: A double‐blind, sham‐controlled study

Abstract

Background:The use of high-definition transcranial direct current stimulation (HD-tDCS) has shown analgesic effects in some chronic pain patients, but limited anti-nociceptive effects in healthy asymptomatic subjects. Methods: This double-blinded sham-controlled study assessed the effects of HD-tDCS applied on three consecutive days on central pain mechanisms in healthy participants with (N = 40) and without (N = 40) prolonged experimental pain induced by intramuscular injection of nerve growth factor into the right hand on Day 1. Participants were randomly assigned to Sham-tDCS (N = 20 with pain, N = 20 without) or Active-tDCS (N = 20 with pain, N = 20 without) targeting simultaneously the primary motor cortex and dorsolateral prefrontal cortex for 20 min with 2 mA stimulation intensity. Central pain mechanisms were assessed by cuff algometry on the legs measuring pressure pain sensitivity, temporal summation of pain (TSP) and conditioned pain modulation (CPM), at baseline and after HD-tDCS on Day 2 and Day 3. Based on subject's assessment of received HD-tDCS (sham or active), they were effectively blinded. Results: Compared with Sham-tDCS, Active-tDCS did not significantly reduce the average NGF-induced pain intensity. Tonic pain-induced temporal summation at Day 2 and Day 3 was significantly lower in the NGF-pain group under Active-tDCS compared to the pain group with Sham-tDCS (p ≤ 0.05). No significant differences were found in the cuff pressure pain detection/tolerance thresholds or CPM effect across the 3 days of HD-tDCS in any of the four groups. Conclusion: HD-tDCS reduced the facilitation of TSP caused by tonic pain suggesting that efficacy of HD-tDCS might depend on the presence of sensitized central pain mechanisms.

Modulating the somatosensory system using high-definition transcranial direct current stimulation

“…6). The dynamic QST results of the healthy subjects without pain (Study I) who were administered either DLPFC+M1-tDCS or Sham-tDCS were compared in Paper III 237 . In the following sections, an overview of the dynamic QST assessments and results are presented.…”

“…The pressure was increased at a rate of 1 kPa/s to a maximum of 100 kPa. Subjects were instructed to rate the pressureinduced pain using a hand-held electronic 10 cm visual analogue scale (VAS, 0 cm meaning 'no pain' and 10 cm meaning 'worst pain imaginable') 237 .…”

“…The PTT was defined as the maximum pressure pain the subject could tolerate. Detailed descriptions of the cuff-pressure algometry assessments are presented in Paper III 237 . To explore the modulatory effects of both the HD-tDCS and the pain model on cuff-pressure sensitivity in the legs, PDT and PTT were included as secondary outcomes in Study III.…”

“…13) subtracted from the first stimulus (green bar in Fig. 13) 24,237,240,251 . It was hypothesized that the active HD-tDCS would reduce the TSP effect 237 .…”

“…13) 24,237,240,251 . It was hypothesized that the active HD-tDCS would reduce the TSP effect 237 . The TSP effect results of the Sham-tDCS group and the DLPFC+M1-tDCS group are shown in Fig.…”