Domain-Specific Effects of Transcranial Direct Current Stimulation in Chronic Lower Back Pain: A Bayesian Internal Meta-Analysis

Chronic pain is associated with deficits in cognitive functioning and increased pain intensity. Research investigating the potential for transcranial direct current stimulation (tDCS) to improve cognitive functioning, pain experience, and psychological health in individuals with chronic lower back pain (CLBP) yield mixed results. The present randomised, placebo-controlled study examined the impact of anodal-tDCS over left-dorsolateral prefrontal cortex (left-DLPFC) on cognitive functioning, pain experience, and psychological health in those with CLBP. Thirty participants with CLBP (Mage = 57.47 years, SDage = 14.28 years) received 20-minutes of sham or anodal tDCS, twice weekly, for 4 weeks. Twenty-six outcomes across five functional domains were assessed at baseline and post-intervention. Bayesian multilevel models estimated intervention effects for each outcome, and an internal meta-analysis synthesised domain-level effects. Results revealed robust cognitive enhancement for Executive Function/Attention (pooled effect 0.21 SD, 95% highest posterior density [HPD] [0.03, 0.40]), with the largest effect observed for Letter Number Sequencing (0.56 SD, 95% HPD [0.09, 1.04]). Pain & Physical Function showed borderline effects (0.18 SD, 95% HPD [-0.03, 0.38]), while Mood & Wellbeing showed negligible effects (0.03 SD, 95% HPD [-0.15, 0.22]). These findings demonstrate domain-specific effects, with selective cognitive improvements but unclear analgesic effects and no mood benefits. Anodal tDCS may improve cognitive deficits in CLBP but should not be considered a standalone intervention for pain or mood. Future research should examine alternative cortical targets for pain relief and potential synergistic effects with psychological interventions.