Can topical application of numbing cream improve the efficacy of sham TDCS?

Abstract Introduction: Transcranial Direct Current Stimulation (TDCS) can modulate intrinsic cortical activity by stimulating specific brain areas. TDCS produces peripheral somatosensory co-stimulation that may contribute to the neuro-modulatory effects and hamper effective blinding. Objective: To assess how topical administration of numbing cream modifies subjective tingling experience during sham relative real in focal vs. non-focal high- versus low-intensity stimulation settings. Methods: 30 healthy participants received bi-hemispheric targeting hand representation left primary motor cortex (M1-HAND). We compared with a bi-polar montage (7x5cm electrodes) center-surround (3cm diameter central electrodes, surrounded 10cm ring electrodes). was applied randomized blocks 2mA or 4mA (30sec ramp-up, 3min stimulation, 30sec ramp-down) matched conditions ramp-up down). Participants were tested across two days, without anesthetic underneath electrodes. They rated their sensations following each block, 10-level VAS-score. effect experimental factors “numbing cream”, “focality stimulation”, “intensity “sham-real stimulation” on VAS scores using repeated-measures ANOVA non-parametric permutation tests (p<0.05). Results: Tingling more intense high-intensity but not condition (sham-real x intensity interaction, p = 0.011). Topic application generally reduced VAS-ratings, it did alter difference between TDCS, stimulation. Conclusion: While inducing an overall attenuation experience, use does improve matching corresponding conditions. Keywords: effects, cream, tDCS, high