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

Marie Louise Liu, Kristoffer Madsen, Axel Thielscher, Hartig Roman Siebner

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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 the subjective tingling experience during sham relative to real TDCS in focal vs. non-focal and high- versus low-intensity stimulation settings.
Methods: 30 healthy participants received bi-hemispheric TDCS targeting the hand representation of the left primary motor cortex (M1-HAND). We compared non-focal TDCS with a bi-polar montage (7x5cm electrodes) and focal TDCS with a center-surround montage (3cm diameter central electrodes, surrounded by 10cm diameter ring electrodes). TDCS was applied with randomized blocks of 2mA or 4mA (30sec ramp-up, 3min stimulation, 30sec ramp-down) and matched sham conditions (30sec ramp-up and down). Participants were tested across two days, with and without anesthetic cream applied underneath the electrodes. They rated their sensations of tingling following each stimulation block, with a 10-level VAS-score. We tested the effect of the experimental factors “numbing cream”, “focality of stimulation”, “intensity of stimulation”, and “sham-real stimulation” on VAS scores using repeated-measures ANOVA and non-parametric permutation tests (p<0.05).
Results: Tingling was more intense during real TDCS relative to sham TDCS in the high-intensity but not low-intensity condition (sham-real x intensity interaction, p = 0.011). Topic application of numbing cream generally reduced VAS-ratings, but it did not alter the relative difference in tingling experience between real and sham TDCS, high-intensity and low-intensity TDCS, focal and non-focal stimulation.
Conclusion: While inducing an overall attenuation of tingling experience, the use of numbing cream does not improve the matching of tingling experience between corresponding sham and real TDCS conditions.
Original languageEnglish
JournalBrain Stimulation
Volume14
Issue number6
Pages (from-to)1668
Number of pages1
ISSN1935-861X
DOIs
Publication statusPublished - 2021

Keywords

  • Peripheral effects
  • Numbing cream
  • Sham tDCS
  • Focal high intensity

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