Effects of transcranial direct current stimulation and transcranial random noise stimulation on working memory and task-related EEG in major depressive disorder.

Objective: To compare effects of transcranial direct current stimulation (tDCS) and transcranial random noise stimulation with a direct-current offset (tRNS + DC-offset) on working memory (WM) performance and task-related electroencephalography (EEG) in individuals with Major Depressive Disorder (MDD).
Methods: Using a sham-controlled, parallel-groups design, 49 participants with MDD received either anodal tDCS (N = 16), high-frequency tRNS + DC-offset (N = 16), or sham stimulation (N = 17) to the left dorsolateral prefrontal cortex (DLPFC) for 20-minutes. The Sternberg WM task was completed with concurrent EEG recording before and at 5- and 25-minutes post-stimulation. Event-related synchronisation/desynchronisation (ERS/ERD) was calculated for theta, upper alpha, and gamma oscillations during WM encoding and maintenance.
Results: tDCS significantly increased parieto-occipital upper alpha ERS/ERD during WM maintenance, observed on EEG recorded 5- and 25-minutes post-stimulation. tRNS + DC-offset did not significantly alter WM-related oscillatory activity when compared to sham stimulation. Neither tDCS nor tRNS + DC-offset improved WM performance to a significantly greater degree than sham stimulation.
Conclusions: Although tDCS induced persistent effects on WM-related oscillatory activity, neither tDCS nor tRNS + DC-offset enhanced WM performance in MDD.
Significance: This reflects the first sham-controlled comparison of tDCS and tRNS + DC-offset in MDD. These findings directly contrast with evidence of tRNS-induced enhancements in WM in healthy individuals.
Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: In the last three years PBF has received equipment for research from Neurosoft, Nexstim and Brainsway Ltd. PBF has served on scientific advisory boards for Magstim and LivaNova and acted as a founder and board member for TMS Clinics Australia and Resonance Therapeutics. All other authors have no conflicts to report.
(Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)