Impact of Anodal Transcranial Direct Current Stimulation on Listening Effort, Mental Fatigue, Tinnitus Annoyance, Working Memory, and Expression of NMDA Receptor Subunits in Adults with Tinnitus

Abstract

Background and Aim: Tinnitus is associated with increased listening effort and reduced Working Memory (WM) during speech comprehension. A practical approach to enhance cognitive processes is transcranial Direct Current Stimulation (tDCS). This study aimed to evaluate the effect of tDCS on listening effort, mental fatigue, tinnitus annoyance, WM, and expression of N-Methyl-D-Aspartate (NMDA) receptor subunits (NR1 and NR2) in the blood of individuals with tinnitus.

Methods: Thirty-two chronic tinnitus participants (aged 30–60 years) were randomly assigned to intervention and control groups. The intervention group received anodal tDCS over the left Dorsolateral Prefrontal Cortex (DLPFC) with electrode on F3 for 20 minutes at 1.5 mA over 10 sessions, while the control group underwent sham tDCS. Pre- and post- intervention assessments included audiometry, tympanometry, tinnitus matching, a dual- task paradigm for measuring listening effort, the visual analogue scale for measuring mental fatigue, the Tinnitus Functional Index (TFI) for measuring tinnitus annoyance, and the N-Back test for WM assessment. Western blot analysis of blood samples measured NR1 and NR2 protein expression.

Results: Compared to the control group, active tDCS significantly reduced listening effort, mental fatigue, tinnitus annoyance (p<0.001) and improved WM (p<0.001). After intervention, the intervention group showed a 27% increase in NR1 and a 50% increase in NR2 expression.

Conclusion: The tDCS over DLPFC can reduce listening effort, mental fatigue, and tinnitus annoyance, and enhance WM in adults with chronic tinnitus, which is associated with improved NR1/NR2 protein expression in blood. These findings highlight the potential role of tDCS in tinnitus rehabilitation.