Modulation of Visual Contrast Sensitivity with tRNS across the Visual System, Evidence from Stimulation and Simulation

Weronika Potok, Alain Post, Valeriia Beliaeva, Marc Bächinger, Antonino M. Cassarà, Esra Neufeld, Rafael Polania, Daniel Kiper, and Nicole Wenderoth, eNeuro 2023, Volume 10, Article No. ENEURO.0177-22.2023, online 01 June 2023; doi:  10.1523/ENEURO.0177-22.2023

Transcranial random noise stimulation (tRNS) has been shown to significantly improve visual
perception. Previous studies demonstrated that tRNS delivered over cortical areas acutely
enhances visual contrast detection of weak stimuli. However, it is currently unknown whether tRNS-induced signal enhancement could be achieved within different neural substrates along the retino-cortical pathway. In 3 experimental sessions, we tested whether tRNS applied to the primary visual cortex (V1) and/or to the retina improves visual contrast detection. We first measured visual contrast detection threshold (VCT; N=24, 16 females) during tRNS delivery separately over V1 and over the retina, determined the optimal tRNS intensities for each individual (ind-tRNS) and retested the effects of ind-tRNS within the sessions. We further investigated whether we could reproduce the ind-tRNS-induced modulation in a different session (N=19, 14 females). Finally, we tested whether the simultaneous application of ind-tRNS to the retina and V1 causes additive effects. Moreover, we present detailed simulations of the induced electric field across the visual system. We found that, at the group level, tRNS decreases VCT compared to baseline when delivered to the V1. Beneficial effects of ind-tRNS could be replicated when retested within the same experimental session but not when retested in a separate session. Applying tRNS to the retina did not cause a systematic reduction of VCT, irrespective of whether the individually optimized intensity was considered or not. We also did not observe consistent additive effects of V1 and retina stimulation. Our findings demonstrate significant tRNS-induced modulation of visual contrast processing in the V1, but not in the retina.

The scientific and technical impact of the study can be summarized as:

• tRNS affects visual contrast detection signal processing in the V1 region but does not appear to influence signal generation/processing in the retina
• The findings can be used to inform development of therapeutical approaches to the management of visual impairment diseases
• The observed inter-subject variability of tRNS-induced contrast detection capability suggests that optimized and personalized protocols of tRNS stimulation, e.g., with personalized models of stimulation, may be required