Transcranial random noise stimulation of the primary visual cortex but not retina modulates visual contrast sensitivity

Abstract

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 stimuli when tRNS intensity is optimized for the individual. However, it is currently unknown whether tRNS-induced signal enhancement could be achieved within different neural substrates along the retino-cortical pathway and whether the beneficial effect of optimal tRNS intensities can be reproduced across sessions. 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 (no tRNS, 0.75, 1, 1.5mA) and over the retina (no tRNS, 0.1, 0.2, 0.3mA), 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 on 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. We found that at the group level tRNS of 0.75mA 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 that V1 seems to be more sensitive than the retina to tRNS-induced modulation of visual contrast processing.

Contrast detection is enhanced by non-stochastic, high-frequency transcranial alternating current stimulation with triangle and sine waveform

“…Similar to other studies investigating resonance-like effects (Potok et al, 2022a; van der Groen and Wenderoth, 2016), our results have revealed large variability among participants in terms of the optimal intensity resulting in the strongest modulation of visual contrast sensitivity ( Figure 5B , Figure 6B ). However, consistent with the effects of tRNS-induced online modulation of contrast processing in V1 shown previously (Potok et al, 2022a; van der Groen and Wenderoth, 2016), the effects of individualized hf-tACS intensity were replicated on the independent VCT data set collected within the same experimental session ( Figure 5C , Figure 6C ), suggesting consistent beneficial resonance-like influence of hf-tACS on signal enhancement.…”

“…In both experiments hf-tACS stimulation (hf-tACS triangle in experiment 1 or hf-tACS sine in experiment 2) was delivered with 0.75mA, 1mA, and 1.5mA amplitude (peak-to-baseline), resulting in maximum current density of 60 which is below the safety limits of 167 for transcranial electrical stimulation (Fertonani et al, 2015). These intensities were selected based on previous studies investigating effects of tRNS on contrast sensitivity (Potok et al, 2022a; van der Groen and Wenderoth, 2016).…”

“…Variance is reported as SD in the main text and as SE in the figures. Statistical analysis of hf-tACS triangle and hf-tACS sine effects was analogous to the one performed to test hf-tRNS effects (Potok et al, 2022a).…”

“…We compared the effects of non-stochastic transcranial electrical stimulation (tES, i.e., hf-tACS triangle and hf-tACS sine ) and stochastic tES (i.e., hf-tRNS) on VCT. The data demonstrating the effect of hf-tRNS on VCT were taken from a previous study investigating the effects of hf-tRNS using the same behavioral paradigm (Potok et al, 2022a).…”

“…To target V1 we used an electrode montage that was previously shown to be suitable for visual cortex stimulation (Herpich, 2019;Potok et al, 2022a;van der Groen and Wenderoth, 2016).…”