Stochastic Resonance (SR) describes a phenomenon where an additive noise (stochastic carrier-wave) enhances the signal transmission in a nonlinear system. In the nervous system, nonlinear properties are present from the level of single ion channels all the way to perception and appear to support the emergence of SR. For example, SR has been repeatedly demonstrated for visual detection tasks, also by adding noise directly to cortical areas via transcranial random noise stimulation (tRNS). We mathematically show that high-frequency, non-stochastic, periodic signals can yield resonance-like effects with linear transfer and infinite signal-to-noise ratio at the output. Here we tested this prediction empirically and investigated whether non-random, high-frequency, transcranial alternating current stimulation (hf-tACS) applied to visual cortex could induce resonance-like effects and enhance performance on a visual detection task. We demonstrated in 28 participants that applying 80 Hz triangular-waves or sine-waves with hf-tACS reduced visual contrast detection threshold for optimal brain stimulation intensities. The influence of hf-tACS on contrast sensitivity was equally effective to tRNS-induced modulation, demonstrating that both hf-tACS and tRNS can reduce contrast detection thresholds. Our findings suggest that a resonance-like mechanism can also emerge when non-stochastic electrical waveforms are applied via hf-tACS.
New & Noteworthy
Our findings extend our understanding of neuromodulation induced by noninvasive electrical stimulation. We provide first evidence showing acute online benefits of hf-tACStriangleand hf-tACSsinetargeting the primary visual cortex (V1) on visual contrast detection in accordance with the resonance-like phenomenon. The non-stochastic hf-tACS and stochastic hf-tRNS are equally effective in enhancing visual contrast detection.