Abstract
Stochastic resonance (SR) is an inherent and counter-intuitive mechanism of signal-to-noise ratio (SNR) facilitation in biological systems associated with the application of an intermediate level of noise. As a first step to investigate in detail this phenomenon in the somatosensory system, here we examined whether the direct application of noisy light on pyramidal neurons from the mouse-barrel cortex expressing a light-gated channel channelrhodopsin-2 (ChR2) can produce facilitation in somatosensory evoked field potentials. Using anesthetized Thy1-ChR2-YFP transgenic mice, and a new neural technology, that we called Brownian optogenetic-noise-photostimulation (BONP), we provide evidence for how BONP directly applied on the barrel cortex modulates the SNR in the amplitude of whisker-evoked field potentials (whisker-EFP). In all transgenic mice, we found that the SNR in the amplitude of whisker-EFP (at 30% of the maximal whisker-EFP) exhibited an inverted U-like shape as a function of the BONP level. As a control, we also applied the same experimental paradigm, but in wild-type mice, as expected, we did not find any facilitation effects. Our results show that the application of an intermediate intensity of BONP on the barrel cortex of ChR2 transgenic mice amplifies the SNR of somatosensory whisker-EFPs. This result may be relevant to explain the improvements found in sensory detection in humans produced by the application of transcranial-random-noise-stimulation (tRNS) on the scalp.
Highlights
We will start with an explanation of the Stochastic resonance (SR) phenomenon because it is a necessary framework to understand our experimental design and results
Our experimental results show that an intermediate level of optimal Brownian optogenetic-noise-photostimulation (BONP) increased the mean amplitude of the whiskerEFPs for all the six Thy1-ChR2-YFP transgenic mice
We found that the normalized area of signal-to-noise ratio (SNR) (SNRNA) of the whisker-EFPs increased as an inverted U-like shape of the BONP level for all the Thy1-ChR2-YFP transgenic mice
Summary
We will start with an explanation of the SR phenomenon because it is a necessary framework to understand our experimental design and results. Recent studies are attempting to open such “black box,” using the application of electrical noise in the brain to enhance tactile sensation in primates (Medina et al, 2012), or tRNS directly on the scalp in humans The idea behind such pioneering studies is to control the noisy electrical activity of neurons in the cerebral cortex bypassing the noisy sensory stimulation. In a more recent study, Van der Groen and Wenderoth (2016) demonstrated that the electrical tRNS of the visual cortex in humans enhance the detection accuracy of visual stimuli Because such detection accuracy followed an inverted U-like shape, these authors described it as an SR phenomenon. It is desirable that such new technique could be used to examine the impact of the neuronal noise in the brain on the amplitude of the electrophysiological-evoked sensory responses recorded in the same region of noise stimulation
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