Optogenetics uses light to control and observe the activity of neurons, often using a focused laser beam. As brain tissue is a scattering medium, beams are distorted and spread with propagation through neural tissue, and the beam's degradation has important implications in optogenetic experiments. To address this, we present an analysis of scattering and loss of intensity of focused laser beams at different depths within the brains of zebrafish larvae. Our experimental set-up uses a 488 nm laser and a spatial light modulator to focus a diffraction-limited spot of light within the brain. We use a combination of experimental measurements of back-scattered light in live larvae and computational modelling of the scattering to determine the spatial distribution of light. Modelling is performed using the Monte Carlo method, supported by generalised Lorenz-Mie theory in the single-scattering approximation. Scattering in areas rich in cell bodies is compared to that of regions of neuropil to identify the distinct and dramatic contributions that cell nuclei make to scattering. We demonstrate the feasibility of illuminating individual neurons, even in nucleus-rich areas, at depths beyond 100 μm using a spatial light modulator in combination with a standard laser and microscope optics.

中文翻译：

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完整大脑组织中雕刻光的散射，对光遗传学有影响。

光遗传学通常使用聚焦激光束来控制光并观察神经元的活动。由于脑组织是散射介质，因此光束会扭曲并随着在神经组织中的传播而传播，光束的降解在光遗传学实验中具有重要意义。为了解决这个问题，我们提出了斑马鱼幼虫大脑内不同深度的聚焦激光束的散射和强度损失的分析。我们的实验装置使用488 nm激光和空间光调制器将聚焦衍射光斑聚焦在大脑内。我们将活幼虫中背向散射光的实验测量值与散射的计算模型结合起来使用，以确定光的空间分布。使用蒙特卡洛方法进行建模，在单散射近似中得到了广义Lorenz-Mie理论的支持。将富含细胞体的区域中的散射与Neuropil区域中的散射进行比较，以确定细胞核对散射的独特而显着的贡献。我们展示了使用空间光调制器结合标准激光和显微镜光学器件，甚至可以在深度超过100μm的深度照射单个神经元（甚至在富核区域）的可行性。