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：

---

完整脑组织中雕刻光的散射，对光遗传学的影响。


光遗传学使用光来控制和观察神经元的活动，通常使用聚焦激光束。由于脑组织是一种散射介质，光束会扭曲并通过神经组织传播，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，我们分析了斑马鱼幼虫大脑内不同深度聚焦激光束的散射和强度损失。我们的实验装置使用 488 nm 激光器和空间光调制器将衍射限制的光点聚焦在大脑内。我们结合使用活幼虫中背向散射光的实验测量和散射的计算模型来确定光的空间分布。建模使用 Monte Carlo 方法进行，并得到单散射近似中广义 Lorenz-Mie 理论的支持。将富含细胞体的区域的散射与神经细胞区域的散射进行比较，以确定细胞核对散射的独特而巨大的贡献。我们证明了使用空间光调制器结合标准激光器和显微镜光学元件，即使在细胞核丰富的区域，也能在超过 100 μm 的深度照亮单个神经元的可行性。