BACKGROUND The oculomotor integrator (OI) in the vertebrate hindbrain transforms eye velocity input into persistent position coding output, which plays a crucial role in retinal image stability. For a mechanistic understanding of the integrator function and eye position control, knowledge about the tuning of the OI and other oculomotor nuclei is needed. Zebrafish are increasingly used to study integrator function and sensorimotor circuits, yet the precise neuronal tuning to motor variables remains uncharacterized. RESULTS Here, we recorded cellular calcium signals while evoking monocular and binocular optokinetic eye movements at different slow-phase eye velocities. Our analysis reveals the anatomical distributions of motoneurons and internuclear neurons in the nucleus abducens as well as those of oculomotor neurons in caudally adjacent hindbrain volumes. Each neuron is tuned to eye position and/or velocity to variable extents and is only activated after surpassing particular eye position and velocity thresholds. While the abducens (rhombomeres 5/6) mainly codes for eye position, in rhombomeres 7/8, a velocity-to-position coding gradient exists along the rostro-caudal axis, which likely corresponds to the oculomotor structures storing velocity and position, and is in agreement with a feedforward mechanism of persistent activity generation. Position encoding neurons are recruited at eye position thresholds distributed across the behaviourally relevant dynamic range, while velocity-encoding neurons have more centred firing thresholds for velocity. In the abducens, neurons coding exclusively for one eye intermingle with neurons coding for both eyes. Many of these binocular neurons are preferentially active during conjugate eye movements and less active during monocular eye movements. This differential recruitment during monocular versus conjugate tasks represents a functional diversification in the final common motor pathway. CONCLUSIONS We localized and functionally characterized the repertoire of oculomotor neurons in the zebrafish hindbrain. Our findings provide evidence for a mixed but task-specific binocular code and suggest that generation of persistent activity is organized along the rostro-caudal axis in the hindbrain.

中文翻译：

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幼虫斑马鱼后脑双眼位置和速度协调的功能结构。

背景技术脊椎动物后脑中的动眼神经积分器（OI）将眼速输入转化为持续位置编码输出，这在视网膜图像稳定性中起着至关重要的作用。为了从机制上理解积分器功能和眼睛位置控制，需要了解 OI 和其他动眼神经核的调节。斑马鱼越来越多地用于研究积分器功能和感觉运动电路，但对运动变量的精确神经元调节仍然没有特征。结果在这里，我们记录了细胞钙信号，同时以不同的慢相眼速度诱发单眼和双眼视动眼球运动。我们的分析揭示了外展核中运动神经元和核间神经元以及尾部相邻后脑体积中动眼神经元的解剖分布。每个神经元都会在不同程度上适应眼睛位置和/或速度，并且仅在超过特定眼睛位置和速度阈值后才被激活。虽然外展神经（菱形节 5/6）主要编码眼睛位置，但在菱形节 7/8 中，沿着头尾轴存在速度到位置编码梯度，这可能对应于存储速度和位置的动眼神经结构，并且与持续活动生成的前馈机制一致。位置编码神经元在分布于行为相关动态范围内的眼睛位置阈值处被招募，而速度编码神经元具有更集中的速度放电阈值。在外展神经中，专门编码一只眼睛的神经元与编码双眼的神经元混合在一起。许多双眼神经元在共轭眼球运动期间优先活跃，而在单眼眼球运动期间不太活跃。单眼任务与共轭任务期间的这种差异募集代表了最终共同运动通路的功能多样化。结论我们对斑马鱼后脑动眼神经元的全部进行了定位和功能表征。我们的研究结果为混合但特定于任务的双眼编码提供了证据，并表明持续活动的产生是沿着后脑的头尾轴组织的。