Mapping cerebellar granule cell function with novel genetic and optical tools

项目概要/摘要 最近来自多个实验室在人类和动物模型中的证据支持颗粒细胞（GrC）的作用 小脑的通路，代表广泛的感觉、运动和内部信息。经典理论 小脑功能的研究表明，少数GrC（<1%）的活动编码了一个特定的感觉运动背景。 然而，最近的群体水平的GrC胞体钙成像研究表明，群体的GrC编码 感觉和运动事件，以及复杂的属性，如奖励和运动准备。然而，这些研究缺乏 时间分辨率，以确定这些事件和GrC发射之间的特定关系。两项研究设计还 排除了直接确定什么输入途径驱动所观察到的GrC活性模式。全面 要理解由GRC执行的输入-输出转换，就需要能够精确地从解剖学上扰动 特定的下行输入，同时以高时空精度密集地记录所得到的活动模式。 为了解决这一系列方法上的差距，我建议（1）全面开发一种用于遗传学的尖峰计数方法， 通过调整电流传感器特性并创建钙离子的生物物理体内模型， 传感器GCaMP，（2）光遗传学干扰新皮层映射其功能输入到GrCs，同时光学访问 整个小脑表面，和（3）使用啮齿动物的行为任务，以消除歧义的感觉，运动和内部状态 对颗粒细胞活动模式的贡献。这些目标的完成将允许直接测试GRC是否确实 对输入信号进行稀疏表示。我还旨在提供迄今为止最全面的分析， 驱动GrC活动的输入的组成。

Project Summary/Abstract Recent evidence from multiple laboratories in both human and animal models supports a role for the granule cell (GrC) pathway of the cerebellum in representing a wide range of sensory, motor, and internal information. Classical theories of cerebellar function proposed that activity in a small number of GrCs (<1%) encodes a particular sensorimotor context. However, recent population level calcium imaging studies of GrC somata indicate that populations of GrCs encode sensory and motor events, and complex properties such as reward and motor preparation. However, these studies lacked the temporal resolution to identify specific relationships between those events and GrC firing. Both study designs also precluded direct determination of what input pathways drove the observed patterns of GrC activity. A comprehensive understanding of the input-output transform performed by GrCs will require the ability to precisely perturb anatomically specific descending inputs while densely recording the resultant patterns of activity with high spatiotemporal precision. To approach this set of methodological gaps, I propose to (1) holistically develop a spike-counting method for genetically encoded indicators (GECIs) by adjusting current sensor properties and creating a biophysical in vivo model of the calcium sensor GCaMP, (2) optogenetically perturb neocortex to map its functional inputs to GrCs while optically accessing the entire cerebellar surface, and (3) use a rodent behavioral task to disambiguate sensory, motor and internal-state contributions to granule cell activity patterns. Completion of these aims will allow a direct test of whether GrCs indeed make a sparse representation of their input signals. I also aim to provide the most comprehensive analysis to date on the makeup of the inputs that drive GrC activity.