Object representation and resolution in a computed sensory map

在回声定位蝙蝠的听觉皮质中，到物体的距离用神经元地图表示。这幅图中的神经元只有当从环境中的物体(如昆虫或其他猎物)反射的回声在蝙蝠发出叫声后以特定的延迟到达时，才会产生动作电位。与所谓的结构图不同的是，结构图只是反映外围传感器上皮表面的地形组织(例如，视网膜在初级视觉皮质中被表示)，这种所谓的目标距离图是计算地图。这些映射包含来自神经计算的感觉信息的表示。在这里，叫声发射和回声到达之间的延迟是在蝙蝠听觉系统的神经电路中计算的。其他脊椎动物的空间听觉计算地图也被报道过。这项建议旨在研究蝙蝠变色竹口鱼目标距离地图中沿空间深度轴排列的多个物体的表征。单电极和多电极阵列的细胞外记录被用来揭示在映射中可以同时表示多少个对象，以及单个神经元可以分辨两个对象的最小距离。此外，还将研究空间布置(即，对象在方位和仰角上的位置)对对象分辨率和表示的影响。这些结果将使我们深入了解脊椎动物听觉系统中计算地图的基本功能原理。

In the auditory cortex of echolocating bats, the distance to an object is represented in a neuronal map. Neurons in this map only fire action potentials if echoes reflected from objects in the environment (e.g. insects or other prey items) arrive with a specific delay after the bat has emitted a call. In contrast to so-called structural maps, which simply reflect the topographic organization of the epithelial surface of a peripheral sensor (e.g. the retina is represented in the primary visual cortex), this so-called map of target-distance is a computational map. These maps contain a representation of sensory information that is derived from neural computation. Here, the delay between call emission and echo arrival is computed within the neural circuitry of the bats’ auditory system. Computational maps for spatial hearing have also been reported for other vertebrates.This proposal aims to investigate the representation of multiple objects arranged along the spatial depth axis in the map of target-distance in the bat Phyllostomus discolor. Extracellular recordings with single electrodes and multi-electrode arrays are employed to reveal how many simultaneously present objects can be represented in the map, and up to which minimal distance two object can be resolved by single neurons. Further, the influence of the spatial arrangement (i.e., the position of objects in azimuth and elevation) on object resolution and representation will be investigated. The results will give insight into the basic functional principles of computational maps in the auditory system of vertebrates.