Object representation and resolution in a computed sensory map

在回声定位蝙蝠的听觉皮层中，到物体的距离在神经元地图中表示。图中的神经元只有在蝙蝠发出叫声后，从环境中的物体（例如昆虫或其他猎物）反射的回声经过特定的延迟到达时才会激发动作电位。与简单地反映外围传感器的上皮表面的地形组织（例如，视网膜在初级视觉皮层中表示）的所谓的结构图相反，这种所谓的目标距离图是计算图。这些地图包含来自神经计算的感官信息的表示。在这里，呼叫发射和回声到达之间的延迟是在蝙蝠听觉系统的神经回路中计算的。其他脊椎动物的空间听觉计算图也有报道。本研究旨在研究蝙蝠Phyllostomus discolor在目标距离图中沿着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揭示了有多少同时存在的对象可以表示在地图中，以及两个对象的最小距离可以由单个神经元解决。此外，空间布置的影响（即，对象在方位角和仰角上的位置）对对象分辨率和表示的影响。研究结果将有助于深入了解计算地图在脊椎动物听觉系统中的基本功能原理。

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.