Phase coding by grid cells in unconstrained environments: two‐dimensional phase precession

Action potential timing is thought to play a critical role in neural representation. For example, theta phase precession is a robust phenomenon exhibited by spatial cells of the rat entorhinal–hippocampal circuit. In phase precession, the time a neuron fires relative to the phase of theta rhythm (6–10 Hz) oscillations in the local field potential reduces uncertainty about the position of the animal. This relationship between neural firing and behavior has made precession an important constraint for hypothetical mechanisms of temporal coding. However, challenges exist in identifying what regulates the spike timing of these cells. We have developed novel analytical techniques for mapping between behavior and neural firing that provide sufficient sensitivity to examine features of grid cell phase coding in open environments. Here, we show robust, omnidirectional phase precession by entorhinal grid cells in openfield enclosures. We present evidence that full phase precession persists regardless of how close the animal comes to the center of a firing field. Many conjunctive grid cells, previously thought to be phase locked, also exhibited phase coding. However, we were unable to detect directional‐ or field‐specific phase coding predicted by some variants of models. Finally, we present data that suggest bursting of layer II grid cells contributes to the bimodality of phase precession. We discuss implications of these observations for models of temporal coding and propose the utility of these techniques in other domains where behavior is aligned to neural spiking.     

影像学定位追踪体内微纳米机器人

微纳米机器人是特征尺度为微米或纳米级的小型化机器人,可通过精准导航到达现有医疗器械难以企及的人体区域,在靶向递送、微创手术、健康监测等方面具备良好的应用前景。实时高分辨率影像学定位追踪是完成微纳米机器人体内精准导航的先决条件。本文对影像学定位追踪体内微纳米机器人研究进展进行综述。