Functional Grouping in Hippocampus

大脑如何表达人们所知道和操纵的信息？对这个核心生物学问题的一个答案是通过“集合编码”。这个想法假设大脑的运作就像一个光矩阵显示器。显示屏中的每个灯泡都类似于单个神经元，灯泡的亮度类似于该神经元的电活动。一个显示器可以表达许多信息，类似地，一个集合神经代码可以通过活跃和不活跃神经元的特定和动态模式来表达任何东西。没有一个神经元对任何信息都是必不可少的，每个神经元都参与了许多信息。如果显示器中的相同灯泡同时用于表达两个信息，则重叠的图案合并，导致灾难性的信息丢失。相比之下，大脑善于表达多种甚至相互冲突的想法，但我们不知道这是如何实现的。当两种信息以一种整体编码的形式表达时，如何避免灾难的发生，这个项目正在进行电生理学研究，通过记录大鼠海马体中许多神经元在缓慢旋转的圆盘上的记录。设置条件，使大鼠必须知道它们在旋转盘和静止室中的位置。一些神经元的活动信号磁盘的位置和其他神经元的活动信号静止的房间的位置。在相同的记录中很少观察到海马编码和房间编码活动，表明海马活动根据这两种类型的信息进行功能分组。该项目将确定这种功能分组的发生是因为磁盘编码神经元在解剖学上与房间编码神经元分离，还是因为一个功能组中神经元的活动抑制了另一组中神经元的活动。还将确定这种功能分组是否是习得的，在某种意义上反映了认知经验的组织。这些答案将有助于确定大脑如何解决集成编码思想的基本挑战。在这个项目的过程中，学生将接受电生理记录和行为分析方面的培训，并将通过出版物和国家会议报告来介绍他们的研究结果。

How does the brain express the information people know and manipulate? One answer to this central biological question is by "ensemble coding". This idea postulates that the brain operates like a light-matrix display. Each light bulb in the display is analogous to a single neuron and the brightness of a bulb is analogous to the electrical activity of that neuron. A display can express many messages, similarly, an ensemble neural code can express anything by specific and dynamic patterns of active and inactive neurons. No single neuron is essential for any message and each neuron participates in many messages. If the same bulbs in a display are used to express two messages at once, the overlapping patterns merge causing catastrophic information loss. In contrast, brains are good at expressing multiple, even conflicting ideas, but it is unknown how this is achieved. How the catastrophe is avoided when two messages are expressed in an ensemble code is being investigated electrophysiologically in this project, by recording from many neurons in the hippocampus of rats on a slowly-rotating disk. Conditions are arranged so that the rats must know where they are both on the rotating disk and in the stationary room. The activity of some neurons signals rotating-disk locations and the activity of other neurons signals stationary-room locations. Disk-coding and room-coding activity is rarely observed in the same recordings, indicating hippocampal activity is functionally grouped according to the two types of information. The project will determine whether this functional grouping occurs because disk-coding neurons are anatomically separated from room-coding neurons, or alternatively, because the activity of neurons in one functional group suppresses the activity of neurons in the other group. It will also be determined whether this functional grouping is learned, in a sense reflecting the organization of cognitive experience. The answers will help identify how the brain solves a fundamental challenge to the ensemble coding idea. In the process of this project students will be offered training in electrophysiological recording and behavioral analyses, and will be expected to present their findings through publications and national conference presentations.