Information Processing in the Electrosensory System

处理复杂的感觉信息以产生行为是大脑的一个主要功能，研究这种整合的一个非常有用的模型系统是弱电鱼的大脑。这些鱼通过特殊的器官产生重复的微弱电信号，并通过全身专门的电感受器检测周围的电场。这种信号被用于社会交流和空间“电定位”，就像蝙蝠或海豚利用回声定位来识别和定位物体一样。一群电鱼和一个有多个无线电台的城市有同样的问题：如果两个独立个体使用的信号频率太近，每一个人都有效地“干扰”了另一个人的信号接收。一些使用高度规则信号的电鱼通过一种被称为“干扰避免反应”（JAR）的行为克服了这个问题；频率稍高的鱼将其发射频率向上移动一点，频率稍低的鱼将其发射频率向下移动一点，以扩大间隔，从而帮助每条鱼在其他鱼的背景环境中识别自己的信号。这种行为要求鱼不仅要识别干扰信号的存在，还要识别自身信号的频率比干扰信号高还是低。最近，人们发现非洲的一些电鱼物种与研究得更好的南非电鱼物种根本没有密切关系，它们也有同样的JAR行为，但显然是通过大脑中的不同回路产生的。该项目使用生理和解剖学技术记录和追踪大脑中单个神经细胞的连接，以阐明非洲鱼的这种反应是如何由大脑控制的。特别强调的是空间和时间模式的两种感觉线索，被称为振幅调制和差分相位调制，这两者都是必不可少的行为。这些结果对于理解类似适应行为的独立进化机制非常重要，对于理解与视觉和听觉等系统中感觉行为相关的大脑组织的一般原理也很重要。

Processing of complex sensory information to generate behavior is a major function of the brain, and one very useful model system for studying this integration has been the brain of weakly electric fish. These fish generate a repetitive weak electrical signal from special organs, and detect the electric field around them by specialized electroreceptors all over the body. The signal is used for social communication and for spatial "electrolocation" in much the way bats or dolphins use echolocation to identify and locate objects. A population of electric fish has the same problem as a city with multiple radio stations: if the signals used by two separate individuals are too close together in frequency, each one effectively "jams" the signal reception of the other. Some electric fish that use highly regular signals have overcome this problem by a behavior called the "jamming-avoidance response" (JAR); the fish with the slightly higher frequency moves its emission frequency up just a bit, and the fish with the slightly lower frequency moves its frequency down just a bit, to widen the separation and so help each fish to identify of its own signal against the background environment of other fish. This behavior requires the fish to recognize not only that the jamming signal is present, but whether its own signal is higher or lower in frequency than the jamming signal. Recently it has been found that some species of electric fish in Africa, not at all closely related to the better-studied South African electric fish species, have the same JAR behavior, but apparently produce it by a different circuit in the brain. This project uses physiological and anatomical techniques of recording and tracing the connections of single nerve cells in the brain to clarify how this response is controlled by the brain in the African fish. Particular emphasis will be on the spatial and temporal patterns of two sensory cues, known as amplitude modulation and differential phase modulation, which both are essen tial for the behavior. The results will be important for understanding mechanisms for the independent evolution of similar adaptive behaviors, and also will be important to understanding general principles of brain organization related to sensory behavior in such systems as vision and hearing.