There are several fish with small electric organs, called weakly electric fish, that use their own electrical signal for "electrolocation" much as a bat or dolphin uses emitted sound (sonar) for echolocation of objects. Many of these fish produce an ongoing electrical waveform of nearly constant frequency to produce an electrical field around the fish, and special electroreceptors in the skin all over the body detect distortions in this field when objects are nearby. A reflex called the "jamming avoidance response" also is used by some fish to alter their own frequency if there is another signal in the water at close to the same frequency, that otherwise would mask out the fish's own signal. The neural circuits for parts of this detection system are now fairly well known, and a particular area of interest is part of the midbrain called the torus semicircularis. This project will investigate how neurons in the different layers of the torus respond to spatial and temporal changes in signal amplitude and phase, and how those responses are affected in the presence of jamming signals. Extracellular and intracellular recording will be used, along with labelling physiologically characterized neurons with dye to identify their location and connections. Responses will be compared between species with and without the jamming avoidance response, to identify which neural elements of the sensory-to- motor pathway are involved in that stereotyped behavior. This study exploits the well-described circuitry for electrosensory detection and its link to some highly quantifiable behaviors. Results from this novel approach will be valuable to sensory neuroscience in general, because they address problems of signal detection in noise, of motion detection and its discrimination from self-movement, and the functional role of layers in brain structure.
