Commentary: Electro-, loco-, and otromotor components of electric fish behaviour.

As beginning neuroscience students, we are taught that behaviour is controlled via output to various types of effectors, with different types of muscles and glands being the prime examples. Later, when we discover the world of weakly electric fish, we learn that the electric organ also qualifies as an effector and that the electric organ discharge (EOD) is a form of motor output. Typically, one of the first behaviours that we then learn about in detail is the jamming avoidance response (JAR; Bullock et al., 1972). We soon come to appreciate the beauty of the JAR as a behavioural paradigm for studying a complete sensory-motor loop. Because the JAR involves only electromotor output, the full behaviour can be elicited from immobilized animals in the confines of an electrophysiology rig, allowing both neural activity and behavioural output to be monitored simultaneously. Using this powerful approach, Walter Heiligenberg and colleagues were able to functionally map out the neuronal networks controlling the JAR, from sensory input to motor output, at an unprecedented level of detail (Heiligenberg, 1991). The JAR quickly became one of the most compelling examples of a model system in which behavioural analysis was used to extract both cellularand systems-level understanding of neurophysiological function (Konishi, 2006). The electromotor component of electric fish behaviour tends to stand out because it is something unique that other fish do not possess. It is easy to overlook the more mundane components of fish behaviour, like the locomotor system. Just because locomotor systems are commonplace, however, does not mean we should discount their to provide unique insights into electrosensory function. Indeed, the seminal experiments by Lissmann and Machin (1958) that first demonstrated a clear sensory role for the EOD were based on locomotor, not electromotor, responses of Gymnarchus. It is via locomotor output that the fish can approach or avoid a target. Lissmann and Machin made use of locomotor responses in a set of conditioning experiments in which fish were trained to choose between objects of different electrical properties (Lissmann and Machin, 1958). In fish, the locomotor system includes muscles that control swimming movements and body posture. In weakly electric fish, the control of body posture has two additional important influences: it determines the position of the electric organ in space and it determines the position and configuration of the electroreceptor array. So, when we speak of the ‘locomotor’ system of weakly electric fish, this is really shorthand for the motor system