Reticulospinal Control of Rapid Escape Turning Maneuvers in Fishes

SYNOPSIS. In teleost fishes, the C-start is a rapid avoidancemaneuver that steers the animal away from the strike trajectoryof a predator. We review how the axial motor pattern underlyingthis movement is organized by the reticulospinal system. Thissystem includes the prominent Mauthner cells and other identifiableneurons. Typical of reticulospinal cells, the Mauthner neuronhas inputs from auditory, vestibular, and visual areas and hasoutputs to the trunk motoneurons by means of mono- and disynapticcontacts. Because reticulospinal organization and function isconserved among the vertebrates, the Mauthner network is advantageousas a model for understanding control of movement.We developthree major points. First, despite its seeming anatomical simplicity,the escape network is not a simple hierarchial system with onecell that directs the entire movement. We present evidence thatthe escape response is mediated by an array of neurons whichinclude the Mauthner cells. Second, though the firing of thiscell is adequate to result in a major component of the movement,the Mauthner cell is not indispensible for its execution. Thenetwork producing this movement is capable of regulating itsoutput so that the animal produces the normal range of responsesdespite the absence of one of its major contributors. Thesefindings can be accounted for by one of two models, though themost likely one involves lateral interactions, or corollarydischarges, within the array. Third, our recent work also showsthat the movement pattern is generated by a ballistic commandwhich does not rely on movement-induced sensory feedback. Thesesystem properties allow the animal to produce a highly reliableand orchestrated motor command in only 15 msec from sensorystimulus to EMG.