Habituation of the motion detectors of the crayfish optic nerve: Their relationship to the visually evoked defense reflex

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Abstract
Examination of sustaining units, dimming units, and motion detectors under stimulus conditions associated with defense reflex habituation revealed that only the motion detectors exhibit a response decrement with stimulus repetition. Motion detector habituation was specific to the retinal locus of the repetitive stimulus and thus can provide a basis for the spatially specific component of defense reflex habituation. When stimulated at low repetition rates (2‐‐4 min) the motion detectors exhibited a time course of habituation and spontaneous recovery similar to that observed behaviorally. At high repetition rates (20/mm) the motion detectors exhibited a more rapid rate of habituation than was observed for the defense reflex. Simultaneous recordings of motion detector and cheliped levatory muscle activity revealed consistently significant and frequently substantial positive correlations. Both defense reflex and motion detector habituation were transiently reversed by treatment with the GABA antagonist, picrotoxin (1.8 2.8 mg kg body weight). The action of picrotoxin is likely to be mediated via mechanisms controlling the general level of arousal. It was concluded that the response variations of motion detectors subjected to repetitive stimuli contribute to the habituation of the visually evoked defense refle.