The effect of motor activity on the reactivity of single visual units in the crayfish

Metal microelectrodes were chronically implanted in the optic nerve and circumesophageal commissure of the crayfish. The activity from single units was recorded in freely moving animals, and responsiveness to visual stimuli was found correlated with motor activity of the animal. The lowest firing rate corresponded to states of quietness and the highest to fighting reactions. The two types of visual units studied showed a different degree of modulation. The sustaining fibers, which signal the intensity of illumination, were facilitated at all levels of motor excitation. The movement fibers, which are phasic units, reacted to great enhancements of motor activity by an increased number of spikes in each response to movement, and by a lowering in the rate of “habituation.” This facilitatory influence is neural in origin, presumably conveyed by the “activity” fibers, which run efferently in the optic nerve, carrying information about movement of the various body parts.