Abstract
Extracellular spike activity from three different types of visual interneurons found in the optic lobe of the giant cockroach Blaberus giganteus was recorded. The spike rate of all three types of neurons fluctuated in a circadian manner in constant darkness (DD). Two types, so-called "on" neurons (ON1 and ON2), responded exclusively to stationary light stimuli. A static light pulse elicited a sustained component in ONI, whereas in ON2 only a brief transient response was observed. In ON1 neurons, responsiveness was high during the subjective night and low during the subjective day. The responsiveness of ON2 neurons had a peak during a few hours around subjective dusk and a smaller peak in the later subjective night. The third neuron type recorded consisted of a directionally selective motion-detecting (DSMD) neuron. The pure intensity response and the motion response of the DSMD neuron were high during the subjective day and low during the subjective night. The results show that visual interneurons in the optic lobes are influenced differently by the circadian oscillator system. It is suggested that the mode of circadian control depends on the role a neuron plays in the process of visual information processing.