The neural basis of catalepsy in the stick insect cuniculina impigra

Abstract

Intracellular records from somata of FETi and SETi were performed during sinusoidal and rampwise stimulation of the femoral chordotonal organ. The responses were larger on average in SETi but this could be random. All other parameters (form of amplitude-frequency plot, phase-frequency plot, half-lives of rise and fall during ramp-wise stimulations) were not significantly different for both neurons. The responses of both neurons are symmetrical for stretch and release stimuli. Thus, these motor neurons are the decisive rectifiers for the extensor part of the femurtibia control loop. The habituation of FETi during repetitive stimulation is produced by a decrease in response amplitude together with a hyperpolarizing dc-shift. The imput of both neurons behaves like the output of a lead-lag-system with a predominant phasic component, whose high-pass filter has a time constant which depends on input slope. The nonlinear high-pass filter properties which are one important cause of catalepsy can thus be attributed to properties of interneurons and/or chordotonal organ. For most parts of the simulation of the femur-tibia control system (Cruse and Storrer, 1977) the anatomical and physiological correlates could be shown (Fig. 13).