INFORMATION-PROCESSING IN THE FEMUR-TIBIA CONTROL LOOP OF STICK INSECTS .1. THE RESPONSE CHARACTERISTICS OF 2 NONSPIKING INTERNEURONS RESULT FRONT PARALLEL EXCITATORY AND INHIBITORY INPUTS

The complicated response characteristics of the identified nonspiking interneuron type E4 upon elongation stimuli to the femoral chordotonal organ (fCO) can be obtained by a computer simulation using the neuron al network simulator BioSim, if the following assumptions were introdu ced: (1) The interneurons receive direct excitatory input from positio n- and velocity-sensitive fCO afferents but also, in parallel delayed inhibition from the same velocity-sensitive afferents. (2) Position-se nsitive afferents in part show adaptation with a rather long time-cons tant. A subsequent experimental analysis demonstrated that all these a ssumptions fit the reality: (1) Interneurons of type E4 receive direct excitatory input from fCO afferents. (2) Interneurons of type E4 are affected by velocity dependent delayed inhibitory inputs from the fCO. (3) The fCO does contain adapting position-sensitive sensory neurons, which have not been described before. The described principle of the information processing is also able to generate the response in intern eurons of type E6 with less steep amplitude-velocity characteristic du e to a different weighting of the direct excitation and delayed inhibi tion.