Frequency-intensity characteristics of cricket cereal interneurons: broadband units

The bilateral pairs of cercal interneurons 10-2a and 10-3a in the cricket t erminal ganglion are supposed to constitute a functional system for measuri ng the direction of air-borne signals, based on their phase-locked response s and selective directional sensitivity. The purpose of this study was to o btain information on the frequency and intensity characteristics and thus t he potential working range of this system. By recording intracellularly fro m the axons of the interneurons we measured responses for stimuli of varyin g frequency, intensity, and direction. Typically, the stimulus frequency ra nge examined extended from 5 to 600 Hz, at intensities of 0.03-30 mm s(-1) (peak-to-peak air-particle velocity). The results show that interneurons 10 -2a and 10-3a preserved their level of activity, response type, and directi on tuning in the whole frequency range tested. Stimulus-response cross-corr elograms revealed that spike trains were synchronized with stimulus waves a t even higher frequencies, at least up to 1000 Hz. At a given air-particle velocity in the range of about 2-2.5 logarithmic units, the spike number re sponses of the interneurons were nearly constant over a wide frequency rang e. Directional diagrams appeared to be independent of stimulus frequency, b oth in orientation and in amplitude.