REPRESENTATION OF BEHAVIORALLY RELEVANT SOUND FREQUENCIES BY AUDITORYRECEPTORS IN THE CRICKET TELEOGRYLLUS-OCEANICUS

Teleogryllus oceanicus is particularly sensitive to two ranges of soun d frequency, one corresponding to intraspecific acoustical signals (4- 5 kHz) and the other to the echolocation cries of bats (25-50 kHz). We recorded summed responses of the auditory nerve to stimuli in these t wo ranges. Nerve responses consist of trains of compound action potent ials (CAPs), each produced by the summed activity of a number of recep tor neurons, The amplitude of the CAP is up to four times larger for s timuli at 4.5 kHz than for stimuli at 30 kHz, suggesting either that t he extracellular spikes produced by receptors that respond to 4.5 kHz are larger than those that respond to 30 kHz, or that receptors fire m ore synchronously in response to stimulation at 4.5 kHz, or that more receptors respond to stimulation at 4.5 kHz, Neither unit spike amplit ude nor conduction velocity (which is expected to vary with spike ampl itude) differs for the two frequencies, and the responses to 4.5 kHz a re not produced by more tightly synchronized receptor populations, as judged by CAP breadth. We conclude that more receptors respond to 4.5 kHz than to 30 kHz.