Analysis of the cricket auditory system by acoustic stimulation using a closed sound field

Abstract

A closed sound field system for independent stimulation of both cricket hearing organs is described. The system was used to measure acoustic parameters of the peripheral auditory system inGryllus campestris and to analyze inhibitory responses of the omega cell, a segmental auditory interneuron in the prothoracic ganglion. 1. Best sound transmission in the tracheal pathway occurs at 5 kHz. Closing of the prothoracic spiracles results in increased sound transmission but does not influence the frequency of best transmission in most animals (Fig. 6 B). Sound transmission is modulated by abdominal contractions associated with the respiratory cycle (Fig. 7). 2. AttenuationΔ and phase shift ϕ in the tracheal pathway have been determined for the frequency range of 2 to 10 kHz in animals with closed spiracles.Δ shows a minimum at 5 kHz and ϕ increases almost linearly with frequency (Fig. 11). 3. Sound components acting on each side of the large tympanal membrane form a resultant sound pressure based on linear superposition. This resultant sound pressure represents the effective stimulus of the auditory sense organ (Fig. 12). 4. The response of the omega cell is dependent upon both intensity and relative phase of sound signals applied to the tympanal membranes (Fig. 10). 5. At 5 kHz, the response of the omega cell decreases linearly with increasing contralateral (inhibitory) stimulus intensity over a wide range of intensities. The latency between stimulus onset and response is nearly independent of contralateral inhibition (Figs. 15 and 16). 6. Response (spike number) differences between an omega cell and its complementary mirror image cell due to different stimulus intensities at both ears are enhanced by the neuronal mechanism of contralateral inhibition. In one animal the gain in spike number difference at 5 kHz was calculated to be 60% relative to the response difference when contralateral inhibition was disabled. 7. Evidence for a low frequency (f≦2 kHz) ipsilateral inhibition of the omega cell is presented (Fig. 17).