Identified auditory neurons in the cricket Gryllus rubens: temporal processing in calling song sensitive units

Abstract

This study characterizes aspects of the anatomy and physiology of auditory receptors and certain interneurons in the cricket Gryllus rubens. We identified an `L'-shaped ascending interneuron tuned to frequencies >15 kHz (57 dB SPL threshold at 20 kHz). Also identified were two intrasegmental `omega'-shaped interneurons that were broadly tuned to 3–65 kHz, with best sensitivity to frequencies of the male calling song (5 kHz, 52 dB SPL). The temporal sensitivity of units excited by calling song frequencies were measured using sinusoidally amplitude modulated stimuli that varied in both modulation rate and depth, parameters that vary with song propagation distance and the number of singing males. Omega cells responded like low-pass filters with a time constant of 42 ms. In contrast, receptors significantly coded modulation rates up to the maximum rate presented (85 Hz). Whereas omegas required ∼65% modulation depth at 45 Hz (calling song AM) to elicit significant synchrony coding, receptors tolerated a ∼50% reduction in modulation depth up to 85 Hz. These results suggest that omega cells in G. rubens might not play a role in detecting song modulation per se at increased distances from a singing male.