An electrophysiological study of sound sensitive neurons in the 'primitive ear' of acheta domesticus

Crickets have two types of mechanisms for the reception of environmental sounds: (1)the tympanal organs in the two forelegs and (2) the freely articulated setal receptors on the abdominal ceri. The cereal setal receptors have hitherto received much less experimental attention as decoders of biologically significant sounds than have the tympano-receptors. In the present study the cereal auditory system of Acheta domesticus was examined electrophysiologically to determine its auditory frequency sensitivity, the tuning characteristics of individual units, and the synchronization between nerve impulses and stimulus frequency. Both pre- and postsynaptic units were examined in the fifth abdominal ganglion; several of the observed response patterns were compared with those of homologous cereal sensory neurons in Periplaneta americana. The results show that (1) A. domesticus possesses an elaborate array of cereal receptors which are highly sensitive to sounds, (2) the cereal setal receptors are more sensitive and numerous in the cricket than in the cockroach, and (3) the cereal auditory system can decode stimulus information by narrow tuning in individual cells and by synchronous discharge patterns; firing frequencies range up to 300 Hz in presynaptic sensory units and 60 Hz in the postsynaptic giants. The response patterns were related to the structure of the receptor and the behavioural adaptations of the insect.