Neural Mechanism of Hearing in Insects

Abstract

1. The frequency response ranges of the tympanal and cercal nerve were measured in ten species belonging to four families, Cicadidae, Acridiidae, Tettigoniidae and Gryllidae. The tympanal organs of Acridiidae and Tettigoniidae responded to ultrasonic waves and the most effective frequency was very high (> 10 kc./s.), while the response ranges of the other two families, Cicadidae and Gryllidae, were within that of man. The response ranges of the cercal nerves (lower) and tympanal nerves (higher) were partly overlapping. 2. Stridulation consisted of pulsatory sounds and had species-specific rhythms, to which the tympanal nerves responded with synchronous discharge. 3. The dominant frequency range involved in stridulation agreed well with the frequency range to which the tympanal organ of the same insect was most sensitive. 4. The threshold of the tympanal nerve varied with different directions of incident sound, especially for ultrasonic waves, indicating the possibility of directional sense. 5. Tympanal neurons of Gampsocleis buergeri were referable to two types having different response ranges. 6. The curves relating number of spikes per second to intensity of stimulus were sigmoid and almost parallel for different frequencies. 7. In Discussion it is pointed out that although no single receptor organ is able to discriminate stimulus frequency, an insect which has different sound receptors on various parts of its body may have some power of discrimination.