PERIPHERAL MECHANISM OF HEARING IN LOCUST

Abstract

1. The tympanic organ of L. migratoria danica was found to accept well even the ultrasonic waves. The response frequency range was from 0.6 to 45 kcps, the most sensitive frequency range being from 5 to 9 kcps.2. The mode of conveying the information of the tympanic neuron to the central nervous system was found as follows:A. The tympanic neuron sent impulses in the pattern of slow adaptation and did not discharge synchronously with the sound frequency as seen on cereal hair sensilla. The relations bdtween the number of spikes per second and the intensity of sound in decibel unit were sigmoid and almost parallel to one another for different sound frequencies A neuron responded with the highest rate of spike discharges to the sound to which the neuron was most sensitive.B. The largest response area of single tympanic neuron almost covered the threshold curve of the whole tympanic organ and the characteristic frequency of each neuron was almost the same. From those facts it was concluded that in the tympanic organ there was no neuron which had a biased response area and therefore the tympanic organ might not have the ability of analyzing the sound frequency.3. The slow potentials were recorded from the chordotonal organ. They were divided into four types: negative monophasic, negative-positive diphasic, positive monophasic with an abrupt rise and fall, and also that with a slow rise and fall.4. The slow potential changed as if it were the envelope of the sound wave and was almost nonadaptive to prolonged sounds. The relation between its amplitude and the intensity of sound in decibel unit was measured.5. When a prolonged and a short sound were delivered simultaneously, the slow potential evoked by the short sound superimposed on the long lasting one evoked by the prolonged sound. When the response to the prolonged sound was nearly saturated in amplitude, the response to the short sound delivered simultaneously was almost undiscernible.6. Positive spikes superimposed on the rising phase of the positive slow potential. By weakening of the stimulus sound, a number of spikes decreased with the slow potential, until only the slow potential remained there.7. It was discussed that the slow potential change obtained from the tympanic organ might be the so-called generator potential of this organ. Such a potential change as the microphonics was not obtained from the tympanic organ unlike the cochlea of higher animals, although the functions of both organs are the same.