Auditory response of saccular neurons of the catfish,Ictalurus punctatus

Abstract

1. Single unit recordings were made from neurons in the saccular branch of the eighth nerve in the catfish,Ictalurus punctatus. Spontaneous activity varied from zero to 184 spikes/s among the units recorded. Non-spontaneous units and three types of spontaneous activity were observed including regular, irregular and bursting. Non-spontaneous units were most frequently encountered. 2. Iso-intensity curves were used to examine the frequency response areas of the neurons. The best frequencies of different units were continuously distributed from below 160 Hz to over 1,250 Hz, with the most abundant units exhibiting best frequencies below 250 Hz. 3. Units having different best frequencies were, to a limited extent, tonotopically distributed within the saccular nerve, with low frequency units located more dorsally in the nerve than the high frequency units. 4. Phase locking was quantitatively assessed using a coefficient of synchronization (R). For each unit, the degree of phase locking varied with frequency and intensity of the stimulus. At any one intensity, the highest degree of phase locking was generally observed at the unit's best frequency. Increases in stimulus intensity resulted in enhanced phase locking ability up to a maximum value. The maximum R value was lower for units having best frequencies above 630 Hz, suggesting that these units were less capable of phase locking than lower frequency units.