Elsevier

Hearing Research

Volume 79, Issues 1–2, September 1994, Pages 105-114
Hearing Research

Responses of inferior collicular neurons of the FM bat, Eptesicus fuscus, to pulse trains with varied pulse amplitudes

https://doi.org/10.1016/0378-5955(94)90132-5Get rights and content

Abstract

Under free field stimulation conditions, we studied the responses of inferior collicular neurons of the FM bat, Eptesicusfuscus, to pulse trains with varied pulse amplitudes. Each pulse train consisted of 7 pulses of 4 ms delivered at 24 ms interpulse-intervals (i.e. 42 pulses/s). For a control pulse train, all pulse amplitudes were equal to a neuron's best amplitude which, when delivered in single pulses, elicited maximal number of impulses from the neuron. The amplitudes of individual pulses of the remaining pulse trains were linearly increased or decreased at a slope of 0, 14, 28, 42, 56 and 69 dB/s. All 56 inferior collicular neurons discharged to pulse trains were of two main types. Type I (N43, 77%) neurons discharged to each pulse within a train while type II (N11, 20%) neurons discharged to the first pulse of a train stimulus only. Discharge patterns of the remaining (N2, 3%) neurons changed between type I and type II when stimulated with different pulse trains. The number of impulses discharged by a neuron varied with different pulse trains. In addition, the number of impulses discharged to each pulse by type I neurons also varied among individual pulses within the train. Only 14 neurons (25%) discharged maximally to the control pulse train. Responses of the remaining neurons to other pulse trains were either 30%–120% larger than (N17, 30%) or within 30% (N25, 45%) of the control pulse train response. Furthermore, half of 56 neurons selectively discharged to a most preferred pulse train with a response magnitude which was at least 50% larger than the response to the least preferred pulse train. Possible mechanisms underlying the different discharge patterns are discussed in terms of a neuron's recovery cycle, minimum threshold and inhibitory period relative to the temporal characteristics (pulse repetition rate and amplitude) of the pulse trains.

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    1

    Permanent address: Department of Neurophysiology, Tokyo Medical and Dental University, Japan.

    2

    Permanent address: Department of Physiology, Chang Gung Medical College, Taiwan, Republic of China.

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