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Processing amplitude-modulated sounds by the auditory midbrain of two species of toads: matched temporal filters

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Summary

  1. 1.

    Recordings were made from single units in the torus semicircularis ofBufo americanus andBufo fowleri. Using sinusoidally amplitude-modulated (AM) white noise as a stimulus, the temporal selectivity of these neurons could be described by five response categories: ‘AM nonselective’ (40%); ‘AM high-pass’ (8%); ‘AM low-pass’ (9%); ‘AM band-suppression’ (9%); and ‘AM tuned’ (34%).

  2. 2.

    The degree to which the stimulus modulation rate was coded in the periodicity of spiking of each toral neuron (i.e., synchronization of a unit's spikes to a particular phase of the modulation waveform) was calculated for modulation rates ranging from 10 to 150 Hz. The synchronization characteristics of toral neurons generally failed to reveal the temporal selectivity of these cells. In fact, those units which were most sharply AM-tuned rarely exhibited significant response synchronization at any modulation rate tested.

  3. 3.

    The distribution of ‘best rates of AM’ is different for the two species of toads; AM-tuned neurons recorded from the torus semicircularis of Fowler's toad were, on the average, tuned to higher rates, relative to those recorded from the American toad. These findings constitute positive evidence for the existence of ‘matched temporal filters’ in the anuran central auditory system.

  4. 4.

    Synthetic stimuli differing only in the rate at which they were amplitude modulated were used to evoke advertisement calls from maleBufo americanus. Modulation rates of 7.5 Hz, 15 Hz, 30 Hz, 60 Hz and 120 Hz were used. In these field studies males responded best to 30 Hz AM; lower or higher modulation rates were less effective. The AM-tuned neurons in the torus semicircularis of this species are well suited to process AM rates of 30 Hz.

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Abbreviations

AM :

amplitude modulated

BEF :

best excitatory frequency

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Author notes

  1. Gary J. Rose

    Present address: Neurobiology Unit, Scripps Institution of Oceanography, University of California at San Diego, 92093, La Jolla, CA, USA

Authors and Affiliations

  1. Section of Neurobiology and Behavior, Division of Biological Sciences, Cornell University, 14853, Ithaca, New York, USA

    Gary J. Rose & Robert R. Capranica

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  1. Gary J. Rose
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  2. Robert R. Capranica
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Rose, G.J., Capranica, R.R. Processing amplitude-modulated sounds by the auditory midbrain of two species of toads: matched temporal filters. J. Comp. Physiol. 154, 211–219 (1984). https://doi.org/10.1007/BF00604986

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