Comparative auditory neurophysiology of the inferior colliculus of two molossid bats,molossus ater andmolossus molossus
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Recordings were made from single inferior colliculus neurons of two closely related bat species,Molossus ater andMolossus molossus, both emitting short CF-FM echolocation calls which differ only in frequency range. Employing pure tone stimuli, minimum thresholds, tuning curves, response patterns and spike count functions were measured and compared between the two species.
The audiograms (evoked potential measurements and distribution of single neuron thresholds) of both species are rather broadly tuned, but maximum auditory sensitivity is reached at different frequency ranges according to the different spectral content of the orientation calls.
Single unit data concerning tuning curves, Q10dB-values, response patterns and spike count functions are very similar in the samples obtained from the two molossid species and closely resemble data from bats using FM-orientation calls.
The inferior colliculus of molossids is tonotopically organized. Asymmetrical and symmetrical tuning curves were found. Q10dB-values rarely exceeded 20, and so are values known as characteristic for other mammals. The dominant response pattern class is the “phasic-on” type with no or low spontaneous activity. Spike count functions of the non-monotonic type prevail.
Data are compared with results from “long CF-FM-bats”, revealing striking species differences in frequency selectivity of single neurons and organization of the ascending auditory pathway. This suggests different strategies in information processing which are discussed as adaptations to the species specific orientation calls.
KeywordsResponse Pattern Single Neuron Inferior Colliculus Tuning Curve Tone Stimulus
sound pressure level re. 0.00002 N · m−2
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