The effect of sound intensity on duration-tuning characteristics of bat inferior collicular neurons.
Previous studies have shown that inferior collicular neurons of the big brown bat, Eptesicus fuscus, serve as short-, band-, long- and all-pass filters for sound durations. Neurons with band-, short- and long-pass filtering characteristics discharged maximally to a specific sound duration or a range of sound durations. In contrast, neurons with all-pass filtering characteristics do not have duration selectivity. To determine if duration-tuning characteristics of collicular neurons were tolerant to changes in sound intensity, we examined the duration-tuning characteristics of collicular neurons using a wide range of sound intensities. Duration-tuning characteristics examined included the type, bandwidth and slope of duration-tuning curves. Sound intensity delivered within 20 dB of minimum threshold did not affect duration-tuning characteristics of all collicular neurons studied. Sound intensities at still higher levels did not affect the tuning characteristics of two-thirds of collicular neurons but decreased the duration selectivity and changed the duration-tuning curves of the remaining one-third of neurons from one type to another. However, these two groups of duration-tuning collicular neurons were not separately organized inside the inferior colliculus. The biological relevance of these findings to bat echolocation is discussed.
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Division of Biological Sciences, University of Missouri-Columbia, 65211, USA. jenp@missouri.edu
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D000161:Acoustic Stimulation; D000200:Action Potentials / Q000502:physiology; D000818:Animals; D002685:Chiroptera / Q000502:physiology*; D004455:Echolocation / Q000502:physiology*; D004567:Electrodes, Implanted; D007245:Inferior Colliculi / Q000166:cytology / Q000502:physiology*; D009474:Neurons / Q000502:physiology*