Multiple mechanisms shape selectivity for FM sweep rate and direction in the pallid bat inferior colliculus and auditory cortex |
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Authors: | Zoltan M Fuzessery Khaleel A Razak Anthony J Williams |
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Institution: | (1) Department 3166, Zoology and Physiology, University of Wyoming, 1000 E. University Ave, Laramie, WY 82071, USA;(2) Department of Psychology, University of California, Riverside, CA 92521, USA |
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Abstract: | The inferior colliculus and auditory cortex of the pallid bat contain a large percentage of neurons that are highly selective
for the direction and rate of the downward frequency modulated (FM) sweep of the bat’s echolocation pulse. Approximately 25%
of neurons tuned to the echolocation pulse respond exclusively to downward FM sweeps. This review focuses on the finding that
this selectivity is generated by multiple mechanisms that may act alone or in concert. In the inferior colliculus, selectivity
for sweep rate is shaped by at least three mechanisms: shortpass or bandpass tuning for signal duration, delayed high-frequency
inhibition that prevents responses to slow sweep rates, and asymmetrical facilitation that occurs only when two tones are
presented at appropriate delays. When acting alone, the three mechanisms can produce essentially identical rate selectivity.
Direction selectivity can be produced by two mechanisms: an early low-frequency inhibition that prevents responses to upward
sweeps, and the same asymmetrical two-tone inhibition that shapes rate tuning. All mechanisms except duration tuning are also
present in the auditory cortex. Discussion centers on whether these mechanisms are redundant or complementary. |
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