Labile cochlear tuning in the mustached bat |
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Authors: | Russell F Huffman O W Henson Jr |
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Institution: | (1) Curriculum in Neurobiology, The University of North Carolina, Chapel Hill, North Carolina, USA;(2) Department of Cell Biology and Anatomy, The University of North Carolina, Chapel Hill, North Carolina, USA;(3) Department of Neurobiology, Duke University Medical Center, Box 3209, 27710 Durham, NC, USA |
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Abstract: | Summary Acoustic stimuli near 60 kHz elicit pronounced resonance in the cochlea of the mustached bat (Pteronotus parnellii parnellii). The cochlear resonance frequency (CRF) is near the second harmonic, constant frequency (CF2) component of the bat's biosonar signals. Within narrow bands where CF2 and third harmonic (CF3) echoes are maintained, the cochlea has sharp tuning characteristics that are conserved throughout the central auditory system. The purpose of this study was to examine the effects of temperature-related shifts in the CRF on the tuning properties of neurons in the cochlear nucleus and inferior colliculus.Eighty-two single and multi-unit recordings were characterizedin 6 awake bats with chronically implanted cochlear microphonic electrodes. As the CRF changed with body temperature, the tuning curves of neurons sharply tuned to frequencies near the CF2 and CF3 shifted with the CRF in every case, yielding a change in the unit's best frequency. The results show that cochlear tuning is labile in the mustached bat, and that this lability produces tonotopic shifts in the frequency response of central auditory neurons. Furthermore, results provide evidence of shifts in the frequency-to-place code within the sharply tuned CF2 and CF3 regions of the cochlea. In conjunction with the finding that biosonar emission frequency and the CRF shift concomitantly with temperature and flight, it is concluded that the adjustment of biosonar signals accommodates the shifts in cochlear and neural tuning that occur with active echolocation.Abbreviations BF
best frequency
- CF
characteristic frequency
- CF2, CF3
second and third harmonic, constant frequency components of the biosonar signal
- CM
cochlear microphonic
- CN
cochlear nucleus
- CRF
cochlear resonance frequency
- IC
inferior colliculus
- MT
minimum threshold
- OAE
otoacoustic emission
- Q10dB
BF (or CF) divided by the response bandwidth at 10 dB above MT |
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Keywords: | Cochlea Cochlear nucleus Inferior colliculus Tonotopy Pteronotus |
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