Abstract
Echolocating bats assess target range by the delay in echo relative to the emitted sonar pulse. Earlier studies in FM bats showed that a population of neurons in auditory centers above the inferior colliculus (IC) is tuned to echo delay, with different neurons tuned to different echo delays. A building block for delay-tuned responses is paradoxical latency shift (PLS), featuring longer response latencies to more intense sounds. PLS is first created in the IC, where neurons exhibit unit-specific quantum increase in response latency with increasing sound level. Other IC neurons display oscillatory discharges whose period is unit-specific and level tolerant, indicating that this is attributable to cell’s intrinsic properties. High-threshold inhibition of oscillatory discharge produces PLS, indicating that oscillatory discharge is a building block for PLS. To investigate the cellular basis of oscillatory discharges, we performed whole-cell patch-clamp recordings from IC neurons in leopard frogs (which also exhibit oscillatory discharges and PLS). These recordings show that IC neurons are heterogeneous displaying diverse biophysical phenotypes; each phenotype (and cell) has its own membrane time constant, input resistance, and strengths of I h, I kir, I kv—these intrinsic properties give rise to cell-specific resonance which can be observed through current and afferent stimulations.
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Abbreviations
- CF:
-
Constant-frequency
- IC:
-
Inferior colliculus
- FM:
-
Frequency-modulation
- FP:
-
Frequency preference
- GABA:
-
Gamma amino butyric acid
- PLS:
-
Paradoxical latency shift
- SPL:
-
Sound pressure level
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Acknowledgments
This research was supported by grants (R01DC00663, R01DC01951, R01DC04998) from the National Institute for Deafness and Other Communication Disorders of the NIH. Alex Galazyuk, Daniel Llano, Wenyu Lin and Sungchil Yang made major contributions towards the body of work described in this review paper. I thank two anonymous reviewers for their constructive criticisms on an earlier version of this manuscript.
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Feng, A.S. Neural mechanisms of target ranging in FM bats: physiological evidence from bats and frogs. J Comp Physiol A 197, 595–603 (2011). https://doi.org/10.1007/s00359-010-0533-5
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DOI: https://doi.org/10.1007/s00359-010-0533-5