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Binaural Hearing: Lessons from Evolution

Binaural Hearing: Lessons from Evolution . Conference on Neural Dynamics and Computation in honor of John Rinzel NYU Courant Institute June 2009. Tetrapod auditory systems evolved in parallel. Sphenodontidae. Mammalia. Gymno-phiona. Aves. Testudines. Anura. Squamata. Crocodilia.

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Binaural Hearing: Lessons from Evolution

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  1. Binaural Hearing: Lessons from Evolution Conference on Neural Dynamics and Computation in honor of John Rinzel NYU Courant Institute June 2009

  2. Tetrapod auditory systems evolved in parallel Sphenodontidae Mammalia Gymno-phiona Aves Testudines Anura Squamata Crocodilia Urodela Quaternary 1.8 Cenozoic Tertiary Plesiosauria Ptero-sauria Ichthyo-sauria Dinosauria 65 Cretaceous 146 Mesozoic Jurassic 208 Triassic 250 Thecodontia Permian Therapsida “Stem reptiles” 290 Pelycosauria Carboniferous Paleozoic Early amphibians 360 Modified from Grothe, Nat. Rev. Neurosci, 2003 Devonian Rhipidistia 410 Sensitive, high-frequency hearing of airborne sound may be a recent event in vertebrate evolution

  3. Hearing of airborne sound evolved multiple times - in parallel • Each groups should be regarded as an independent experiment in hearing • Current theories suggest that there are major differences between directional hearing in bird and mammal brainstem • Compare with circuits for directional hearing in lizards • Identify computational principles underlying sound localization

  4. A circuit for detection of interaural time differences (ITD) • Delay line inputs synapse on coincidence detector neurons • These neurons compute the new variable, ITD, and transform the time code into a place code Jeffress model

  5. ITD detection circuits in the barn owl conform to the Jeffress model IPSI NM neurons project bilaterally to NL to form maps of ITD CONTRA

  6. NL act as coincidence detectors Sound signals from left & right ears converge through the two prominent dendrites From Macleod, 2007 From Ashida, 2007

  7. Similar (not identical) circuits in mammals • Neurons in MSO act as coincidence detectors • But do the inputs form a map of ITD? • Currently debated

  8. Does ITD coding require a map? • Harper and McAlpine (2004) proposed optimal coding strategy for ITD depends on head size. • Test their predictions in the chicken

  9. Good enough solutions ? • Gerbils may have a population rate code rather than a map. • birds a ‘labeled line’ population code Diagrams from Grothe and Köppl

  10. Can evolutionary history explain the differences? Aves Crocodilia • How did ITD circuits evolve? • Compare with other birds and alligators • Do ITD computations constrain map formation? Ptero-sauria Dinosauria

  11. computational principles in the auditory system • Computing source location is evolutionarily important • Birds, crocodilians and mammals use parallel coding strategies • Lizards have another solution • sound location circuits highlight evolutionary constraints in circuit design and coding

  12. Binaural Hearing: Lessons from Evolution • And at the same time tomorrow… • Stay tuned for Leo van Hemmen’s talk • Theory of internally coupled ears – the ICE model: How lizards and birds provide us with a novel category of hearing

  13. Thanks, John !

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