Binaural Hearing Lessons from Evolution Conference on Neural

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

Cenozoic Tetrapod auditory systems evolved in parallel Sphenodontidae Gymno. Squamata phiona Urodela Anura Quaternary Aves Testudines Crocodilia Mammalia 1. 8 Tertiary Plesiosauria Ichthyosauria 65 Pterosauria Dinosauria Mesozoic Cretaceous 146 Jurassic 208 Triassic 250 Thecodontia Paleozoic Permian Therapsida “Stem reptiles” 290 Pelycosauria Carboniferous Early amphibians 360 Devonian Rhipidistia Modified from Grothe, Nat. Rev. Neurosci, 2003 410 Sensitive, high-frequency hearing of airborne sound may be a recent event in vertebrate evolution

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

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

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

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

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

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

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

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

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

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

Thanks, John !