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

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

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

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

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 McAlpine (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? How did ITD circuits evolve? Compare with other birds and alligators Do ITD computations constrain map formation? Dinosauria Ptero- sauria Aves Crocodilia

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 !