binaural hearing: lessons from evolution conference on neural dynamics and computation in honor of...
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Binaural Hearing: Lessons from Evolution
Conference on Neural Dynamics and Computation
in honor of John Rinzel
NYU Courant Institute June 2009
Cen
ozoi
cM
esoz
oic
Pal
eoz
oic
Quaternary
Tertiary
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
1.8
65
146
208
250
290
360
410
Rhipidistia
Early amphibians
“Stem reptiles”
DinosauriaPtero-sauria
Plesiosauria
Ichthyo-sauria
Thecodontia
SphenodontidaeTestudinesSquamataAnuraUrodela
Gymno-phiona
AvesCrocodilia
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?
DinosauriaPtero-sauria
AvesCrocodilia
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