Transcript CCarr-NDC-RINZEL-JUN-2009

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
GymnoSquamata
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
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? 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 !