Download auditory pathway

Reverberations in the Auditory System,
(Or: On theoretical models and on various
experimental data…)
Petr Marsalek
Prague, CZ, Charles University,
Medical Faculty 1, Institute of Pathological Physiology
Internal Seminar, Biological Physics @ MPI PKS
March 13, 2017
1 _
outline
1 brief review of hearing, from hair cells to the auditory pathway
2 spikes (discharges, action potentials) and post-synaptic
potentials are unitary neuronal events
3 experimental observations
4 sound localization circuits and their models
5 high frequency circuit (LSO) model and perspectives of how the
low frequency circuit (MSO) model can be described and
constructed
6 some computations with post-synaptic potentials
7 conclusions.
2 of X
outer, middle and inner ear
inner ear
middle ear
outer ear
3
[textbook]
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outer ear
outer ear
mechanical model
scaling factor?
1:10.. 1:20
[artifact]
4
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middle ear with small ear bones
levering impedance from air -> water
distance indicator
[artifact]
hammer
ear drum
stirrup
anvil
middle ear
mechanical model
scaling factor?
1:10.. 1:20
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inner ear (= cochlea) is enclosed in osseous
helical and spiral spatial tunnel (like snail shell)
Width at the base
100 mm
Length
33 mm
Width at the apex
500 mm
basilar membrane – from above and unfolded into
trapezoid plane, has graded stiffness
[textbook]
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cochlear cross section, hair cells, auditory nerve.
organ of Corti is active, mechanical-electrical transducer.
[textbook]
7 /~X
Inner Hair Cell
initiates spikes on the auditory nerve.
[textbook/ Bures thesis]
8
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High, Middle and Low
Spontaneous Rate
auditory nerve fibers
dB SPL,
decibel of sound pressure level
is objective unit of sound intensity
x-axis: stimulus intensity, dB SPL,
y-axis: neuronal spike rate per s
[Winter and Palmer, 1991]
WINTER I.M., PALMER A.R.
Intensity coding in lowfrequency auditory-nerve
fibers of the guinea pig.
J Acoust Soc Am. 1991, 90,
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pp. 1958–1967
auditory nerve
time histogram
x-axis: time; y-axis: neuronal characteristic frequency;
z-axis: spike time histogram
[Kiang, 1965]
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auditory nerve
interval histogram
x-axis: time, ms;
y-axis: Number of spikes
(A) stimulation frequency 412 Hz;
(B) stimulation frequency 1 kHz.
[Rose JE, 1962]
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x-axis: time,
y-axis: position along cochlea
[textbook]
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tonotopic organization of human auditory pathway
sound frequency, y-axis: gains of individual neurons;
filter bank x-axis:
Its granularity is one quarter of octave (multiples of \sqrt[4]{2})
cochlea and f = 128, 152, 181, 215, 256, 304, 362, 430, 512, ..., 8192 Hz,
these steps are critical bands, shown e.g. by masking
auditory nerve
10
0
-10
-20
-30
-40
-50
-60
-70
1
10
2
3
10
10
f
4
10
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x-axis, sound frequency (Hz), y-axis, sound pressure (Pa). Red top curve is pain
threshold. Hearing threshold is Green bottom curve (=normal audiogram). Blue are
curves of subjectively equivalent loudness level. Phon is its unit, like dB SPL. Yellow
blob is speech region. Gray line is reference frequency 1 kHz.
[textbook]
14
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Signal discrimination by ideal observer
x-axis: firing rates;
y-axis: response probabilities;
different signals are detected based on
variable responses and different mean
values
[reviews/ textbook]
15
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[reviews/ textbook]
auditory pathway
sound localization pathways
ITD and ILD
(interaural time and level
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differences)
XZ
WA
W AB
WB
0
2
4
6
8
10
time [ms]
XZ
WA
W AB
WB
0
1
2
3
4
5
6
7
8
9
top left: candidate
mechanisms of sound
azimuth in high
frequencies.
JND, just noticeable
difference in ILD, interaural level difference
can be equivalently
expressed in dB, or in
spikes/ s.
right column: shows
parameter variation.
10
time [ms]
[Bures and Marsalek]
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candidate mechanisms
of calculating sound
azimuth in low
frequencies with the use
of adding excitatory and
inhibitory postsynaptic
potentials
[Toth and Marsalek]
18
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solution to some
questions can be simple:
to calculate a “read-out”
curve, it takes to take
inversion function of a
spike time histogram, pick
a proper branch and a
proper function
normalization
[Toth and Marsalek]
19
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low frequency localization with
several different parameter
settings/ ideal observer readouts:
left: single neuron, unlimited time
right: reaction time TA, spike
timing jitter TJ, window of
coincidence detection wCD
[Sanda and Marsalek]
20
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Applications of auditory nerve spike train
studies: cochlear implants.
Some of subjects with cochlear implants (CI)
have both sides (mostly German speaking
countries :-). How is it with binaural hearing
and horizontal localization?
In tonal languages (Asian, eg. Chinese)
major CI are not useful. How can be pitch
impression restored?
In digital sound engineering, in normal
hearing, impression can be improved and/or
enhanced: viz surround sound…
ETC.
open problems,
interdisciplinary
questions,
technology
questions
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[inner ear and stato-kinetic organ]
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TOTH P.G. and MARSALEK P., Analytical description of
coincidence detection synaptic mechanisms in the auditory
pathway. Biosystems, 136, 90-98, 2015.
BURES Z. and MARSALEK P., On the precision of neural
computation with inter-aural level differences in the lateral
superior olive. Brain Res., 1536, 16-26, 2013.
SANDA P. and MARSALEK, P., Stochastic interpolation model
of the medial superior olive neural circuit, Brain Res., 1434,
257-265, 2012.
BURES Z., PhD thesis, 2007.
[References]
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