Temperature and Frequency Dependent Conduction Mechanisms ...
Frequency representation Part 2 Development of mechanisms involved in frequency representation.
-
date post
21-Dec-2015 -
Category
Documents
-
view
217 -
download
0
Transcript of Frequency representation Part 2 Development of mechanisms involved in frequency representation.
![Page 1: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/1.jpg)
Frequency representation
Part 2
Development of mechanisms involved in frequency representation
![Page 2: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/2.jpg)
Summary of development of frequency representation Frequency discrimination and frequency resolution
are immature in humans at birth, at least at high frequencies
Frequency discrimination at high frequencies becomes mature at about the same time as frequency resolution, around 6 months
Frequency discrimination at low frequencies continues to mature to at least school age
What are possible auditory physiological bases of immaturity? Are there other explanations?
![Page 3: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/3.jpg)
Overview of lecture Cochlear development (prenatal events for
humans) Anatomy Physiology
Neural contributions to the development of frequency representation Frequency resolution Temporal code for frequency
![Page 4: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/4.jpg)
Development of the cochlea
Frequency resolution is established in the mature cochlea and the
nervous system maintains that fine frequency resolution
![Page 5: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/5.jpg)
Very early cochlear development
Qu
ickTim
e™
and
aTIF
F (
Uncom
pre
sse
d)
decom
pre
ssor
are
ne
ed
ed
to s
ee
this
pic
ture
.
From Crossin et al, 1984
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
![Page 6: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/6.jpg)
Timing of cochlear development events in humans
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
From Northern & Downs, 1991
![Page 7: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/7.jpg)
Morphological development of the cochlea
![Page 8: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/8.jpg)
Prenatal and postnatal development of the cochlea
![Page 9: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/9.jpg)
Developmental events happen first at the base, and progress apically
![Page 10: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/10.jpg)
Hair cell innervation
![Page 11: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/11.jpg)
Development of hair cell innervation
![Page 12: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/12.jpg)
Some potentially important developments Changes in basilar membrane stiffness and
other mechanical properties of the organ of Corti.
Differentiation and innervation of hair cells Development of the stria vascularis and
endocochlear potential.
![Page 13: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/13.jpg)
At the onset of cochlear function, sensitivity and frequency resolution are poor.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
![Page 14: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/14.jpg)
Frequency gradient in development of frequency resolution?
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
![Page 15: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/15.jpg)
Measuring cochlear frequency resolution using otoacoustic emissions
Frequency
f1 f2
Leve
l
Frequency
f1 f2
Leve
l
2f1-f2
Frequency
f1 f2
Leve
l
Frequency
f1 f2
Leve
l 2f1-f2suppressor
![Page 16: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/16.jpg)
Measuring cochlear frequency resolution using otoacoustic emissions
Suppressor frequency
Suppressor level to reduce emission by 3 dB
![Page 17: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/17.jpg)
Cochlear frequency resolution development in humans
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
![Page 18: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/18.jpg)
So if cochlear tuning is mature,why do 3-month-old infants have immature frequency resolution?
![Page 19: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/19.jpg)
You can have mature and immature tuning in neurons tuned to the same frequency
Tuning quality
Frequency
Cochlea
Auditory nerveSuperior olive
![Page 20: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/20.jpg)
Development of the end bulb of Held
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
![Page 21: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/21.jpg)
Development of neural tuning in human infants
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
![Page 22: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/22.jpg)
Sound frequency to which animals first respond
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
![Page 23: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/23.jpg)
A paradox in development
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
![Page 24: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/24.jpg)
Place code shift
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
![Page 25: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/25.jpg)
Place code shift at three frequencies
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
![Page 26: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/26.jpg)
Other observations about the place code shift Responses in the nervous system shift with
the responses in the cochlea. The shift occurs in mammals. If an animal is trained to respond to a
certain frequency early in life, they will act like they learned to respond to a lower frequency later in life.
![Page 27: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/27.jpg)
Possible causes of the place code shift Middle ear response Outer hair cells Basilar membrane stiffness
![Page 28: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/28.jpg)
Timing in humans?
Qu
ickTim
e™
an
d a
TIF
F (U
nco
mp
resse
d) d
ecom
pre
sso
rare
nee
de
d to
see th
is p
ictu
re.
![Page 29: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/29.jpg)
Development of the temporal code for frequency
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Phase locking takes longer to develop than frequency tuning.
Phase locking develops in the central nervous system later than at the periphery.
![Page 30: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/30.jpg)
Development of phase locking in humans
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
![Page 31: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/31.jpg)
Development of phase locking in humans
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
![Page 32: Frequency representation Part 2 Development of mechanisms involved in frequency representation.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d615503460f94a42b3e/html5/thumbnails/32.jpg)
Development of frequency representation: Conclusions Frequency resolution at the level of the cochlea is
mature prior to term birth, but at the level of the brainstem is still immature until about 6 months.
The cochlear map of frequency shifts during development; in humans this occurs prenatally.
The development of the temporal code for frequency has not been studied extensively, but there is some evidence that it may take longer to develop than the place code.