Transcript Cochlear implants

Cochlear Implants
The cochlear implant is the most significant technical
advance in the treatment of hearing impairment since
the development of the hearing aid around the turn of
the century.
Designed to restore some sense of hearing for:
• Children or adults who receive little or no benefit
from hearing aids.
• Loss must be: (a) profound, (b) bilateral, and (c)
sensorineural (sensory but not neural is more
accurate).
• Problem: Auditory nerve is intact, but hair cell
transducers are not functioning.
Purpose of implant: Generate
electrical signals that do the job that
is normally carried out by the
damaged hair cells.
Normal Ear
Deafness
Dorman (2004)
Normally
functioning hair
cells damaged or
not present; there
is some atrophy of
8th N dendrites in
most cases.
Transmitting Coil
Receiving Coil
Electrode Array
Note: There is also a speech processor, which is not
shown in this picture.
Speech Processor
The speech processor uses a
bank of bandpass filters (or
a Fourier analyzer) to
separate the signal into some
number of frequency bands
(e.g., 22) before passing it
along to the array of
electrodes.
What part of the auditory
system is the speech
processor replacing?
Speech Processor
(Note: CI users may actually
have two eyes.)
Dorman (2004)
Several speech processor designs are in use. This figure
shows a simplified version of a common processor design.
http://medimoon.com/2014/05/children-with-cochlear-implants-at-risk-for-deficits-in-executive-function/
https://www.boystownhospital.org/patientServices/Pages/CochlearImplantCenter.aspx
http://advancingyourhealth.org/highlights/2014/08/27/cochlear-implants-hearing-loss/
http://infanthearing.vihsp.org.au/following-diagnosis/cochlear-implants
CI user with a diagram showing (roughly)
what things look like on the other side of the
skull.
http://www.pddcs.co.uk/2012/07/what-does-cochlear-implant-look-like-in.html
Brief Digression
1. In the U.S. the largest population of CI users
consist of:
a. children
b. Adults
2. Most deaf adults are:
a. prelingually deaf
b. postlingually deaf
NIH Publication No. 11-4798 (2013-11-01). "Cochlear Implants". National Institute on Deafness and Other
Communication Disorders. "According to the Food and Drug Administration (FDA), as of December 2012,
approximately 324,200 people worldwide have received implants. In the United States, roughly 58,000 adults and
38,000 children have received them."
This figure shows which electrodes are receiving the most
electrical current for some sample speech sounds for a 22electrode implant.
(Note that electrode 1 stimulates the basal end and
electrode 22 stimulates the apical end.)
base →
Frequency →
F2&F3
apex →
↓
F1&F2 →
voicing →
F1
↓
Notice that these electrode stimulation patterns resemble
spectrograms, with two exceptions: (1) only a single time
slice for each sound is shown (these patterns will extend for 100 ms
or more in connected speech) , and (2) with only 22 channels, the
frequency resolution is not nearly as good as you would see
in a spectrogram.
base →
Frequency →
F2&F3
apex →
↓
F1&F2 →
voicing →
F1
↓
1 ch
2 ch
3 ch
4 ch
6 ch
8 ch
music
(orig)
GOOD NEWS, BAD NEWS
First the Bad News
• Implant based primarily on place theory. If we
make the most generous assumption that place
theory is correct (it is probably incomplete), how
many stimulating electrodes should there be?
• The CI restores some sense of hearing, but it is
nowhere near the hearing sensation that is
produced in a normal ear. (There are no “bionic
parts” that work as well as the original.)
• Subjects vary wildly in the amount of benefit they
derive from a CI -- mostly for unknown reasons.
Now the Good News
Despite these drawbacks, CIs work. Research shows:
• Ability to understand speech improves.
• Children acquire speech and language skills more
quickly.
• Post-lingually deafened adults maintain their
speech production skills better – especially control
of pitch and loudness, which improves
immediately most of the time.
Addendum: How the Implant
Works: The Standard Story
This explanation obviously requires that 8th N
dendrites be present. Are they?
A postmortem study * of 16 temporal bones from CI
patients showed that some had very few dendrites and
most had none. None.
How do you get tonotopic organization out of a system
like this in which the full bundle of 8th N cell bodies is
stimulated all at once rather than in a location-specific
way?
*Linthicum
FH, Fayad J, Otto SR, Galey FR, House WF (1991). "Cochlear Implant Histopathology,"
Am J Otol 12 No 4 1991 245-311.