Cochlear Implants
Ryan S. Clement, PhD
Neural Engineering and Applications Laboratory
BioE 200: September 18, 2002
Anatomy and Physiology of
Hearing
External Ear
Middle Ear Bones
Cochlea
Ear Canal
Ear Drum
Adapted from: http://funsan.biomed.mcgill.ca/~funnell/AudiLab/501/mmem003.html
Anatomy and Physiology (con’t)
Cochlear Cross-section
http://shark.me.nus.edu.sg/~asme/MechHear.htm
Traveling Wave Movie
©Howard Hughes Medical Institute
http://www.iurc.montp.inserm.fr/cric/audition/
Sound Transduction
Cochlea Hair Cells
Cochlear cross-section (single turn)
Auditory Nerve
Basilar Membrane
http://www.iurc.montp.inserm.fr/cric/audition/
Sensorineural Hearing Loss
OHCs
IHCs
• Causes
–
–
–
–
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Microscopic
view of hair
cells.
Heredity
Genetic
Aging process
Ototoxic drugs
Excessive
exposure to loud
sounds
Electrical Stimulation Can Allow
Us to Bypass Damaged Haircells
A Brief History
• Volta (1790)
– metal rods and battery induced sounds like boiling
liquid!
• Djourno and Eyries (1957)
– First demonstration of direct electrical stimulation of
auditory nerve
• House and Urban (1972)
– Develop and test first prototype (single channel)
– House/3M device gets FDA approval in 1984
A Brief History (con’t)
• Clark, University of Melborne (1978)
– Implant first multi-channel device
– FDA approval in 1985
• From then till now:
– continual improvements have been made in
speech processing strategies and electrode
design
– Many patients can use the devices without the
aid of lip-reading (even the telephone!)
Safety Considerations
• Biomaterials:
• with the proper choice of materials there is no infection, just a minor
fibrous sheath around the implant.
• Electrode Insertion trauma:
• factors: surgical technique, dimensions, array’s mechanical properties
• If damage occurs to basilar membrane and dendrites, could lead to
retrograde deterioration. However, are few and far between in most
sensorineural hearing loss cases.
• For most part damage is minimal.
• Chronic Electrical Stimulation
• Platinum electrodes: virtually no corrosion or depletion
• Doesn’t destroy AN, in fact can help keep auditory nerve and cells in
cochlear nucleus healthy (Leake et al 1992)
• impedances and thresholds stabilize several days post implant
Current Facts About Cochlear
Implants
Quick Facts:
• candidacy: severe-to-profound
sensorineural deafness
Cochlear Corporation: NucleusTM
•~70,000 recipients worldwide
(~21,000 in the U.S.) *
• 50% children (12 mo-17 years); 50%
adults *
• Manufacturers:
FDA
approved
Cochlear Corporation: NucleusTM
Advanced Bionics: ClarionTM
Med-EL: Combi-40+TM
AllHear: AllHearTM single channel
Antwerp Bionic Systems: LauraTM (now
owned by Cochlear)
MXM Laboratories: DigisonicTM
* FDA survey of venders 11/2001
http://www.nidcd.nih.gov/health/pubs_hb/coch.htm#c
(The University of Melbourne)
• Company founded by Dr. House
http://www.allhear.com/
• Shorter insertion; claims to retain residual hearing in implanted ear
• Single stimulation channel
• Not yet approved for sale in United States
Cochlear Corporation
Speech Processors
Contour
• Company created out of Greame Clark’s work
at the University of Melbourne, Australia
• First FDA approved multichannel devices
• 22 channels available for stimulation
Advanced Bionics
The Clarion II Implant
• Based on work conducted at UCSF
• Only American Company
• 16 channels with 16 individual
current drivers
Med-El Corporation
Processors
Combi 40/40+ Implant
• Headquarters in Austria
• case for less signal loss and power
consumption
• 12 channels of stimulation
Block Diagram for Typical Cochlear Implant
System
Skin
Transmission
Link
mic
Speech
Proc.
Encoder
External Components
Receiver/
Decoder
Electrodes
AN and
Aud CNS
Internal Components
The Speech Signal
“Never touch a snake with your bare hands.”
Progression of Speech Processing
Strategies
Sound Input
Speech Processing
Electrical Stimulation
Cochlear Frequency Tuning
The cochlea is arranged such that
different regions of the cochlea
correspond to different pitches.
Multichannel cochlear implants take
advantage of this fact to encode
different frequencies in the speech
signal.
Cochlear Electrodes
Cochlear Corporation’s Nucleus Electrode
Cochlea
Cochlear
Electrode
Auditory
Nerve
What might cochlear implants
sound like?
• Cochlear implant simulations:
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–
–
–
–
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Single channel
2 channels
3 channels
4 channels
6 channels
8 channels
(created from Bob
Shannon and Philip
Lizou’s model)
Dorman 2002
Scores on NU6/CNC words
100
90
Percent Correct
80
70
60
50
40
30
20
10
0
Med El CIS-Link
Nucleus 22
Clarion v1.2
Nucleus 24
Clarion
Hi-Focus
C II
Hi Res.
Factors Effecting Cochlear
Implant Performance
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•
•
•
•
Duration of deafness
Age of onset of deafness
Age at implantation
Duration of cochlear implant use
Other:
– Number of remaining auditory nerve fibers
– Electrode placement and insertion depth
– Dynamic range
Future Research Directions
• Better understanding of fundamental
mechanisms
• Better speech processing algorithms
• Improved enjoyment of music
• Electrode design improvements
• Objective fitting for young children
• Aesthetics (smaller, totally implantable)
Cochlear Implant Research Team
• Requires integration of many disciplines:
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–
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–
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Bioengineering
Physiology
Otolaryngology
Speech Science
Signal Processing