Cochlear Implants

Ryan S. Clement, PhDNeural Engineering and Applications Laboratory

BioE 200: September 18, 2002

Anatomy and Physiology of Hearing

External Ear

Ear Canal

Adapted from: http://funsan.biomed.mcgill.ca/~funnell/AudiLab/501/mmem003.html

Cochlea

Middle Ear Bones

Ear Drum

Anatomy and Physiology (con’t)

http://www.iurc.montp.inserm.fr/cric/audition/

Traveling Wave Movie

Cochlear Cross-section

http://shark.me.nus.edu.sg/~asme/MechHear.htm

cochleaWeb.mov

©Howard Hughes Medical Institute

Sound Transduction

Basilar MembraneAuditory Nerve

Cochlear cross-section (single turn)Cochlea Hair Cells

http://www.iurc.montp.inserm.fr/cric/audition/

Sensorineural Hearing Loss

• Causes– Heredity– Genetic– Aging process– Ototoxic drugs– Excessive

exposure to loud sounds

Microscopic view of hair cells.

OHCs

IHCs

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

(The University of Melbourne)

Current Facts About Cochlear Implants

Quick Facts:

• candidacy: severe-to-profound sensorineural deafness

•~70,000 recipients worldwide (~21,000 in the U.S.) *

• 50% children (12 mo-17 years); 50% adults *

• Manufacturers:Cochlear Corporation: NucleusTM

Advanced Bionics: ClarionTM

Med-EL: Combi-40+TM

AllHear: AllHearTM single channelAntwerp 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

Cochlear Corporation: NucleusTM

FDAapproved

• Company founded by Dr. House

• Shorter insertion; claims to retain residual hearing in implanted ear

• Single stimulation channel

• Not yet approved for sale in United States

http://www.allhear.com/

Cochlear Corporation

Contour

Speech Processors

• 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 BionicsThe Clarion II Implant

• Based on work conducted at UCSF

• Only American Company

• 16 channels with 16 individual current drivers

Med-El CorporationCombi 40/40+ Implant

• Headquarters in Austria

• case for less signal loss and power consumption

• 12 channels of stimulation

Processors

micSpeech

Proc.Encoder

Receiver/Decoder

ElectrodesAN and

Aud CNS

TransmissionLink

Block Diagram for Typical Cochlear Implant System

Skin

External Components Internal Components

The Speech Signal“Never touch a snake with your bare hands.”

Progression of Speech Processing Strategies

Speech ProcessingSound Input

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

CochlearElectrode

Cochlea

AuditoryNerve

Cochlear Corporation’s Nucleus Electrode

What might cochlear implants sound like?

• Cochlear implant simulations:– Single channel – 2 channels – 3 channels – 4 channels– 6 channels– 8 channels

(created from Bob Shannon and Philip Lizou’s model)

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Med El CIS-Link Nucleus 22 Clarion v1.2

Scores on NU6/CNC words

Nucleus 24 ClarionHi-Focus

C II Hi Res.

Per

cen

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orr

ect

Dorman 2002

Factors Effecting Cochlear Implant Performance

• 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:– Bioengineering– Physiology– Otolaryngology– Speech Science– Signal Processing