Lecture 1.1- Intro/Hx of CIs

Question 1

How does a CI work?

Answer 1

It bypasses the damaged peripheral hearing system and directly stimulates CN VIII.

Question 2

Do recipients of CIs always have SNHL?

Answer 2

Not necessarily a strict SNHL.

- Can be mixed or more neural (ANSD)

Question 3

What did Alessandro Volta discover?

Answer 3

Late 1790’s

• Described a “boom within the head” followed by a sound of “thick, boiling soup” after inserting 2 rods connected to a 50V electrical source into his ears

Question 4

What did Guillaume-Benjamin-Amand Duchenne discover?

Answer 4

1855

Studied how neural pathways can conduct electrical pulses.

He experimented with alternating current in his ear.

Described sensation of “fly’s wings beating between a pane of glass and a curtain.”

Question 5

What did Brenner discover?

Answer 5

1868

Used bipolar stimulation (one electrode in ear canal in saline and another in different location on body) in 1 subject.

Reported on effects of polarity, rate, and intensity of stimulus and placement of electrodes.

Reported that negative polarity stimuli produced better hearing and that correct electrode placement reduced negative side effects.

Question 6

What was discovered at the military medical academy in Leningrad in the 1930’s?

Answer 6

o Stimulating electrodes inserted into the middle ear of patients with and without ME structures
o Frequency of AC (alternating current) was varied and patients asked to describe the pitch (Fersuni & Volokhov, 1936)
o Pitch was no different for patients with or without ME structures

Question 7

Define electrophonic hearing.

Answer 7

Electrical stimulation of the Organ of Corti causes mechanical response= release of neurotransmitters from hair cells onto nerve VIII (Stevens & Jones, 1939)

Basiliar membrane moves in response to voltage changes.

Question 8

How does electrophonic hearing work?

Answer 8

o Tectorial membrane converts electrical signal into acoustic resulting in tonal pitch but at double the signal frequency
o Direct electrical activation of nerve CIII w/ steep loudness growth and occasional activation of nerve VIII
o The more direct electrical stimulation given to nerve VIII results in stimulation of nerve VII

Question 9

Define the cochlear microphonic.

Answer 9

Electrical potentials measured primarily from OHCs in cochlea in response to stimulus closely mirrored the stimulus (Wever and Brady, 1930)

Question 10

Why did the cochlear microphonic dismiss the “telephone theory” of hearing?

Answer 10

The stimulus is not passed down site to site to site, with information lost.

The cochlear microphonic closely mirrors the actual stimulus.

Question 11

What did Gersuni and Volokhov report?

Answer 11

1936

Hearing at different pitches arose from different rates of stimulation in electrical hearing.

Question 12

What did Homer Dudley crate in 1939?

Answer 12

Vocoder.

Basis for early speech processing strategies for multi-channel implants.

Take signal and modify it in some way to change the outcome at stimulation (not 1-to-1 transmission)

Question 13

What kind of research was conducted in the 1940’s and 1950’s?

Answer 13

Large amounts of research went into telephonic hearing.

Conclusion= deafness could not be completely corrected with wide-field electrical stimulation. Instead, more localized stimulation of auditory nerve fibers would be necessary.

Question 14

When was the first CI invented?

Answer 14

1950’s

Surgeon Lundberg directly stimulated auditory nerve in patient during neurosurgery.

He used sinusoidal current and patient reported hearing only noise.

Question 15

What work was done by Djourno and Eyries in 1957?

Answer 15

Conducted seminal work on direct auditory nerve stimulation with coil.

o First subject was a 57-year-old-man s/p bilateral cholesteatoma resection which resulted in deafness (nerve VIII) and facial paralysis (nerve VII). Surgery performed on 2/25/1957
o Patient underwent extensive therapy and was able to discriminate intensity differences well. Frequency perception was poor and speech perception non-existent
 Low frequencies: burlap tearing
 High frequencies: silk ripping
o Could appreciate environmental noises and single words, but could not understand speech
o Implant subsequently malfunctioned (twice) and Eyries and Djourno stopped working together

Question 16

Describe the CI created by William House, M. D., D. D. S.

Answer 16

• First patients implanted in January 1961 had a gold wire implanted through the round window and brought out through the skin
• All three attempts (2 patients) yielded patient perception of square-wave stimulus, but all three had to be removed secondary to biocompatibility concerns
• Required current for stimulus perception increased over the course of use for both patients

Question 17

Describe the CI created by F. Blair Simmons.

Answer 17

• Conducted intraoperative study in an 18 y/o patient, which indicated bipolar stimulation of a nerve VIII yielded auditory sensations and discrimination of different stimulus frequencies
• Two years later (1964), he implanted an electrical hearing device into the modiolus of a 60-year-old-man
• Follow-up psychophysical testing of the patient was difficult and Simmons was pessimistic about future electrical stimulation of nerve VIII yielding useful speech information
o Use of electrical hearing for communication was “less than 5%” likely and Stanford put off human experimentation until animal testing could be done
o Currently, modiolus is the target for CIs

Question 18

When was the multi-channel CI proposed?

Answer 18

Robin Michelson, M.D., had implanted several deaf patients with single-channel cochlear implants in 1960’s

• Found that patients could discriminate among different stimulation rates up to 600 Hz and differentiate between square and sinusoid wave
• Showed that IC neurons responded similarly in animals with destroyed hair cells and those with intact hair cells
• First proof that electrical hearing was stimulating auditory nerve and not electrophonic hearing
• Also demonstrated that in single electrode devices, periodicity pitch up to 600 Hz possible, but place coding impossible
• In order to convey speech signal, would need multi-channel implant
• Presented findings at American Otologic Society in 1973

Question 19

What is the Bilger report?

Answer 19

1975: 13 single-channel CI users (11 by House and 2 by Michelson) were studied in Pittsburgh
o Audiologic
o Vestibular
o Psychoacoustic

• First study that legitimized CI use

• Found that speech-reading scores were improved in all adults and that quality of life was significantly improved with minimal risk
o Still no open set speech recognition
o Voice production improved

Question 20

What is the House/3M device?

Answer 20

1972: House and Urban developed speech processor to accompany their single-channel device (3M)
• First on-market device
• Implanted approximately 1000 people with device between 1972 and 1980’s
• Age criteria lowered from 18 years to 2 years of age in 1980
• Received FDA approval for commercial marketing device in 1984

Question 21

When was the multi-channel CI created?

Answer 21

Late 1970s and early 1980s by Michelson and Graham Clark

• Improve safety and durability of electrode array
• Ultimately led to production of Clarion (AB) and Nucleus (Cochlear) devices currently on market

Question 22

When was MED-EL founded and when was it approved by the FDA?

Answer 22

“First developed” in 1875

Approved by FDA in 2001

Question 23

When was AB founded and when was it approved by the FDA?

Answer 23

Founded in 1993

Approved by FDA in 1996

Question 24

What is incidence?

Answer 24

Occurrence rate

Question 25

What is prevalence?

Answer 25

How common a condition is right now

Question 26

How does length of deafness impact candidacy?

Answer 26

Not officially part of the candidacy criteria.

However, length of deafness is an important consideration.

Question 27

How does deafness affect the entire peripheral auditory system?

Answer 27

If something is deprived at the level of the hair cells, the neural structures beyond the hair cells will be affected

Question 28

Why are spiral ganglion cells important for success with a CI?

Answer 28

Spiral ganglion cells innervate nerve VIII

The more spiral ganglion cells you have, the better the chance the implant will be successful.

Question 29

What is the survival of SGNs dependent on?

Answer 29

• Presence of sensory epithelium

- Support cells of Organ of Corti

Question 30

What happens after the loss of epithelium and suport cells?

Answer 30

o Unmyelinated parts of spiral ganglion in OoC degenerate rapidly
o More gradually, myelinated portions within osseous spiral lamina atrophy
o Cell bodies in Rosenthal’s canal degenerate

Question 31

Why do patients with Connexin 26 do really well?

Answer 31

They have a lot of SGNs

Question 32

Why does loss of HCs cause SGN degeneration?

Answer 32

o HCs and support cells in OoC are lost in SNHL
o HCs express neurotrophic factors
o Support cells express nerve growth factors

Question 33

What are pathologies that directly affect SGNs?

Answer 33

o Viral and bacterial labyrinthitis
o Mechanical trauma
o Disruption of cochlear vasculature
 More rapid degeneration of SGNs

Question 34

What is the rate of SGN degeneration?

Answer 34

• Normal SGN population (28,418 +/- 3,675)
• Peripheral processes usually more extensively damaged than central processes
• SGN damage follows pattern of OoC damage – basal turn > apical turn

Question 35

What etiologies cause the most SGN loss?

Answer 35

o Postnatal viral labyrinthitis
o Congenital/genetic deafness
o Bacterial meningitis

Question 36

What etiologies cause the least SGN loss?

Answer 36

o Aminoglycoside antibiotics
o Sudden, idiopathic loss
o Meniere’s Disease
 Have fluctuating hearing loss with periods of good hearing

Question 37

What process happens at the cochlear nucleus a a result of deafness?

Answer 37

• Changes to cells in CN secondary to deafness are largely atrophic
• See degeneration/weakening of the system

Once hearing is reintroduced, this process stopcs/

Question 38

What are the pathophysiological effects of deafness on the CN?

Answer 38

• Increased threshold for activation
• Smaller action potentials
• Shorter membrane time constants
• Smaller after-hyperpolarizations

Question 39

How does the CI work in the auditory pathway?

Answer 39

• Electrically depolarizes local populations of SGNs, initiating an action potential
• Implant does not sustain the signal after the AP is initiated
• Conduction of the signal after the SGNs is performed via normal physiology processes

Question 40

How does deafness impact the inferior colliculus?

Answer 40

• ICC receives input from contralateral ear

- After 1 year of deafness, no difference found between normal hearing and unilateral deafness

Question 41

What are changes to auditory cortex secondary to deafness dependent on?

Answer 41

• Severity of SNHL
• Unilateral or bilateral
• Developmental stage at time of HL

Question 42

What are morphological changes to AC following deafness?

Answer 42

• Loss of synapses with prolonged deprivation of auditory input
• In the absence of auditory input, other sensory modalities may influence cortical structures