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Question 1

How is the electrode array of a cochlear implant threaded into the cochlear?

Answer 1

Through the round window

Question 2

Describe the loudness decibel ranges for the following:

a) Normal hearing
b) Mild hearing loss
c) Moderate hearing loss
d) Severe hearing loss
e) Profound hearing loss

Answer 2

a) 0-20 dB
b) 20-40 dB
c) 40-60 dB
d) 60-90 dB
e) >90 db

Question 3

What are the target neurons for a cochlear implant?

Answer 3

Spiral ganglion cells

Question 4

Which of the 3 stimulation modes has the lowest power consumption and is the most common? Monopolar, Bipolar, Common ground

Answer 4

Monopolar.

however, bipolar is most effective physiologically (slightly better efficacy/resolution of sound).

Question 5

How does the monopolar stimulation mode work

Answer 5

current passed between one intracochlear electrode and one (or more) extracochlear electrodes (either on telemetry device or as a ball electrode).

Question 6

How does the bipolar stimulation mode work

Answer 6

current passed between a pair of electrodes, both within the cochlea (intracochlear). Nomenclature is BP+X where X defines the number of electrodes between the two electrodes.

Question 7

How does the common ground stimulation mode work

Answer 7

current passed between an intracochelar electrode and all the other intracochlear electrodes connected together.

Question 8

When sound comes in, the outer ear enhaces the sound levels and moves the tympanic membrane (eardrum) back and forth => the malleus (hammer), stapes (stirrup), and incus (anvil) amplify the movement => fluid pushes through the OVAL WINDOW to bend the hair cells => an action potential is fired in the auditory nerve to the brain. From this, what are the 2 primary forms of deafness?

Answer 8

Conductive: damage to the outer or middle ear, blockage, fluid, poor movement of the ossicles, Atresia (closed orifices) or Stenosis (narrowing spaces).

Sensorineual: damage to hair cells from genetics, infection, medications, trauma, autoimmune, aging (presbycusis).

Question 9

what is the difference between inner and outer hair cells

Answer 9

Inner hair cells initiate afferent action potentials when the basilar membrane moves. Outer hair cells receive
efferent action potentials and “tune” the Tectorial Membrane.

Question 10

What is tinnitus

Answer 10

ringing in the ear. The most common cause is damage or loss of the hair cells in the cochlea of the inner ear. This may happen as people age or from prolonged exposure to loud noise. However, there may be other causes, such as earwax blockage.

Question 11

describe how a cochlear implant delivers sound

Answer 11

Microphones on the sound processor pick up sounds and the processor converts them into digital signals. This signal is transferred through the coil to the implant just under the skin. The implant sends the signals
down the electrode into the cochlea. The auditory nerve fibres pick up the signals.

Question 12

How are auditory nerves recruited (fired) by electrodes?

Answer 12

the elctrodes emit biphasic, constant current pulses between selected electrodes.

It is Biphasic to minimize DC. Typical stimulation rates about 1 kHz.

Question 13

what is a modiolus (cochlea)

Answer 13

Spongy bone inside cochlea. The cochlear nerve and spiral ganglion is situated inside it.

Question 14

Why can’t the stimulation parameters be constant?

Answer 14

Nerves are fired by current in the modiolus since this generates voltages in the tissue in proportion to this. Changing impedances affects the voltage. Want to maintain constant current in the modiolus irrespective of the electrode impedance.

Constant current is maintained via voltage stimulators that maintain constant voltage between the electrodes so that the current in the modiolus adjusts accordingly when the electrode impedance changes.

Question 15

why might the impedance of the cochlear implant’s electrode change?

Answer 15

The impedance near the electrode can change due to scar tissue changes.

Question 16

what is Tonotopy

Answer 16

the spatial arrangement of where sounds of different frequency are processed in the brain. Tones close to each other in terms of frequency are represented in topologically neighbouring regions in the brain.

Question 17

why is pitch imporant for humans to distinguish

Answer 17

Important for vowel recognition (formants). Pitch discrimination ability correlates with speech perception.

Question 18

how is loudness processed in the brain (normally and electrically)

Answer 18

normally - Loudness is determined primarily by how many auditory nerves fire.

electrically - It is approxamately equal to the charge per phase

Question 19

how do cochlear implants transmit loudness

Answer 19

they send in more current (longer phases) through the electrodes and more fibres fire.

Question 20

what are the two types of electrode array, and what are their characteristics

Answer 20

Perimodiolar: pre curved to match the cochlea. Closer to the target neurons. Lower current required, reduced spread of excitation (thin current density/position peak). This placement also improves hearing performance i.e. more medial better hearing.

Lateral wall: Straight, flexible. Simple and atraumatic to insert. Wider spread of excitation (wide current density/position peak).

Question 21

How can cochlear implants be customized to suit people who have complete or partial dysfunction of the VIIIth nerve bilaterally due to: Acoustic tumours, VIIIth nerve avulsion (head trauma), or Total cochlea ossification?

Answer 21

Auditory Brainstem Implants. It stimulates the surface of the cochlear nucleus.

Question 22

What is the purpose of the extracochlear electrode (EC1)

Answer 22

the intracochlear stimulation may cause twitching, this channel is to help prevent that.

Question 23

what does “programming” a cochlear implant mean?

Answer 23

Setting stimulation settings.

Electrodes have settings for threshold and comfort levels. Each electrode’s parameters are typically programmed for each individual patient based on their auditory perceptions in response to electrical stimuli.

Additional details like rate, input dynamic range etc. are also adjustable.

Question 24

What is NRT

Answer 24

Neural response telemetry. stimulates the nerve with one electrode pair and then measures the response of the nerve firing with another electrode pair. This information is used to automatically program the cochlear implant. Useful for patients like babies who can’t give feedback.

Question 25

How is NRT used to program a cochlear implant?

Answer 25

Plots increasing stimulation currents on a time vs neuron response graph to find the minimum stimulus at which the patient can hear the sound. It can be performed automatically, with no responses required from the recipient.

Question 26

what is hybrid hearing

Answer 26

Amplifies low frequency hearing (hearing aid/acoustic component) and uses cochlear implants for high frequency hearing. The combined acoustic and electric stimulation travels via acoustic nerve to the brain.

Question 27

Where is the cochlear implant located in hybrid hearing systems?

Answer 27

Electrode inserted into basal part of cochlea for high frequencies

Question 28

What are Totally implantable devices

Answer 28

No external components. This means no components are exposed to continuous wear and tear.

Question 29

What technologies need to be established before totally implantable devices can exist?

Answer 29

Implantable rechargeable battery, High performance implantable microphone that will last a lifetime,
Extremely low power integrated circuit incorporating: Audio and speech pre/processor, Stimulator module, Power management, High voltage output switches.

Question 30

What are the advantages of a totally implantable device

Answer 30

No surgical or post-operative complications. Can be used in invisible mode or with external speech
processor.

Question 31

What are the disadvantages of a totally implantable device

Answer 31

Speech intelligibility is limited in invisible mode (when compared to speech processor). Body noise interference.

Question 32

What is the bottleneck in the electronic auditory pathway?

Answer 32

The Electrode-Nerve Interface in the cochlea

Question 33

what are the two ways the bottleneck in the electronic auditory pathway may be reduced?

Answer 33

Neurotrophins may be used to promote nerve growth toward the electrode. These and other chemical agents can be bound in intelligent polymers and released at controlled rates. Current in vitro experiments result in chaotic growth.

DNA/gene therapy can be combined with a cochlear implant. DNA is released to cause nerves to grow towards electrodes.

Question 34

How can conducting polymers be used to produce better neural stimulation

Answer 34

conducting polymers are more flexible and body-like while being more stable than silicone-based electronics. Polymers such as PEDOT can be grown to intertwine with neural cells, thus lessening the gap between electrode and neuron.

Question 35

What are the expected benefits from using optical stimulating cochlear implant?

Answer 35

optical stimulation is more precise and rate improving than electrical stimulation, which has a spread.

Question 36

what are the drawbacks of using optical stimulations in cochlear implants

Answer 36

they consume more power and release heat.

Question 37

Why might you want to use Laser Ablation on platinum electrodes

Answer 37

Laser surface modification on electrodes minimised Pt dissolution during electrical stimulation and enhanced charge storage capacity of electrodes i.e. it can deliver more charge.