Lecture 20 Flashcards
(15 cards)
effects of hearing impairment
- Simplest effect is on detection
- Discrimination is also affected (resolution comprimised)
- Discrimination of audible cues also affected
theoretical basis of cochlea implant
sensorineural hearing loss mostly loss of hair cells
neural elements often still intact (SGC)
in theory we can stimulate the normal firing pattern of the auditory system
where is the tonotopic organisation preserved
brain stem, midbrain nuclei, primary auditory cortex
what was an extra-cochlear implant adn its issues
attempt to have an implant outside the cochlea to avoid damage
Didnt work well and came with unwanted sensation through stimulation of the facial nerve and pain fibres
components of a cochlear implant in order
microphone
Speech (sound) processor
transmitter coil
receiver/stimulator
electrode array
- Microphone
o Transduces acoustic signal into an electrical signal
- Transmitter coil
o Uses radio frequency induction to send data and power to receiver/stimulator
- Speech (sound) processor
External part looks like a hearing aid. It extracts information from the acoustic signal and codes for transmission
- Receiver/stimulator
o Goes under the skin and receives data and power and decodes into signal for electrode stimulation
- Electrode array
wire enters middle ear space via posterior tympanotomy
enters scala tympani via round window
Delivers electrical stimulation to auditory nerves (spiral ganglion cells)
what is a contour electrode
Stylet (wire) keeps electrode straight for insertion and is then withdrawn to allow array to curve
attempts to follow curve of the cochlear spiral to place electrodes closer to spiral ganglion cells
What is the type of electricity used to stimulate the auditory nerve in the cochlea
bi-phasic charge balanced current pulses
Electrochemical reactions occur between metal and fluid as the current goes from one to the other. If current only passed in one direction, a build-up of toxic products, this can destroy the nerve cells. Hence it is important that it is a bidirectional current.
what is a speech processor MAP
shows comfort levels and electrical thresholds for particular electrodes
These unique levels are programmed into the external sound processor
Transcutaneous and percutaneous implant difference
Percutaneous: implant had a direct hard‐
wired connection through the skin to the electrode(s). Simple but higher risk of infection
Transcutaneous: radio frequency induction was used to transmit information and power through the intact skin. More complex but better for long term use
What do modern cochlea implants use?
- multichannel
- intracochlear electrode
- transcutaneous transmission
