A Cochlear Implant is a small sophisticated electro-medical hearing device. It helps people with severe to profound hearing loss to hear. This device is generally recommended if the person is unable to hear well with conventional hearing aids.
Though both are hearing devices, a cochlear implant is not as simple as a hearing aid which one can remove when not needed. Cochlear implant surgery requires hospitalisation. Since it involves surgery, people would like to know how do cochlear implants work and the different cochlear implant parts.
What Does A Cochlear Implant Do?
Hair cells of the cochlea are very important for us to hear. In case the hair cells are dead or partially damaged, the person is unable to hear. A cochlear implant enables people whose hair cells of the cochlea are dead or partially damaged to hear again. The cochlear implant does the job of the hair cells.
The doctor recommends a cochlear implant to people suffering from severe to profound Sensorineural Hearing loss. Or people who are unable to hear due to the inability of the tiny hair cells to convert sound waves to electrical pulses.
The cochlear implant electrodes provide direct electrical stimulation or electrical pulses in the cochlea of the inner ear which are picked up by the auditory nerve.
The cochlear implant bye-passes the outer ear and the middle ear to directly reach the cochlea in the inner ear. In other words, the cochlear implant does the job of the hair cells in the cochlea by providing electrical stimuli.
Let us understand the functioning of the hair cells of cochlea. This will help us to understand how do cochlear Implants work.
Function Of The Cochlea
Let us understand the working of the inner ear in brief. The cochlea is a snail-shaped organ in the inner ear. The cochlea of the ear contains thousands of tiny hair cells.
These inner hair cells are responsible for converting sound waves to electrical impulses. In case of damage to the cochlea, the damaged hair cells in the ear cannot convert the sound vibrations to electrical pulses.
The Auditory Nerve
The auditory nerve carries the electrical pulses from the cochlea to the brain. Fully or partially damaged hair cells in the ear reduce the sound signals reaching the brain. This results in hearing loss or reduced hearing ability.
Why Does One Need A Cochlear Implant And Not A Hearing Aid?
This is a basic question asked by most people when advised a cochlear implant. Hearing aids do not help some people suffering from severe or profound hearing loss as the speech is not clear with hearing aids.
Hearing aids can only amplify sound, the amplified sound does not help as the cochlea is not functioning normally. The brain does not get the required signal.
These people may find cochlear implants as the means to hear sounds. Read this article on Cochlear Implants vs Hearing Aids to understand the differences.
How Do Cochlear Implants Work?
Cochlear Implants can be broadly divided into two main parts. The external cochlear implant parts which are normally visible, and the cochlear implant parts which are transplanted under the skin at the time of the cochlear implant surgery.
The external cochlear implant parts consist of a microphone, which picks up the sound signal. The sound signal processed by the speech processor passes on through a cable to a coil. This transmitter coil stays in place on the scalp with the help of a magnet.
The Internal cochlear implant components have a receiving coil with a magnet. This receiving coil picks up the signals generated by the transmitting coil. The internal cochlear implant component divides the incoming signal into different frequency bands.
A cochlear implant electrode is placed in the cochlea of the ear. Each frequency band is sent to a different cochlear implant electrode in the cochlea. All the frequency bands are sent to a cochlear implant electrode array or a set of electrodes depending on the number of channels offered by the manufacturer.
Different cochlear implant electrodes carry a different set of frequencies because of the natural function of the cochlea. The sensory hair cells near the outer end of the cochlea are sensitive to or interpret high frequencies only.
The sensory hair cells present towards the inner end of the cochlea are sensitive to low frequencies. Accordingly, the cochlear implant electrode is placed in the cochlea or implanted according to the frequency they are carrying.
So, how do cochlear implants work? In short, the sound signals picked up by the external microphone are processed by the external speech processor and finally reach the cochlear implant electrodes.
These electrical signals are picked up by the auditory nerve and reach the brain. The brain interprets these electrical signals as speech.
The external and the internal cochlear implant parts work together enabling the person with damaged hair cells to perceive or hear the sound.
Check out this video for a visual description of how cochlear implants work:
Let us read in detail about the cochlear implant parts.
Cochlear Implant Parts
As mentioned above, the cochlear implant parts can be divided into externally visible parts and internal parts.
External Cochlear Implant Parts
- Speech Processor Unit with the microphone
- Transmitter coil.
The speech processor is an external part. It comfortably fits behind the ear in a casing that looks similar to a BTE hearing aid. The speech processor unit contains the microphone and the speech processing circuit. A flexible cable connects the processing unit to the transmitter coil which has a magnet.
How Do The External Cochlear Implant Parts Work?
Speech Processor Housing
The Speech Processor is generally situated in the same housing as the microphone. The housing looks similar to a BTE hearing aid but is slightly bigger.
The primary function of the microphone is to pick up the sound, similar to the microphone in a conventional hearing aid. These sound signals are then passed on to the speech processor circuit in the same housing.
The Speech Processor
The speech processor converts the sound signals picked up by the microphone into electrical stimuli or pulses. The speech processor analyses and processes the sound signals. The processing of the sound signals is as per the hearing capacity of the user. After processing, the signals pass on through the cable to the transmitter coil.
The Transmitter Coil
The connecting cable from the speech processor carries the signals to the transmitter coil. The transmitter coil radiates the signals which are picked up by the receiving coil inserted under the skin. The receiver coil transplanted under the skin also has a magnet. Both the coils stay in place with the help of the magnets that attract each other.
Internal Cochlear Implant Parts
The other parts of the cochlear implant are internal and placed under the skin near the ear. This process requires surgery or implantation by an ENT doctor. People think twice before agreeing to cochlear implant surgery as some of them think it could be dangerous, read about the eligibility criteria and the procedure of cochlear implant surgery.
The main internal cochlear implant parts are:
- Receiver coil
- Cochlear Implant Electrode or Cochlear Implant Electrode Array
How Do The Internal Cochlear Implant Parts Work?
The two internal parts are surgically transplanted under the skin. The two parts are the receiver coil unit with a small electronic circuit and the cochlear implant electrode array.
The Receiver Coil
The transplanted receiver coil is placed under the skin behind the ear. The receiver coil picks up the signals given out by the transmitter coil placed just above it on the surface of the skin. Thus, the sound signals radiated by the externally placed transmitter coil are seamlessly passed onto the internal cochlear implant parts.
The receiving coil assembly also has a small electronic circuit that divides the received sound signals into frequency bands. The frequency bands are then sent to the electrode assigned to that particular frequency band.
As mentioned above, the hair cells in the cochlea react to different frequencies depending on their location in the cochlea.
Cochlear Implant Electrode or Cochlear Implant Electrode Array
The circuit attached to the receiver coil unit passes the electrical stimuli or signals onto the cochlear implant electrode array after grouping them in frequency bands. The cochlear implant electrode is placed in the cochlea.
The electrical signals or impulses delivered by the electrodes are picked up by the auditory nerve, this stimulation results in the perception of sound. Since there are multiple stimulation points, they are also called cochlear implant electrode array.
Precaution Is Better Than Cure
After knowing how do cochlear implants work, people should go forward and check if they fit into the criteria instead of struggling with deafness. With early detection and corrective action, we can stop the progression of hearing loss.
Consult your doctor immediately to prevent further damage. Please note that the cochlear implant does not cure the hearing of the affected person. To some extent, it restores the ability to hear the sensation of sound.