Our ears have three major parts — the outer ear, the middle ear, and the inner ear. The inner ear houses the hearing organ called the cochlea. It is a small snail-shaped structure within the inner ear. Inside the cochlea, there are over 20 thousand hair cells that communicate with the auditory nerve and send electrical signals to the brain. The brain interprets those signals and assigns meaning to them, so that we can understand what we hear.
With hearing loss, those hair cells in the cochlea are damaged and do not send strong enough signals to the brain. The first way we improve this problem is through hearing aids. Hearing aids amplify sound, so the signal is sent to the brain more effectively. This works at first— however, when the hair cells in the cochlea are significantly damaged, amplification begins to distort the sound. Like a bad radio signal, it’s still not clear when you turn up the volume. When hearing aids are no longer helpful, we start thinking about a cochlear implant as an option for improved hearing.
A cochlear implant functions differently than a hearing aid. Instead of amplifying sound, a cochlear implant bypasses the damaged hair cells in the cochlea, which is where the distortion comes from, and directly stimulates the auditory nerve, to improve the signal that is being sent to the brain.
How Do Cochlear Implants Work?
A cochlear implant has two major parts — the internal device and the external device.
The internal device is the surgically implanted part of the cochlear implant (3). It is a receiver for sound, and includes an electrode array, transmitter, computer chip, and magnet. The internal device is responsible for receiving sound from the external device and transmitting it to the auditory nerve (4). The internal device alone does not have any power, so it does not work by itself. It must be connected to the external device in order for you to hear.
The external device is also known as the sound processor (1). It is a battery-operated transmitter for sound. It has a component that sits behind your ear (1), with two microphones that pick-up sound. The sound is then processed by the external device and sent up the cable to the coil, which is attached to your head by a magnet (2). This magnetic connection allows the external device to communicate with the internal device. Newer technology includes all of these components (processor, coil, cable, magnet, battery) into a single unit that is off the ear and connected to the head by the magnet alone.
Surgery is an out-patient procedure that lasts approximately one hour (although it might feel like you’re there all day with the early check-in times and the recovery period). During the procedure, the patient is put under general anesthesia. The surgeon will make an incision along the fold behind the ear. Minimal drilling is done through the skull to reach the inner ear, which is where the electrode array is threaded into the cochlea. An audiologist will also be present during surgery to test the cochlear implant and ensure it is working properly.