Four steps to sound: how a cochlear implant talks to the brain
It is one of the most sophisticated pieces of technology ever designed for the human body - yet it fits behind your ear and weighs less than a coin. A cochlear implant works in four elegant steps, each one handing off to the next in a fraction of a second, every moment you are awake.
Here is what happens every time a cochlear implant user hears a sound.
Step 1: The microphone listens
A small microphone sits behind the ear, in a processor that looks much like a hearing aid. It picks up sound from the environment - a voice, a car horn, music, a bird. Everything the world has to offer acoustically passes first through this tiny device.
Step 2: The processor translates
Inside the processor is a miniature computer that performs a remarkable act of translation. It converts the acoustic sound into digital code - a pattern of electrical pulses that represents the frequency, intensity, and timing of that sound. This happens continuously, in real time, thousands of times per second.
Step 3: The signal crosses the skin
The digital code is transmitted wirelessly - through the skin, with no wires and no discomfort - to a small receiver implanted just beneath the scalp. A magnet holds the external processor in place over the implant. The transmission is instant and invisible.
Step 4: The nerve receives
The internal implant contains an array of electrodes, positioned inside the cochlea. Each electrode corresponds to a different frequency of sound. The device sends precisely timed electrical pulses to the relevant electrodes, which in turn stimulate the hearing nerve. That nerve carries the signal to the brain, which interprets it as sound.
"The cochlear implant is arguably the most successful neural prosthesis ever developed. It restores a sense - hearing - through direct electrical stimulation of a sensory nerve, and it does so with a reliability and quality that continues to improve with every generation of device." - Prof. Fan-Gang Zeng, University of California Irvine - Centre for Hearing Research
The result is hearing. Not perfect hearing - the brain must learn to interpret the new signals, which takes time - but genuine, functional hearing. Conversation. Music. The voice of someone you love.
For someone who has lived in silence, these four steps are a quiet miracle happening hundreds of times every second.
Expert source: Prof. Fan-Gang Zeng, UC Irvine Centre for Hearing Research