Arriving home after a long day, you settle in for a quiet evening alone. But instead of the sound of silence, you hear a constant ringing, even though there’s nothing making any noise. What you’re experiencing is called tinnitus, the perception of a noise like ringing, buzzing, hissing or clicking that occurs without any external source of sound. Tinnitus has been bothering humanity since Ancient Babylon, plaguing everyone from Leonardo da Vinci to Charles Darwin. Today, roughly one in seven people worldwide experiences this auditory sensation. So where does this persistent sound come from? When you normally hear something, sound waves hit various areas of your ear, creating vibrations that displace fluid inside the cochlea. If the vibrations are large enough, they elicit a chemical response that transforms them into bioelectrical signals. These nerve impulses are then relayed through the hearing pathway to the brain.
However, in the vast majority of tinnitus cases, the nerve signals that produce these mysterious sounds don’t travel through your ear at all. Instead, they’re generated internally, by your own central nervous system. Under usual circumstances, these self-produced signals are an essential part of hearing. All mammals demonstrate on-going neural activity throughout their hearing pathways. When there are no sounds present, this activity is at a baseline that establishes your neural code for silence.
