A person hears a ringing that isn't there. The doctor asks them to describe it — loudness, pitch, persistence. But it's subjective: one might say "like a mosquito," another "like steam from a kettle." We need a way to see tinnitus directly, in the brain itself.
An electroencephalogram (EEG) records the brain's electrical waves from the scalp — quick and painless, like a microphone picking up sound. Scientists took resting-state recordings from people with and without tinnitus from two different labs. Instead of looking for single spikes, they broke the waves down into their components, like a musician dissecting a chord into notes. It turned out that in people with tinnitus, certain oscillations die out more slowly. It's as if a string, after being plucked, keeps ringing longer than usual.
The most reliable sign is not the frequency of the oscillations but the rate at which they decay. Frequency varies from patient to patient, but slow decay repeats across individuals. It's like how all cars with faulty shock absorbers keep bouncing longer, even if they travel at different speeds.
Such a sign could be used in the clinic: record an EEG, calculate the decay, and tell whether tinnitus is present. It's still an early result, but it shows: the brain gives away its own secret: we just need to read it correctly.
The word "tinnitus" comes from the Latin tinnire, meaning "to ring." The Romans used the same root when describing the clinking of coins.
In the film Primer, the protagonist hears a constant ringing in his ears after a homemade time-travel experiment — perhaps his brain, too, started to decay more slowly.