You are in a crowd when you hear your name. You turn, looking for the speaker. No one meets your gaze. It dawns on you that the voice you heard must have sprung from your own mind.
This foray into the uncanny is as close as most people come to experiencing auditory hallucinations or "hearing voices," a condition that affects 70 percent of patients with schizophrenia and 15 percent of patients with mood disorders such as mania or depression. For these individuals, instead of hearing just one's name, voices produce a stream of speech, often vulgar or derogatory ("You are a fat whore," "Go to hell") or a running commentary on one's most private thoughts.
The compelling aura of reality about these experiences often produces distress and disrupts thought and behavior. The sound of the voice is sometimes that of a family member or someone from one's past, or is like that of no known person but has distinct and immediately recognizable features (say, a deep, growling voice). Often certain actual external sounds, such as fans or running water, become transformed into perceived speech.
One patient described the recurrence of voices as akin to being "in a constant state of mental rape." In the worst cases, voices command the listener to undertake destructive acts such as suicide or assault. But hearing voices is not necessarily a sign of mental illness, so understanding the mechanics of auditory hallucinations is crucial to understanding schizophrenia and related disorders.
For example, your occasional illusionary perception of your name spoken in a crowd occurs because this utterance is uniquely important. Our brains are primed to register such events; so on rare occasions the brain makes a mistake and reconstructs unrelated sounds (such as people talking indistinctly) into a false perception of the spoken name.
Hallucinated voices are also known to occur during states of religious or creative inspiration. Joan of Arc described hearing the voices of saints telling her to free her country from the English. Rainer Maria Rilke heard the voice of a "terrible angel" amid the sound of a crashing sea after living alone in a castle for two months. This experience prompted his writing the Duino Elegies.
How can we understand differences between an inspired voice, an isolated instance of hearing one's own name, and the voices of the mentally ill? One answer is that "non-pathological" voices occur rarely or perhaps only once. Not so for the person with mental illness. Without treatment, these experiences recur relentlessly.
Brain imaging studies have found that parts of the temporal lobe activate during these hallucinations. Our research at Yale University, as well as studies conducted at the Institute of Psychiatry in London, also detected activation in an area of the brain known as Broca's region during production of "inner speech" or verbal thought.
One theory is that voices arise because Broca's area "dumps" language outputs into parts of the brain that ordinarily receive speech inputs from the outside. To test this theory we are using trans-cranial magnetic stimulation (TMS) to reduce the excitability of portions of the temporal lobe and Broca's region.
So far, most patients appear to experience significant improvements from TMS directed to both brain regions, with improvements lasting from two months to over a year. These results, although preliminary, suggest an alternative treatment if validated in larger-scale studies.