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Schizophrenia is a complex mental illness that affects about one percent of the population; it interferes with a person’s ability to think clearly, manage emotions, make decisions and relate to others. People with schizophrenia may seem that they have lost touch with reality. In fact, one common symptom of the disorder is “hearing voices” in one’s head.
The Voices in My Head
When it comes to schizophrenia, one of the most common questions is where do these inner voices come from? It turns out that people with schizophrenia are actually hearing their own voices in their heads. This is due to a phenomenon called subvocal speech, which most of us experience in a slightly different way.
Have you ever thought so intently about something that you subconsciously said it out loud? Most likely the answer is yes, even if you don’t realize it. For example, you might mutter “take out the garbage” after a partner reminds you for the 100th time. This phenomenon is subvocal speech and, for most of us, it’s a common part of everyday life.
Our brains process all language, even the private thoughts we have in our own heads. These thoughts then transform into “subvocal speech” when this cognitive function stimulates our speech muscles, even though that stimulation is usually not strong enough to generate a voice that anyone could actually hear. You might just mumble under your breath, or make no sound at all.
Subvocal Speech And Schizophrenia
In the ‘50s, a psychiatrist named Louis Gould decided to investigate whether auditory hallucinations in schizophrenia are related to this phenomenon of subvocal speech. Using a technique called electromyography, or EMG, which measures muscle activation over time, he recorded the vocal muscle activity of a group of schizophrenic patients and a group of healthy patients.
When he compared the EMG recordings of schizophrenic patients while they were experiencing auditory hallucinations to those of non-hallucinating patients, he noticed greater vocal muscle activation at times when the patients were hearing voices. This would suggest that while the patients heard voices in their heads, they were simultaneously engaging in subvocal speech. Gould found that by pressing a microphone against the throat of one patient, he could actually hear the subvocal speech that the patient perceived as an external voice.
Inner vs. Outer Voices
But why do schizophrenics believe subvocal speech is an external voice and most people recognize it as their own voice?
Whenever a person hears their own voice, it sets off a “recognition circuit” in the brain. This circuit works by comparing the sound you hear with the expected sound of your own voice; if they match, your brain concludes that the voice was your own. If the heard voice doesn’t match your brain’s prediction, you conclude that someone else is speaking.
Scientists believe that patients with schizophrenia have a defect in this circuit, so their brain incorrectly identifies a mismatch between their own voice and the voice they hear, making them think the voice belongs to someone else. But when they don’t see anyone else speaking, they assume the voices come from inside their heads.
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