Emily Chan
People with schizophrenia often hear voices that aren’t really there, but it has long been unclear why exactly that is, as the illness is poorly understood. Up to 80 percent of people with this mental illness have auditory hallucinations.
Now, a team of scientists at New York University’s Institute of Brain and Cognitive Science on the Shanghai campus believe they have discovered why people with schizophrenia and other disorders experience auditory hallucinations.
“If you look into the cognitive neuroscience research on auditory hallucinations, they always talk about the patients losing the self, losing their agency, that they may have a breakdown in the inhibition function that separates the external world and internal world,” said Xing Tian, the lead author of the study and an associate professor of Neural and Cognitive Sciences at NYU Shanghai. “But something has to generate those ‘weird feelings.'”
In a new study, they put electroencephalogram (EEG) monitors on 40 people with schizophrenia—20 participants heard voices, and the other 20 did not.
The researchers found that the brains of those who experienced auditory hallucinations did not produce the “corollary discharge” signal. This signal quiets our inner monologues and helps our bodies hear sounds coming from our own mouths.
When they prepared to utter a syllable out loud under the instruction of the scientists, the hallucinating group not only failed to turn off their inner monologues, but they also seemed to have a hyperactive response to “efference copy,” a brain signal that is in charge of the motor functions associated with vocalizing.
The auditory hallucinations activate the sound-processing part of the brain. At the same time, they impair some of the motor functions involved with speaking.
As a result, people who have auditory hallucinations do not properly process their inner thoughts, which leads them to think their inner thoughts are outside voices or sounds.
The findings align with the long-held theory that individuals with schizophrenia hear voices that aren’t there because their brains have a hard time telling the difference between their own inner thoughts and external voices. To them, it makes it seem like someone they can’t see is speaking to them.
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