A new study finds that schizophrenia patients with auditory hallucinations often hear what they expect to hear. In fact, the hallucinations may be an extreme version of a perceptual distortion quite common among healthy people.
Research has long established that people who experience hallucinations and other psychotic symptoms tend to have elevated dopamine, but the exact link between dopamine and hallucinations has remained unclear.
In the new study, researchers at Columbia University Irving Medical Center (CUIMC) and New York State Psychiatric Institute (NYSPI) found that elevated dopamine could be causing some patients to rely more on expectations, which could then result in hallucinations.
The findings help explain why treatments targeting the production of dopamine could help alleviate this condition.
“Our brain uses prior experiences to generate sensory expectations that help fill in the gaps when sounds or images are distorted or unclear,” said Guillermo Horga, M.D., Ph.D., assistant professor of clinical psychiatry at CUIMC and a research psychiatrist at NYSPI.
“In individuals with schizophrenia, this process appears to be altered, leading to extreme perceptual distortions, such as hearing voices that are not there. Furthermore, while such hallucinations are often successfully treated by antipsychotic drugs that block the neurotransmitter dopamine in a brain structure known as the striatum, the reason for this has been a mystery since this neurotransmitter and brain region are not typically associated with sensory processing.”
For the study, the research team designed an experiment that induced an auditory illusion in both healthy participants and participants with schizophrenia. They observed how building up or breaking down sensory expectations can modify the strength of this illusion. They also measured dopamine release before and after administering a drug that triggers the release of dopamine.
The findings show that the schizophrenia patients tended to perceive sounds in a way that was more similar to what they had been cued to expect, even when sensory expectations were less reliable and the illusions weakened in healthy participants.
This tendency to inflexibly hear what was expected became worse after they were given a dopamine-releasing drug, became more pronounced in participants with elevated dopamine release, and more apparent in participants with a smaller dorsal anterior cingulate (a brain region previously shown to track reliability of environmental cues).
“All people have some perceptual distortions, but these results suggest that excess dopamine can exacerbate our distorted perceptions,” said Horga. “Novel therapies should aim to improve the processing of contextual information by targeting the dopamine system or downstream pathways associated with modulation of perceptual processing, which likely include the dorsal anterior cingulate cortex.”
The study is published in the journal Current Biology.