What are the causes of hallucinations? The brain may be misinterpreting the lack of information

Mental illness affects millions of Americans. Many people with bipolar disorder, depression, and schizophrenia suffer from hallucinations, the perception of something that is not present. From ghostly odors to voiced harmony and the perception of things that are not there, hallucinations can take many forms and arise from many causes. It's not just a mental illness. Strokes, migraines and diseases of the inner ear can also result in hallucinations. And of course, psychedelic drugs do the same.

Surprisingly, little is known about what happens in the brain during hallucinations. Now, researchers have discovered in experiments on mice that hallucinations reduce the activity of the brain's vision center. The discovery suggests that hallucinations occur when the brain overcompensates for the lack of information from the outside world.

"To understand what is happening in the world, one must reconcile information and interpretation of that information," said in a press release Cristopher Niell, neuroscientist at the University of Oregon in Eugene. "If you give less weight to what is happening around you but interpret it excessively, it could lead to hallucinations."

See and collect

Niell wanted to discover how a hallucinogen called DOI (4-iodo-2,5-dimethoxyphenylisopropylamine) affects the ability of mice to see and perceive the world around them. His hope is to better understand "how we create representations of the world using a vision," he said.

And like LSD and psilocybin, DOI activates a brain receptor for serotonin, a brain chemical that transmits messages between brain cells. Serotonin is better known as a molecule that increases feelings of well-being and happiness, but it also plays a role in vision. Previous research from other groups has implicated the serotonin receptor in hallucinations due to schizophrenia and drugs. Drugs that block the receptor even prevent hallucinations in people with schizophrenia.

Drug Damper

The researchers gave the hallucinogen to mice. Then, as the mice watched images on a screen, scientists scanned the brains of rodents. The researchers observed how the hallucinogen and images affected the brain activity of the mouse. They then discovered that the hallucinogen was attenuating the incoming visual information, scientists reported Tuesday in the newspaper. Cell reports. The discovery suggests that hallucinations stem from a misinterpretation of visual information diminished from the world around us.

"You could expect visual hallucinations resulting from neurons in the brain that go off like crazy or poorly matched signals," Niell said. "We were surprised to find that a hallucinogenic drug instead resulted in a reduction in the activity of the visual cortex."

The discovery suggests that hallucinations come from the brain, filling what he perceives as missing information. But, says Niell, it's probably not the whole story. "I do not think we've necessarily found the smoking gun for all of the underlying causes of hallucinations, but it's likely to be a part of it," he said.