What really happens in the brain during a hallucination?

What really happens in the brain during a hallucination?

Maria Cohut

Recently, a team of researchers from the University of Oregon in Eugene has strived to uncover more information about how hallucinations affect brain activity.

Their new study — conducted in mouse models — has revealed some surprises, which the investigators present in a paper that appears in the journal Cell Reports.

The team found that contrary to what they had expected, the mice experienced reduced signaling between neurons in the visual cortex — the brain region largely responsible for interpreting visual information. The timing of the neurons' firing patterns also changed.

"You might expect visual hallucinations would result from neurons in the brain firing like crazy, or by mismatched signals," notes senior author Cris Niell, who is an associate professor at the University of Oregon.

"We were surprised to find that a hallucinogenic drug instead led to a reduction of activity in the visual cortex," Niell adds. However, he continues, "[i]n the context of visual processing, [...] it made sense."

The researchers also saw that the visual signals sent to the visual cortex were similar to signals sent in the absence of the drug, meaning that the brain still received the same visual information — yet was unable to process it correctly.