Peek Inside the Brain During Hallucinations, See What Researcher Saw

“Our results do not yet provide a complete explanation of hallucinations,” Niell said. “This is an early explanation of what is going on with individual neurons in one particular brain region.”

Hallucinations are thought to result from a mismatch between what people actually see and how their brains interpret it.

The idea for the study was to perturb visual processing in mice, which have both visual and serotonin systems similar to humans. Although mice can’t describe what they see, Niell’s team was able to focus on physical changes tied to neuron firing before and after drug exposure.

The mice were given 2.5-dimethoxy-4-iodoamphetamine, a chemical variant of mescaline with hallucinogenic effects similar to LSD and psilocybin that is commonly used in animal studies. Such drugs target serotonin-2A receptors and trigger changes in neural responses.

To capture neuronal responses in the live mice, co-author Philip Parker, a postdoctoral researcher, used a high-tech imaging technique to broadly observe changes in brainwide activity, while co-author Angie Michaiel, a doctoral student, used a different kind of imaging to zoom in on the electrical activity of individual neurons in the visual cortex.

Instead of the drug igniting an explosion of activity, researchers saw a 30 percent reduction in neurons lighting up in the visual pathway of the mice in response to a visual pattern presented to them on a computer monitor, compared to before the drug was delivered. Interestingly, the team reported, the mice that had previously learned to recognize the patterns showed an even larger decrease.