Psychedelics may mess up brain activity scans

Psychedelics can disrupt the relationship between brain neuronal activity and cerebral blood flow measured by fMRI. Researchers at Washington University in St. Louis report that, in mice given a psychedelic that acts on serotonin-linked mechanisms, blood flow signals failed to change in the normal way relative to neuronal activity. Adding a second medication that blocks a serotonin receptor removed these psychedelic blood-flow effects. When the team tested psilocybin in mice, they saw similar neurovascular disruptions. Reanalyzing earlier human fMRI data after psilocybin dosing produced comparable effects, suggesting that fMRI blood-flow and oxygenation signals may be an unreliable proxy for brain activity during and after psychedelic exposure. The findings point to the need to better account for neurovascular effects when interpreting fMRI results in studies exploring psychedelic therapeutic potential, including treatments for mood disorders and substance use disorders.