Psychedelic aftereffects may offer a window into psychotic symptoms

A 25-year-old man once saw a large, unblinking eye in his ceiling after taking psychedelics, but he did not have psychosis nor had he been using drugs. This incident led him to contact Max Greenwald, an M.D.-Ph.D. student at Yale School of Medicine, who wondered if he might be at risk for developing psychosis. The study led by Greenwald and Albert Powers, M.D., Ph.D., explores the lingering visual effects, known as persisting perceptual abnormalities (PPAs), that some people experience after using psychedelics such as psilocybin or LSD.

These effects, which have been recognized for decades as HPPD, are more common than many might think. Over half of the 186 psychedelic users in the study reported experiencing PPAs after using the substances, and most did not experience distress. Interestingly, younger users who started using psychedelics were more likely to report these effects.

The study suggests that using psychedelics while the brain is still developing may increase the likelihood of experiencing these effects. Early signs of psychosis often include subtle changes in perception, such as brighter colors or louder sounds. Greenwald notes that these perceptual abnormalities seen in prodromal psychosis resemble those that persist after psychedelic use.

The researchers also found that people who experienced PPAs saw more phantom stripes, felt more confident about them, and were worse at distinguishing real patterns from static. However, they did not show increased reliance on expectations, which suggests a noisy visual system that is more prone to false positives. This noisy system, according to the researchers, could be influenced by the brain's top-down expectations, which act as templates for interpreting sensory input.

While the study does not definitively prove that psychedelics cause these changes, it highlights the potential link between PPAs and the early stages of psychosis.