Comparing visual hallucinations from psychedelics and from Lewy body diseases

The question

Do the visual hallucinations caused by serotonergic psychedelics resemble those seen in Lewy body diseases such as Parkinson’s disease and dementia with Lewy bodies, and do they share brain mechanisms?

What they did

This is a narrative review: the authors gathered and discussed existing research rather than running a new study or pooling results statistically. They drew on work from neurology, cognitive neuroscience and systems neuroscience, including both human studies and animal models. The focus was on what the hallucinations look like, what brain imaging shows, and which serotonin receptors are involved.

What they found

The authors report that both groups show a range of visual disturbances, from distorted shapes and sizes to fully formed hallucinations, with overlapping features such as illusory motion and encounters with apparent beings. Brain imaging in both cases points to a similar pattern: overactive association cortex (brain regions that interpret and combine information) alongside underactive sensory cortex (regions that take in raw visual input). Psychedelic hallucinations involve serotonin 2A and 1A receptors, while in Lewy body diseases higher levels of serotonin 2A receptors are linked to more hallucinations, and a drug that blocks them (pimavanserin) reduces hallucinations. Two shared brain signatures are highlighted: weaker responses to visual stimuli and a shift toward visual excitation.

The fine print

This is a narrative review, so the studies included were not chosen by a systematic search and the findings were not pooled or graded. Some of the evidence comes from animal models, which may not translate to people. No new patient data were collected, and similar-looking hallucinations do not prove the underlying causes are the same. This summary is based on the abstract only.

What it means

The authors argue that psychedelic-induced visual experiences may be a useful research model for understanding hallucinations in Lewy body diseases, but this is a hypothesis-generating review rather than evidence about treatment.

Evidence grade: Very low. A narrative (non-systematic) review that mixes human and animal findings, with no pooled data or formal quality assessment.

This summary is based on the study’s published abstract.