Ancient hallucinogen's brain effects mapped for the first time
Researchers at Northeastern University have mapped how mescaline, one of the oldest known hallucinogen compounds, alters the brain for the first time. In awake rats scanned with fMRI, the cactus-derived psychedelic dampened cerebellar activity while boosting links to sensory and memory regions—suggesting it selectively recalibrates the brain's sensory filter rather than shutting it off.
Key Takeaways
- Mescaline, used ceremonially for roughly 5,700 years, had its brain effects imaged in awake rats for the first time.
- fMRI showed reduced cerebellar activity but stronger links to the hippocampus, thalamus, somatosensory cortex, and midbrain.
- Smell and sound tests point to selective sensory filtering changes, not a total shutdown of cerebellar gatekeeping.
- Researchers say clinical studies are the next step to bridge rodent findings to humans.
The study, published in Neuroscience Bulletin, comes from doctoral student Noah Cavallaro and professor Craig Ferris at Northeastern's Center for Translational Neuroimaging. Mescaline occurs mainly in peyote cacti of the Southwest United States and Mexico and has long been used in spiritual practice.
Like LSD and psilocybin, it can produce visual distortions and altered perception by engaging serotonin-related receptors. Yet Cavallaro argues this ancient hallucinogen may work through different neural pathways—a distinction that could help isolate what actually drives psychedelic experiences. For more breakthroughs at the edge of neuroscience and imaging, explore our Future Tech & AI Wonders hub.
What did the new mescaline brain scans show?
In the first experiment, 24 adult rats—12 female and 12 male—received either mescaline or a control solution. Animals were habituated to the scanner so scans could run without anesthesia. Functional MRI then revealed a paradoxical pattern: activity fell inside parts of the cerebellum, while communication with other regions rose.
The strongest gains linked the cerebellum's deep nuclei to the hippocampus, thalamus, somatosensory cortex, and midbrain. Under normal conditions the hippocampal link was essentially absent; after mescaline it connected to seven of nine hippocampal subregions, Cavallaro told ScienceAlert.
If filtering falters while connectivity to memory, sensory relay, and body-sense areas rises, raw sensory and interoceptive signals may reach regions that usually get only filtered input—offering a plausible mechanism for altered bodily awareness and perception.
Why does mescaline act differently from other psychedelics?
Hyperconnectivity across brain regions also appears with LSD and psilocybin in the lab's rodent work. Mescaline's distinctive dampening of the cerebellum—the sensory "gatekeeper"—sets it apart and may help explain its hallucinatory effects.
Behavioral tests reinforced the selective-filter idea. Rats given mescaline barely responded to a normally rewarding almond scent. In a separate prepulse-inhibition experiment with 16 rats, animals still filtered repeated loud tones at low and high frequencies but failed at middle frequencies. That pattern argues against simply switching the cerebellum off, Cavallaro said—it looks more like recalibrating gain across sensory channels.
Could this research help explain psychiatric symptoms?
Difficulty gating sensory stimuli also appears in some psychiatric conditions. PTSD can involve sound-triggered symptoms and auditory illusions; people in a first schizophrenic episode show hyperconnectivity patterns similar to those seen in mescaline-exposed rodents, the researchers noted.
Caveats remain. Scientists cannot know whether rats experience subjective hallucinations, and heart rate and breathing were not monitored alongside the scans, so some signals might reflect physiology rather than direct neural change. Whether the same cerebellar shifts occur in humans is still unknown. Cavallaro says dosing studies and clinic work are the logical next steps for a drug that has yet to enter clinical use.