A new paper in Nature Communications, covered by Ian Sample at the Guardian, claims a single 25mg dose may leave behind anatomical changes in the wiring itself, still visible 30 days on.
Researchers at UC San Francisco and Imperial College London recruited 28 psychedelic-naive adults and gave each of them a token 1mg primer, then a full 25mg session a month later. They scanned every subject with diffusion tensor imaging, a technique that tracks how water moves along nerve bundles and infers their structural integrity. EEG during the 25mg session showed the expected entropy spike within an hour: the brain was processing more diverse signals at once. A month after the trip, DTI revealed reduced water flow along the bundles linking the prefrontal cortex to midbrain regions — a signature the authors interpreted as either fiber pruning or the growth of fresh, unmyelinated axons.
Senior author Robin Carhart-Harris said it is "remarkable to see potential anatomical brain changes one month after a single dose of any drug," and noted that the volunteers reported improved wellbeing and mental flexibility. The volunteers whose brains went the most chaotic during the dose were also the ones who, weeks later, described the strongest sense of personal insight.
Cornell neuroscientist Alex Kwan, who wasn't involved, said mouse work has already shown psychedelics can rewire connections, and this paper "comes closer than most" to showing the same in humans. He also flagged the obvious caveats: 28 people is a small sample, and DTI is an indirect measure that infers structure from water flow rather than imaging the neurons themselves.
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