Magic mushrooms make lasting changes to the brain (and that’s a good thing).

Technology Networks reports on new Yale University research that apparently explains why psilocybin, the active ingredient in psychedelic mushrooms, has a long-lasting antidepressant effect. The chemical seems to be creating new connections between neurons:

Senior author Alex Kwan, associate professor of psychiatry and neuroscience, said in a press release, “We not only saw a 10% increase in the number of neuronal connections, but also they were on average about 10% larger, so the connections were stronger as well.”

Kwan and his team sought to investigate whether alterations to dendrites, microscopic brain connections that help integrate signals sent from other nerve cells, might be involved. Dendrites are highly plastic, growing and shrinking in response to neurobiological changes. In depression, human studies show that dendritic number and size in the prefrontal cortex reduces. Kwan’s team wanted to see whether psilocybin administration to mice would influence their dendritic density.

To find the answer, Kwan’s team used a powerful imaging technique called two-photon microscopy to look at the density of synapses in the mouse prefrontal cortex. The researchers were able to longitudinally image the brain using this technique, meaning they could examine how dendritic structure changed within the first 24 hours after psilocybin administration, and then repeatedly in the first week after dosing. This was key to determining the strength and endurance of the dendritic connections formed. The researchers showed that roughly 50% of the connections that formed immediately after dosing remained intact a week later. A final analysis 34 days later showed that roughly a third of connections were still intact.

These findings are key to teasing out one of the central mysteries of psilocybin research – why a compound that produces very short-term behavioral changes should produce an antidepressant effect that last far longer.

You can read the study here, in Neuron.