Psilocin, the active compound of psilocybin, increased brain-wide activity in rats within 10 minutes of a 2.0 mg/kg dose, with heightened signals across the frontal, temporal, parietal cortex, hippocampus, and striatum. Functional connectivity strengthened between major hub regions like the cingulate cortex and striatum, alongside widespread increases in EGR1, a plasticity-related brain activity marker. The pattern mirrors human imaging findings where psychedelics temporarily loosen rigid brain networks, helping explain why short-lived dosing can lead to longer-lasting shifts in mood and perception.