This neuroscience dissertation tested psilocybin in mouse models of stress and fear learning. Psilocybin improved fear extinction and memory recall, helping animals unlearn fearful associations after both acute and chronic stress exposure. The work suggests psilocybin may act as a rapid-acting antidepressant, with effects tied to serotonin signaling and changes in brain regions like the prefrontal cortex, hippocampus, and amygdala.