Growing evidence for the safety and efficacy of psychedelics could lead to better treatments for anxiety, depression, pain, and other often intractable conditions. Jerry Rosenbaum was intrigued when he first heard about the effect that psilocybinthe hallucinogenic compound found in certain species of mushrooms"was purported to have on the brain's "resting state," what neuroscientists call the default mode network. The default mode network encompasses any neural function that has some bearing on our autobiographical tendencies. When people take psilocybin at low doses, the default mode network becomes less active. That is, the drug appears to tame self-reflection and all but ruin rumination, that obsessive mental state characterized by excessive, repetitive thoughts. Rumination is a hallmark cognitive symptom of depression. Neuroscientists are observing that, when taken in a controlled setting, these substances are beneficial to the brain, especially for people who have certain psychiatric disorders. Landmark studies in 2014 and 2016 showed that LSD and psilocybin alleviated existential anxiety in patients with life-threatening illnesses for up to a year after beginning the treatment. Other studies have shown that ketamine may strengthen neurons against the damage from chronic stress by preventing synapses from being flooded with glutamate, an amino acid that, in excess, withers dendrites. And researchers continue to investigate whether psychedelics are useful as anti-inflammatory agents.