Effects of Psilocybin on Electrophysiology and the Dynamic Content of Thought

Inclusion Criteria: * 18 to 75 years old * Have given written informed consent * Have at least a high-school level of education or equivalent (e.g. GED) and be fluent in English * Be healthy and psychologically stable as determined by screening for medical and psychiatric problems via a personal interview, a medical questionnaire, a physical examination, an electrocardiogram (ECG), and routine medical blood and urinalysis laboratory tests * Agree to consume approximately the same amount of caffeine-containing beverage (e.g. coffee, tea) that he/she consumes on a usual morning, before arriving at the research unit on the morning of the drug session day. If the participant does not routinely consume caffeinated beverages, he/she must agree not to do so on the session day. * Agree to refrain from using any psychoactive drugs, including alcoholic beverages and nicotine, within 24 hours of each drug administration. The exception is caffeine. * Agree not to take any "as-needed" medications on the mornings of drug sessions * Agree not to take sildenafil (Viagra®), tadalafil, or similar medications within 72 hours of each drug administration. * Agree that for one week before each drug session, he/she will refrain from taking any nonprescription medication, nutritional supplement, or herbal supplement except when approved by the study investigators. Exceptions will be evaluated by the study investigators and will include acetaminophen, non-steroidal anti-inflammatory drugs, and commo…