Alzheimer's disease affects millions of Americans, eroding memory and other cognitive functions and driving growing care needs as people age. This project adds deep biological, psychological, and social data collection to an ongoing double-blind, randomized clinical trial comparing psilocybin and dextromethorphan in older adults with low well-being. Participants are healthy adults screened and enriched for biomarkers of preclinical Alzheimer's disease. By layering plasma biomarkers, brain imaging, and neurophysiological measures onto the trial, the study aims to understand short- and long-term changes in brain activity. Deidentified data and biological samples will be curated in the ARPA-H EVIDENT Data and Biorepositories to accelerate future discoveries.