The study design is a 30-month (2.5 years) randomized-controlled trial, where eligible participants will be randomized to the CET or EST study treatments. Participants will be treated with the study interventions for 18 months, and then followed for 12 additional months to assess the lasting impact of the study interventions. All participants will complete cognitive, clinical, and neuroimaging (magnetic resonance imaging) assessments prior to starting the study treatments and then at specified intervals thereafter to evaluate the impact of the study treatments on cognition, adaptive function, and the brain.