The purpose of this research study is to determine if an already FDA approved drug called atorvastatin can help adults, age 75 or older, live well for longer by preventing dementia, disability, or heart disease. Participants will be assigned by chance to receive either atorvastatin (study drug) or a matching placebo (a tablet that looks like atorvastatin but does not contain any medicine). Study engagement may last up to five years and involves in clinic and/or remote visits, survey questions, potential blood draws, in addition to memory and physical tests. After the first 1-2 visits performed in clinic or remote, the study team will follow-up via phone on a yearly basis to see how participants are doing. Participants will be compensated for their time and participation in this research study.

This study will examine how marijuana use can affect oral bacteria and brain health in people with HIV and without HIV. Early studies show that marijuana users have more oral bacteria than non-marijuana users. The increase in bacteria is believed to affect brain health. Participation in the study will be one visit. The visit will take approximately 120 minutes.

The purpose of the study is to see if daily use of nicotine patches will slow or reverse memory loss in participants with Mild cognitive impairment, an early stage of mental decline associated with Alzheimer's disease. Nicotine may mimic natural chemicals in the brain that play a crucial role in memory function, and previous studies have shown that nicotine may improve attention, learning, and memory. In this study, participants will receive either nicotine (up to 21mg/day, the standard dosage of a nicotine patch) or placebo for 2 years to see if these improvements in brain function can be observed over a longer period.

The goal of this study is to determine the pattern of cognitive impairment in chronic stroke, both in terms of performance during cognitive testing as well as brain neurocircuit activation.