Olfactory Function and Model-Based Behavior in People Living With HIV and SUD

Study Description: Cognitive impairments persist in people living with Human Immunodeficiency Virus (HIV) despite anti-retroviral therapy (ART). However, these impairments remain under-characterized and it is not clear whether they include deficits in model-based control of behavior. HIV is common in people with substance use disorder (SUD) but the combined impact of HIV and SUD on cognition remains unclear. The olfactory system is uniquely vulnerable to neurodegeneration and overlaps with brain regions involved in decision making. This study will investigate olfactory function and model-based behavior in people living with HIV and SUD, and relate these measures to biomarkers of neurodegeneration. Objectives: The primary objective of this protocol is to compare olfactory function and performance on behavioral tasks assessing model-based behavior between people living with and without HIV, and between people with and without SUD. Secondary objectives of this protocol are to compare blood-based and MRI-based biomarkers of neurodegeneration between people living with and without HIV, and between people with and without SUD. Endpoints: Primary: * Olfactory function (Sniffin Sticks Threshold, Discrimination, and Identification tests) * Behavior on tasks assessing model-based behavior (outcome devaluation and sensory preconditioning) Secondary: * Blood-based biomarker of neurodegeneration (Neurofilament Light Chain \[NfL\]) * MRI-based biomarker of neurodegeneration (Magnetic Resonance Imaging)