In a cohort of HIV-infected patients who are clinically stable on the commonly use regimen of EFV/emtricitabine (FTC)/truvada (TDF) or Atripla, investigators propose to replace the EFV component with an integrase inhibitor, Raltegravir (RAL), given as the RAL and FTC/TDF to evaluate the EFV-related neural alterations. This is a multidisciplinary study which will be lead by Dr. Nina Lin, in collaboration with the research teams of Dr. Alexander Lin, Director of the Center for Clinical Spectroscopy, and Dr. Emily Stern, Director of the Functional Neuroimaging Laboratory, both members of the Brigham and Women's Department of Radiology at Harvard Medical School, as well as Dr. Jane Epstein, a researcher in Dr. Stern's research group. Dr. Epstein is a staff psychiatrist at Brigham and Women's hospital with extensive experience and expertise in research on abnormalities of affective and motivational processing in the context of neuropsychiatric disorders. Investigators will utilize the established clinical research platform in the Infectious Disease outpatient clinical practice at the Brigham and Women's Hospital, where there is currently have many ongoing HIV-related studies and a large panel of HIV-infected patients motivated to be involved in clinically relevant research. Investigators propose to use advanced neuroimaging to measure biologically changes in the brain associated with long-term EFV use with the following specific aims: