Several observations in the present work link HIV expression in the brain to memory impairment, including prevention of HIV brain infection and NCI with systemic antiretroviral prophylaxis; the persistence of brain infection along with cognitive disease, reminiscent of observations in HIV-suppressed NCI patients (20, 51); and the real-time correlation between NCI and expression of tat and nef transcripts that encode proteins implicated in HIV neuropathogenesis (52). This evidence concerns the gene TAT and memory impairment.