This study is intended to evaluate the involvement of the neuronal cholinergic receptor system in the accelerated cognitive aging profile seen in adults living with chronic HIV-1 infection. It is estimated by the CDC that by the year 2016, nearly 50% of the US' HIV-positive population will be 50 or older. The HIV-1 virus is known to enter the CNS very rapidly after initial infection, and cause a pattern of persistent neural inflammation, which is deleterious to neurons and glia. This damage is believed to be the basis of cognitive impairment associated with long-term chronic HIV infection, known as HIV-Associated Neurocognitive Disorders (HAND). Successful introduction of Anti-Retroviral Treatment (ART) has greatly reduced the likelihood of progressing to the most severe category of HAND (HIV-Associated Dementia), however the mild and moderate forms (Asymptomatic Neurocognitive Impairment and Mild Neurocognitive Disorder, respectively) are still fairly common even in adults declared "virally suppressed", with little to no detectable peripheral viral DNA/RNA. Prior studies have shown that over the lifetime, more than 50% of adults diagnosed with HIV will experience some degree of cognitive impairment as they age. Some of these changes may be due to cholinergic dysfunction. The acetylcholinergic receptor system is necessary for normal cognitive performance, and is active during working memory, executive functioning, attention, and learning tasks. It has been shown that as the human brain ages, cognitive ability begins to decline, and correlates with declining acetylcholinergic activity. The cholinergic theory of cognitive aging postulates that this loss of activity at cholinergic receptors with age is at least partly responsible for poorer cognitive performance in aging. I will use this model to examine the impact of HIV infection on cholinergic system functioning. This study will use a well-established anti-cholinergic drug challenge model to evaluate cognitive performance in domains of cognitive functioning relevant to cholinergic functioning. Under conditions of temporary muscarinic or nicotinic blockade, or a combination of both, I aim to explore the contribution of putative cholinergic receptor dysfunction to the observed symptoms of HAND. I also intend to determine whether age and HIV-status interact to produce an accelerated pattern of cholinergic cognitive aging that would indicate that older adults with HIV are at higher risk for more rapid cognitive aging than HIV-negative individuals. If successful, the outcome of this study would support the future exploration of novel pro-cholinergic medications to treat cognitive symptoms of HAND, which may improve quality of life for adults living with chronic HIV infection, as they survive into old age.