Human immunodeficiency virus (HIV) is a virus that infects vital cells in the human immune system, such as helper T cells, macrophages and dendritic cells. Untreated, the virus causes acquired immunodeficiency syndrome (AIDS), a condition in which the immune system begins to fail, often with fatal results.

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Researchers have found that HIV-related cognitive impairments are similar in some respects to Alzeimer’s-related dementia, particularly the presence of low levels of the protein amyloid-beta in the spinal fluid (this protein tends to accumulate in the brains of patients with Alzheimer’s, leading to lower levels in the spinal fluid), although the progression towards cognitive dysfunction in HIV patients differs from that in patients with Alzheimer’s Disease.

Many HIV patients suffer from cognitive dysfunction and memory problems. Dementia associated with HIV-positive individuals is known as the AIDS Dementia Complex (ADC). It is believed that ADC occurs as a result of brain cells that are infected with the virus, leading to the nervous system and mental symptoms, such as loss of concentration, forgetfulness, loss of memory, problems with thinking, inability to focus for long periods of time and irritability, among others.

Although not its major consequence, HIV also often targets neural systems used by procedural memory, notably in the striatum and basal ganglia parts of the brain. White matter irregularity and subcortical atrophy in these areas, which are necessary for both procedural memory and motor-skills, have been documented in HIV-positive patients. Studies have shown that HIV-positive individuals perform worse than HIV-negative participants in procedural memory tasks (such as the rotary pursuit, mirror star tracing and weather prediction tasks), suggesting that poorer overall performance on such tasks is due to the specific changes in the brain caused by the disease.