Altered hippocampal-prefrontal activation in HIV patients during episodic memory encoding

Objective: To investigate the integrity of hippocampal-prefrontal circuitry during episodic encoding in patients with HIV. Methods: Functional MRI was used to observe changes in blood oxygenation level-dependent ( BOLD) signal in 14 HIV-positive participants and 14 age- and education-matched control subjects while performing an episodic encoding task. Subjects also completed neuropsychological measures of attention and memory. Results: Behavioral results revealed no significant differences in neuropsychological performance. The fMRI results revealed that while both groups recruited brain regions known to be important for successful encoding, including bilateral medial temporal lobes and inferior prefrontal gyri, the HIV group demonstrated significantly reduced signal intensity changes in the right posterior hippocampus, right inferior frontal gyrus, and left lingual gyrus. Additionally, the HIV group exhibited more activity within lateral frontal and posterior parietal regions. Conclusions: This study demonstrates altered integrity of hippocampal-prefrontal regions during episodic encoding in HIV-positive patients. These results extend previous studies that have documented the effects of HIV on fronto-striatal circuits, and suggest the virus functionally impacts the hippocampal system as well.