Brain scans of older HIV-positive individuals show deficits in cognitive functioning as compared to age-matched healthy controls, according to a new study.
The increased prevalence of HIV among adults age 50 and older underscores the importance of improving the understanding of mechanisms causing HIV-associated neurocognitive disorders (HAND), which affects from 30% to 60% of those infected with HIV, according to lead author Xiong Jiang, PhD, a neuroscientist at Georgetown University Medical Center in Washington, DC.
The new study suggests that cognitive impairments in HIV-infected individual age 50 years or older might be even more prevalent than previously thought. This could be because some standard neuropsychology tests might be insensitive to HAND, he said.
"While there is no proven treatment that can effectively treat HAND other than control HIV replication, it is important for caregivers, families, and the individuals themselves to know if they are affected," said Jiang.
Jiang and colleagues used a validated design to examine the behavioral and neural profile of impaired cognitive control in 14 adults, aged 52 to 64; 9 were HIV-positive and 5 were age-matched, healthy controls. During functional MRI, the participants were cued to judge the gender of a face (male or female) or the meaning of a word (for example, animate for "tiger" and inanimate for "table") on superimposed face-word images. A switch in task after the cue often leads to an increase in reaction time and a decrease in accuracy, known as switching cost, Jiang said.
The results show that the HIV-positive group was significantly slower in adjusting to change in tasks, which the researchers said correlates with brain dysfunctions in the dorsal anterior cingulate cortex--a key brain region for executive function.
Jiang said that the anterior cingulate cortex might be one of commonly affected brain regions in HIV and a potential neural target for therapies.
The researchers concluded that their novel findings have a few important implications: “First, the prevalence of cognitive impairments in HIV-positive older adults might be even higher than previously proposed; second, anterior cingulate cortex (in particularly its dorsal region) might be one of the key regions underlying cognitive impairments (in particularly executive functions) in HIV; and third, it might be beneficial to adopt paradigms developed and validated in cognitive neuroscience to study HAND, as these techniques might be more sensitive to some aspects of HIV-associated neurocognitive impairments than standard neuropsychology tests.”
The findings from this small study are preliminary, they admitted. However, they stated that the results “clearly demonstrate the sensitivity and applicability of this technique in detecting reduced executive function in HIV, and uncovering its neural basis.”
The researchers plan to study HAND in a larger population to further develop imaging-based biomarkers with the potential to guide and evaluate early and targeted therapies in HIV-positive patients.