fMRI Demonstrates How HIV Patients' Brains Compensate for Neurocognitive Damage
Radiologists are using functional MR imaging (fMRI) to define—and possibly predict—patterns of cognitive impairment caused by HIV infection.
By Evonne Acevedo Johnson
"Our preliminary findings have provided evidence that functional MR imaging can be used as a noninvasive biomarker to determine cognitive impairment in HIV patients," said presenter Nina Ventura, M.D., of the Instituto Estadual do Cerebro Paulo Neimeyer in Rio de Janeiro, Brazil.
HIV directly invades the brain, causing glial and neuronal dysfunction. Dr. Ventura's team evaluated 19 patients with HIV and 17 seronegative controls matched by sex, gender and education. Of the HIV-positive patients, nine had no evidence of neurocognitive disorder and 10 demonstrated asymptomatic or mild neurocognitive disorder. Patients were evaluated by neuropsychologists on the same day as MR imaging for differences in executive functions, memory, attention, speed of information, motor skills and verbal language.
The researchers then used resting-state fMRI to evaluate average connectivity, local clustering, within-module connectivity and between-module connectivity of the left and right posterior cingulate gyrus (PCC) and of the left and right medial prefrontal cortex (mPFC).
Patients who demonstrated asymptomatic or mild neurocognitive disorder, Dr. Ventura said, showed a significantly increased PCC efficiency when compared to controls, whereas the patients with no evidence of neurocognitive disorder showed a pattern more similar to controls. "These findings had an opposite correlation to cognitive performance," she said.
The increased PCC efficiency was related to better functioning, particularly in the domain of attention and working memory, Dr. Ventura explained. "This suggests that increased PCC efficiency is beneficial in those patients, functioning as a compensation method. When the increased efficiency is no longer sufficient to compensate the brain damage, patients evolve with cognitive deficit."
Patients with no evidence of neurocognitive disorder, meanwhile, demonstrated a pathological rather than beneficial response—increased PCC local efficiency but decreased cognitive performance.
When brain damage reaches an unknown threshold, hyperconnectivity is no longer sufficient to preserve functioning, "and only at this moment would we observe disconnectivity," Dr. Ventura continued. "This is why the findings are so interesting. We could use fMRI to predict which patients are already using hyperconnectivity to compensate for future irreversible damage."
Neural systems hold "small worlds" of radiologic data, said Dr. Ventura, "with high clustering and short paths that afford specialized processing of information locally while simultaneously permitting large-scale information transfer throughout the network."
"I believe our findings are innovative in the HIV field and corroborate previous studies in other fields, like schizophrenia and traumatic brain injury," said Dr. Ventura, a member of RSNA's Resident and Fellow Committee. "There is a relatively new idea that brain damage could lead first to hyperconnectivity, especially in hub nodes, in order to preserve functioning."