Group Differences in the relationships between Pain Behavior and Brain Morphologic Measures. HIV-by-Pain interaction is observed in the L supramarginal area, R anterior cingulate cortex (ACC) thickness, R lateral OFC thickness, R pallidum volume, L accumbens volume and, bilateral putamen volumes. Graphs showed that HIV individuals with higher pain behavior score tend to have: (1) bigger cortical area in the L supramarginal region and L medial OFC; (2) thinner cortex in the R lateral OFC; and (3) larger subcortical volumes in the R pallidum, L accumbens and, bilateral putamen, but SN controls showed the opposite relationship in these brain measures.