Amygdalae Enlargement and Activation are Associated with Social Network Complexity in Individuals with Human Immunodeficiency Virus (HIV)

Brain volumetric studies reveal that human immunodeficiency virus (HIV) infection is associated with significant changes in several neural regions, including enlargements in the amygdalae, which are small subcortical structures located deep within the left and right temporal lobes that contribute to social behavior. Research on healthy individuals has shown a positive correlation exists between amygdalae volumes and social network size. However, there is evidence that larger amygdalae volumes are associated with increased psychiatric difficulties. The present study investigated the relation of amygdalae volumes and activation to social network size in HIV patients. It was predicted that HIV participants would demonstrate amygdalae enlargement and hyperactivity, and that this would correlate with reduced social interactions. The Social Network Index (SNI), a self-report measure that assesses involvement in eight social domains, was administered to 14 HIV positive (HIV) and 7 healthy control (HC) individuals. The psychological profiles of the groups were characterized using several self-report questionnaires, measuring current stress levels, mood, rates of interpersonal difficulties, and alexithymia. High resolution anatomical magnetic resonances images (MRI), obtained using a 3-Tesla scanner, were used to quantify amygdalae volumes. Participants viewed black and white images of angry and fearful faces, stimuli known to elicit robust amygdalae activation, as part of a functional MRI paradigm. The HIV and HC groups did not significantly differ on measures of social functions, amygdalae volumes, or amygdalae activation. In both groups, trend level correlations were observed between increased left amygdala volume and social network size. We also observed a significant correlation between right amygdala activation and social network complexity in the HIV group; however, these correlations were not significant in the HC group. Taken together, our results indicate that in HIV patients, greater amygdalae volumes and activation in response to highly potent social stimuli were associated with a higher degree of social interaction. These data have high clinical significance in that they provide preliminary evidence that individuals with HIV demonstrate a similar relation between social functions and amygdalae structure/function, as has been previously shown in HC samples. Studies with larger samples are needed in order to investigate these preliminary findings further