The role of the ventral striatum in inflammatory-induced approach toward support figures

Abstract

Although considerable research has shown that inflammation leads to social withdrawal more generally, it is also possible that inflammation leads to social approach when it comes to close others. Whereas it may be adaptive to withdraw from strangers when sick, it may be beneficial to seek out close others for assistance, protection, or care when sick. However, this possibility has never been explored in humans nor have the neural substrates of these behavioral changes. Based on the role of the ventral striatum (VS) in responding to: (1) the anticipation of and motivation to approach rewarding outcomes and (2) viewing social support figures, the VS may also be involved in sickness-induced approach toward support figures. Thus, the goal of the present study was to examine whether inflammation leads to a greater desire to approach support figures and greater VS activity to viewing support figures. To examine this, 63 participants received either placebo or low-dose endotoxin, which safely triggers an inflammatory response. Participants reported how much they desired to be around a self-identified support figure, and viewed pictures of that support figure while undergoing an fMRI scan to assess reward-related neural activity. In line with hypotheses, endotoxin (vs. placebo) led participants to report a greater desire to be around their support figure. In addition, endotoxin (vs. placebo) led to greater VS activity to images of support figures (vs. strangers), and greater increases in inflammation (IL-6 levels) were associated with greater increases in VS activity. Together, these results reveal a possible neural mechanism important for sickness-induced social approach and highlight the need for a more nuanced view of changes in social behavior during sickness.

Keywords: Close relationships; Cytokines; Functional magnetic resonance imaging; Inflammation; Social approach; Social support.

Copyright © 2014 Elsevier Inc. All rights reserved.

Figures

Fig. 1

Self-reported desire to be around the support figure. Endotoxin led participants to report a greater desire to be around the support figure compared to those who were administered placebo.

Fig. 2

Parameter estimates from ventral striatum (VS) region of interest (ROI) during support figures and strangers for endotoxin and placebo participants. Endotoxin (vs. placebo) led to increased VS activity to images of support figures (compared to serial subtraction). Error bars reflect standard errors.

Fig. 3

Relation between inflammatory response to the endotoxin as measured by log-transformed IL-6 increases from baseline to post-scan and ventral striatum (VS) activity when viewing support figures (vs. serial subtraction) in participants exposed to endotoxin. IL-6 responses to endotoxin were positively correlated with parameter estimates from the VS ROI.