Prairie voles as a model for adaptive reward remodeling following loss of a bonded partner

Loss of a loved one is a painful event that substantially elevates the risk for physical and mental illness and impaired daily function. Socially monogamous prairie voles are laboratory-amenable rodents that form life-long pair bonds and exhibit distress upon partner separation, mirroring phenotypes seen in humans. These attributes make voles an excellent model for studying the biology of loss. In this review, we highlight parallels between humans and prairie voles, focusing on reward system engagement during pair bonding and loss. As yearning is a unique feature that differentiates loss from other negative mental states, we posit a model in which the homeostatic reward mechanisms that help to maintain bonds are disrupted upon loss, resulting in yearning and other negative impacts. Finally, we synthesize studies in humans and voles that delineate the remodeling of reward systems during loss adaptation. The stalling of these processes likely contributes to prolonged grief disorder, a diagnosis recently added to the Diagnostic and Statistical Manual for Psychiatry. Humans and the socially-monogamous rodent prairie voles exhibit similar emotional and biological responses to pair bonding and partner loss. In particular, neural reward systems are engaged to maintain a homeostatic rewarding state during bonding that drives motivation to be with the partner. Loss disrupts these mechanisms, resulting in yearning. Reward system remodeling therefore likely underlies loss adaptation. However, if this adaptation is stalled, prolonged grief disorder can occur. image