Social bonds between family members and friends can last a lifetime. As long as these attachments exist, the selective motivation that drives us to seek out and interact with these individuals represents a healthy, reinforcing mechanism that maintains these bonds. But what happens to these motivational systems when a bond is permanently lost? Most people eventually learn to adapt to the loss of a loved one, but for some, the failure to adapt leads to function-impairing grief that can last years. Clinically, this is known as complicated grief. Despite the central importance of socio-motivational processes and their appropriate transformation following loss, their neuronal basis remains unclear. To address this deficit, I propose to use monogamous prairie voles, which form life-long bonds and exhibit distress following separation from their partner. Pair-bonded prairie voles will lever- press to be reunited with their partner, enabling us to quantify bond-directed motivation. My lab is developing a high-throughput operant system to quantify bond-directed motivation. I will combine this novel behavioral paradigm with advanced neurogenetic tools to interrogate the neuronal substrates of bond-directed motivation. I will test whether bond strength predicts levels of partner-directed motivation and how quickly this motivation extinguishes following permanent partner separation. Then, using our operant paradigm in combination with in vivo Ca2+ imaging and cell-specific manipulations of neuronal activity, I will test the hypothesis that distinct neuronal populations within reward-related brain regions modulate partner-directed motivation. Finally, because some people experience pathological forms of grief characterized by persistent dwelling on the lost bond, I will ask whether artificially reactivating the neuronal ensemble that encodes a pair bond leads to prolonged motivational responses following bond loss. Completion of these experiments will provide fundamental insights into the engagement of social motivation systems at a neuronal level ? both when a bond remains intact and following its disruption. There is a pressing need for this research; there are no currently accepted paradigms for studying selective social motivation or the emotional response to loss. As the U.S. population ages, there will be a substantial public-health burden from increased rates of bereavement-induced mental illness, heart disease, and complicated grief, and this work represents a means to elucidate important biological mechanisms that contribute to these phenomena.
The formation and loss of social bonds dramatically influence human health, but the fundamental biological processes that cement these bonds over time and how these processes are engaged following the loss of a loved one remain unknown. In this investigation, I will use monogamous prairie voles to identify the brain cells that control the desire to be with a mating partner and manipulate these cells to gain insight into the adaptive processes that enable recovery from the loss of that partner. These studies will reveal the biological basis of the emotions that help maintain close relationships and how we recover from the pain of losing them.
