Longitudinal evaluation of peripheral photoreceptor atrophy in fundus albipunctatus.

Social connections are a fundamental human need, essential for psychological well-being and health. In 2023, the U.S. Surgeon General issued a landmark advisory declaring loneliness and social isolation a public health epidemic, citing widespread consequences for mental and physical health across the lifespan (). This advisory underscores the urgent need to understand the biological mechanisms through which disrupted social relationships contribute to disease vulnerability. Social relationships take many forms – parent-child bonds, friendships, and social hierarchies – but sexual and romantic partnerships are among the most intimate and biologically significant (). The benefits of these relationships are often revealed through the adverse outcomes that follow their disruption. Social isolation and perceived loneliness have been linked to systemic inflammation (), cardiovascular dysfunction (), increased risk of depression (), stress-related pathologies (), shortened lifespan (; ; ), and heightened risk for neurodegenerative diseases, like Alzheimer’s Disease (; ). Despite widespread recognition of the health benefits of social connection, the mechanisms by which the loss of these relationships leads to compromised health remain poorly understood. Human studies are limited by ethical and practical constraints, but laboratory models have provided critical insights into the neural circuits and brain regions – such as the prefrontal cortex, hippocampus, and hypothalamus – that mediate social behavior and the effects of isolation (; ; ).