Beyond physical isolation: behavioral correlates and potential neurobiological mechanisms of functional social isolation.

Functional Social Isolation (FSI) describes a proposed form of social disconnection in the digital era, wherein individuals are physically co-present yet psychologically detached during pervasive digital immersion. This review examines how everyday digital immersion may contribute to persistent social disengagement, outlines its behavioral correlates and potential neurobiological pathways, and discusses its implications for public health and behavioral psychology. By synthesizing emerging literature on co-present digital immersion, social buffering, and neuroendocrine regulation, we identify five behavioral correlates relevant to FSI: attentional fragmentation, habitual or problematic online engagement, emotional volatility, avoidance of offline social interaction, and reduced practice of offline social skills. We also consider evidence concerning oxytocin, dopamine, norepinephrine, endocannabinoids, serotonin, and cortisol, alongside models of internet-related behaviors. These systems may represent candidate pathways linking digital immersion, attentional capture, affective regulation, and reduced engagement with available social partners. However, current neurobiological evidence is largely indirect and is not specific to FSI; similar patterns may arise from traditional social isolation, chronic stress, sleep disturbance, anxiety, or depression. We therefore present a hypothetical multi-system framework intended to generate testable predictions rather than establish an FSI-specific neurochemical state. FSI may be modifiable through interventions that reduce digital interruptions during face-to-face interaction and support meaningful synchronous engagement. Future research should validate its measurement, test causal pathways, and evaluate interventions across populations and social contexts.