Abstract
Background: Circadian rhythms regulate physiological processes in alignment with environmental light cycles. However, humans—particularly as highly social organisms—demonstrate behavioral and physiological adaptations that follow socially derived cues. This paper introduces the concept of sociodian rhythm, a social counterpart to circadian regulation, and proposes that social entrainment, particularly via eye contact, may serve as a dominant synchronizing mechanism.
Objective: To examine the theoretical basis, biological substrates, and evolutionary implications of sociodian rhythm, with a focus on how eye contact and social cues regulate behavioral and physiological synchrony in humans.
Methods: This review integrates findings from neuroscience, behavioral studies, chronobiology, and ethology to evaluate the interplay between social cues, circadian mechanisms, and eye-mediated neuroregulation. Comparative animal studies, neuroendocrine pathways, and psychophysiological models are also explored.
Results: Social cues—including gaze, pupillary mimicry, and oxytocin release—modulate internal timing systems via pathways involving the suprachiasmatic nucleus (SCN), lateral habenula (LHb), and nucleus accumbens. Eye contact acts as a rapid entrainment mechanism, facilitating alignment in arousal, emotional state, and partnership readiness. Sociodian rhythms may override or restructure circadian rhythms under socially dense conditions.
Conclusion: Sociodian rhythm emerges as a fundamental mechanism for collective behavior and group cohesion. Its regulation through eye contact and oxytocin-mediated synchrony suggests a neurobiological foundation for social timing that complements, and in some cases surpasses, light-based circadian entrainment.