Separation anxiety disorder (SAD) involves pathological activation of the attachment system beyond developmental norms. John Bowlby's attachment theory explains how disrupted caregiver-child bonds create internal working models of insecurity that persist into later childhood. Neurobiologically, the amygdala serves as the fear-processing center and becomes hyperactivated in SAD, triggering the hypothalamic-pituitary-adrenal (HPA) axis. This results in excessive cortisol release, maintaining a state of chronic hyperarousal. The prefrontal cortex, responsible for fear extinction and emotional regulation, shows reduced connectivity with the amygdala in anxious children, impairing their ability to modulate fear responses. Developmental neurobiology research demonstrates that the critical period for attachment formation (6-24 months) coincides with rapid amygdala maturation, and adverse experiences during this window can alter neural circuitry governing threat detection and safety signaling. Insecure attachment patterns (anxious-ambivalent) are strongly associated with later development of SAD, as the child internalizes unpredictable caregiver availability as a template for future relationships.