Project Summary Anxiety disorders affect one third of the US population, significantly burdening individuals and society. Although rates peak in late adolescence, anxiety disorders have origins in infant and early childhood temperament. Moreover, beyond predicting risk for later anxiety, early temperament even more strongly predicts later neural correlates of anxiety. As such, temperament may identify an enduring neural “risk signature.” Precisely characterizing this signature may generate knowledge that would help reduce the burden of long-term mental health problems. However, most research quantifies such neural risk signatures in older children and adults. Thus, it remains unclear whether such a risk signature, involving temperament and brain function, manifests in infancy before predicting later behavior. Here, we propose to recruit a sample of typically developing 3-5-month-old infants screened to identify negative reactive temperament, characterize their brain networks using magnetic resonance imaging (MRI), and assess their Behavioral Inhibition (BI) at 13-15 months of age. Our prior work uses novelty-evoked motor activity and behavioral distress to quantify a temperamental bias called negative reactivity. This bias predicts later avoidance of unfamiliar stimuli or contexts during early childhood, a pattern called BI. BI, in turn, is associated with functioning in the brain’s salience and ventral attention networks. Moreover, BI is the best early-child behavioral predictor of later anxiety disorders, conditions also associated with functioning in the salience and ventral attention networks. We will test the hypothesis that behaviorally assessed negative reactivity in early infancy is associated with decreased functional connectivity in the salience and ventral attention networks relative to non-reactive infants. Identifying the neural underpinnings of heightened negative reactivity in infancy and links to BI will elucidate the neurobiological origins of risk for the development of anxiety.