Development in the Moment: Does Caregiver Sensitivity Drive Prefrontal Cortex Synchrony? - Every day, 4,000 babies are born into low socioeconomic status (SES) families in the U.S, and these children face disproportionate risks to their language and emotional development. Despite these risks, some will flourish. How do primary caregivers (parents and others) protect young children from SES risks outside of their control? Behavioral studies suggest that real-time factors like caregiver sensitivity (moment-to-moment attunement and responsiveness to a child’s needs) may protect children against larger SES risks like low family income. Existing research suggests that caregiver sensitivity may function as a universal behavioral mechanism driving child brain development across domains. However, the neural underpinnings of these potential real-time mechanisms are unknown. Recent two-brain research suggests that prefrontal cortex neural synchrony (coordinated caregiver-child brain activity) may link children’s socially contingent real-time experiences to their development. However, it is unclear whether or how caregiver sensitivity drives moment-to-moment prefrontal cortex synchrony between caregivers and young children, and whether prefrontal cortex synchrony is linked globally to children’s language and emotion regulation skills. To fill these research gaps, I will investigate two novel aims while building skills, knowledge, and methodical training to advance toward an independent research career. In my first Aim, I test whether moment-to-moment fluctuations in caregiver sensitivity drives moment-to-moment caregiver-child prefrontal cortex synchrony within families. In my second Aim, I will evaluate the association between global prefrontal cortex synchrony and children’s language and emotion regulation skills across families. I have already collected nearly all of the necessary data for my analyses (57 of 60 families collected), and my sample is unusually racially and socioeconomically diverse (majority families of color). Through training activities supported by my collaborators, I will gain the necessary skills to continue investigating neural mechanisms of children’s early development in the context of their close relationships and larger socioeconomic disparities.