Anxiety disorders represent the most prevalent type of psychopathology across the lifespan. Fear/avoidance, temperament precursors of anxiety symptoms, can be observed reliably in the first year of life. Thus, develop- ment of fear, a critical component of the Research Domain Criteria (RDoC) negative valence constellation, is important in its own right, and represents an early marker of anxiety symptoms. Fearful temperament has been linked with a distinct neurophysiological signature – relative right frontal activation, detectable via electroen- cephalogram (EEG) recording. Dynamic reciprocal effects between the left and right hemispheres contribute to this asymmetry as well as associated behavioral states of fear/avoidance, and shape risk versus protection with respect to anxiety. Maternal sensitivity not only effects fear development, but also moderates links be- tween fear reactivity and anxiety symptoms. The present study addresses an important gap in research, exam- ining reciprocal effects between changes in left and right frontal activation as a vehicle for transmission of anxi- ety-related risk, along with fearful reactivity, considering maternal sensitivity as a moderator. It is hypothe- sized that (1) dominance of right hemisphere change effects on left activation growth across infancy and coupling of accelerated changes in infant fearfulness and shifts in the associated electrophysio- logical signature will confer the risk for anxiety; (2) early maternal sensitivity will serve to attenuate links between psychophysiological risk and anxiety, accentuating it later. The following specific aims are proposed: Aim 1. Infant fearfulness: Modeling behavioral and EEG changes moderated by maternal sensitivity. We will enroll mothers with infants (n=300) at three sites: Pullman, WA, Blacksburg, VA, and Jupiter, FL, re- quired to provide racial/ethnic diversity in the overall sample recruited from otherwise demographically similar communities, and because of data collection/processing demands associated with the longitudinal design. We will conduct multi-method bimonthly assessments of infant fear from 6 to 18 months, relying on a planned missingness design. Infant EEG will be recorded to measure frontal activation along with observations of ma- ternal sensitivity. Dynamic latent change effects will be modeled for behavioral and EEG indicators, providing a picture of development across infancy and setting the stage for Aim 2. Explaining anxiety onset: Contributions of latent change in fear, electrophysiology, and sensitivity. Contributions of changes in fear and related electro- physiology to the emergence of anxiety will be quantified, considering moderation of maternal sensitivity. Chil- dren will be followed until 24 months of age, obtaining questionnaire and structured interview parent-report, as well as observations of behavioral inhibition/anxious behaviors. Latent change scores for fear and frontal EEG power on the left and the right will b...