Behavioral and physiological antecedents of inhibited and uninhibited behavior

4-month-old infants were specifically selected for patterns of affective and motoric reactivity that were hypothesized to be associated with later inhibited and uninhibited behavior. Infants were classified as high on motor activity and negative affect, high on motor activity and positive affect, or low on motor activity and affect. Brain electrical activity was assessed in these infants at 9 months of age, and behavior toward novelty was observed at 14 months of age. Infants who were high on motor activity and negative affect exhibited greater right frontal EEG activation at 9 months of age and inhibited behavior at 14 months of age. Infants classified as high motor/high positive at 4 months of age exhibited uninhibited behavior at 14 months of age. No relations were found between frontal asymmetry at 9 months of age and inhibited behavior at 14 months of age. However, greater activation in both the left and right frontal hemispheres was associated with higher inhibition scores at 14 months of age. These findings are discussed in terms of the role that affective and physiological reactivity may play in the development of social behavior during toddlerhood.