Context: The term temperament refers to a biologically based predilection for a distinctive pattern of emotions, cognitions, and behaviors first observed in infancy or early childhood. High-reactive infants are characterized at age 4 months by vigorous motor activity and crying in response to unfamiliar visual, auditory, and olfactory stimuli, whereas low-reactive infants show low motor activity and low vocal distress to the same stimuli. High-reactive infants are biased to become behaviorally inhibited in the second year of life, defined by timidity with unfamiliar people, objects, and situations. In contrast, low-reactive infants are biased to develop into uninhibited children who spontaneously approach novel situations.
Objective: To examine whether differences in the structure of the ventromedial or orbitofrontal cerebral cortex at age 18 years are associated with high or low reactivity at 4 months of age.
Design: Structural magnetic resonance imaging in a cohort of 18-year-olds enrolled in a longitudinal study. Temperament was determined at 4 months of age by direct observation in the laboratory.
Setting: Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital.
Participants: Seventy-six subjects who were high-reactive or low-reactive infants at 4 months of age.
Main outcome measure: Cortical thickness.
Results: Adults with a low-reactive infant temperament, compared with those categorized as high reactive, showed greater thickness in the left orbitofrontal cortex. Subjects categorized as high reactive in infancy, compared with those previously categorized as low reactive, showed greater thickness in the right ventromedial prefrontal cortex.
Conclusions: To our knowledge, this is the first demonstration that temperamental differences measured at 4 months of age have implications for the architecture of human cerebral cortex lasting into adulthood. Understanding the developmental mechanisms that shape these differences may offer new ways to understand mood and anxiety disorders as well as the formation of adult personality.