Excessive Crying, Behavior Problems, and Amygdala Volume: A Study From Infancy to Adolescence.

OBJECTIVE Excessive crying in infancy has been associated with increased risk of later behavioral problems. To identify individuals at risk for behavioral problems and to understand the mechanisms underlying excessive crying and irritability in infancy, research into the neurobiology of excessive crying is needed. We examined if excessive crying and irritability in infancy are associated with behavioral problems and amygdala volume among children and adolescents. METHOD This study included 4,751 singleton children from the prospective population-based Generation R Study cohort, born in the Netherlands in 2002-2006. Excessive crying (>3h on at least 1 day/week) and irritability (Mother and Baby Scales questionnaire) were parent-rated at 3 months. Amygdala volume was measured at 10 years using magnetic resonance imaging, and internalizing and externalizing were parent-rated at 1.5, 3, 6, 10 and 14 years and self-rated at 14 years. Covariates included child age, sex, national origin, gestational age, and maternal age, psychopathology score, parity, education, relationship status and family income. RESULTS Children who cried excessively in infancy had higher parent-rated internalizing (effect estimate 0.20 SD-units, 95% confidence interval [CI] 0.14, 0.27) and externalizing (0.17 SD-units, 95% CI 0.10, 0.24) throughout childhood (linear mixed models), and smaller amygdala volume at 10 years (-0.19 SD-units, 95% CI -0.32, -0.06) (linear regression model). The pattern of associations for both behavioral problems and amygdala volume was similar for irritability. CONCLUSION Excessive crying and irritability in infancy may reflect an early vulnerability to behavioral problems and be linked with neurobiological differences in the development of the amygdala.