Intrinsic determinants of temperament.

Infant twins have been recruited to participate in a longitudinal assessment of temperament, beginning at three months of age. The twins are brought into a structured laboratory setting and are videotaped as they interact with the mother, with staff personnel, and with each other. The infant's temperament is rated from the videotapes, and additional data are obtained by having the parents fill out the Infant/Toddler Temperament Questionnaire at each visit. A neonatal assessment has also been done for most twins to obtain initial measures of irritability, reactivity and soothability. Monozygotic twins showed high concordance for irritability as neonates, and for ratings of emotional tone at 12 months. Monozygotic twins also tended to show synchronized patterns of change between ages. The questionnaire ratings correlated significantly with the laboratory ratings at six and 12 months, and this convergent linkage between two sources argues for a core temperament profile that manifests itself with some consistency.