Psychophysiological correlates of infant temperament: stability of behavior and autonomic patterning from 5 to 18 months.

The stability of infant temperament and autonomic patterning (heart period and cardiac vagal tone) was examined longitudinally when infants were 5, 10, and 18 months of age. Behavioral measures of reactivity and regulation to frustration tasks, and maternal perceptions of infant temperament were obtained at each age along with baseline measures of cardiac activity. No stability was found from 5 to 10 months while some stability of behavior and autonomic patterning was identified from 10 to 18 months, with the exception of negative reactivity. High levels of cardiac vagal tone (V) were associated with negative reactivity at 18 months. When examining groups based on degrees of reactivity and regulation, we found infants who responded negatively to frustration but who also displayed more regulatory behavior to have higher V.