CARDIAC VAGAL TONE - STABILITY AND RELATION TO DIFFICULTNESS IN INFANTS AND 3-YEAR-OLDS

Psychophysiological studies of infants have found a relation between b ehavioral reactivity and indices of autonomic state. The relation betw een behavioral reactivity, assessed via maternal report, and autonomic state, assessed via cardiac vagal tone in 9-month-old infants was exa mined. Cardiac vagal tone was quantified by measuring the amplitude of respiratory sinus arrhythmia. High cardiac vagal tone was associated with greater behavioral reactivity, resulting in maternal reports of m ore difficult temperament. Stability of the two measures, cardiac vaga l tone and difficult temperament, from 9 months to 3 years of age was demonstrated. In addition, 9-month cardiac vagal tone, independent of 9-month temperament, was related to 3-year difficultness with higher 9 -month cardiac vagal tone being related to less-difficult 3-year behav ior. (C) 1994 John Wiley and Sons, Inc.