INFANT REGULATION OF THE VAGAL BRAKE PREDICTS CHILD-BEHAVIOR PROBLEMS- A PSYCHOBIOLOGICAL MODEL OF SOCIAL-BEHAVIOR

Cardiac vagal tone is a construct that describes the functional relati onship between the brainstem and the heart. Cardiac vagal tone is meas ured by quantifying the amplitude of respiratory sinus arrhythmia, a c omponent of heart rate variability reflecting the functional output of vagal pathways on the heart. Although there is an extensive literatur e evaluating baseline vagal tone and its relation to behavior, the rel ation between individual differences in the ability to regulate cardia c vagal tone and behavior has been theoretically vague. This article i ntroduces a theoretical model to explain the relation between vagal to ne during steady states and vagal reactivity (i.e., the vagal brake) i n response to environmental challenges. Based upon the proposed model, it was hypothesized that infants who had difficulties in regulating t he vagal brake (i.e., decreasing cardiac vagal tone) during social/att ention tasks would have difficulties developing appropriate social int eractions requiring reciprocal engagement and disengagement strategies . Data from 24 infants are presented. The findings support the model a nd demonstrate that infants with difficulties in decreasing vagal tone during a social/attention task at 9 months of age had significantly m ore behavioral problems at 3 years of age. (C) 1996 John Wiley & Sons, Inc.