FEAR-POTENTIATED STARTLE RESPONSES IN TEMPERAMENTALLY DIFFERENT HUMANINFANTS

Previous research has indicated that 4-month-old human infants who exh ibit high degrees of motor activity and negative affect in response to the presentation of unfamiliar auditory and visual stimuli are likely to display behavioral inhibition as toddlers, while 4-month-old infan ts who display high degrees of motor activity and positive affect in r esponse to the same stimuli are likely to be behaviorally exuberant to ddlers. The present study examined baseline and fear-potentiated start le eyeblink responses during a stranger-approach paradigm at age 9 mon ths in a group of infants, some of whom displayed high motor activity and negative affect and some of whom displayed high motor activity and positive affect at 4 months. The analyses revealed that the high moto r/high negative group of infants exhibited a significantly greater inc rease in fear-potentiated startle amplitude at 9 months compared with the high motor/high positive group. There were no differences among gr oups of infants on baseline startle responses. These findings suggest that the origins of behavioral inhibition in early childhood may be li nked to a low threshold for arousal in forebrain limbic areas. (C) 199 8 John Wiley & Sons, Inc.