The initial behavioral reaction to unfamiliar events is a distinctive source of intraspecific variation in humans and other animals. Two longitudinal studies of 2-year-old children who were extreme in the display of either behavioral restraint or spontaneity in unfamiliar contexts revealed that by 7 years of age a majority of the restrained group were quiet and socially avoidant with unfamiliar children and adults whereas a majority of the more spontaneous children were talkative and interactive. The group differences in peripheral physiological reactions suggest that inherited variation in the threshold of arousal in selected limbic sites may contribute to shyness in childhood and even extreme degrees of social avoidance in adults.

We investigated the hypothesis that beat-to-beat variability in hemodynamic parameters reflects the dynamic interplay between ongoing perturbations to circulatory function and the compensatory response of short-term cardiovascular control systems. Spontaneous fluctuations in heart rate (HR), arterial blood pressure, and respiration were analyzed by spectral analysis in the 0.02- to 1-Hz frequency range. A simple closed-loop model of short-term cardiovascular control was proposed and evaluated in a series of experiments: pharmacological blockades of the parasympathetic, alpha-sympathetic, beta-sympathetic, and renin-angiotensin systems were used to open the principal control loops in order to examine changes in the spectral pattern of the fluctuations. Atrial pacing was used to examine blood pressure variability in the absence of HR variability. We found that respiratory frequency fluctuations in HR are parasympathetically mediated and that blood pressure fluctuations at this frequency result almost entirely from the direct effect of centrally mediated HR fluctuations. The sympathetic nervous system appears to be too sluggish to mediate respiratory frequency variations. Low-frequency (0.02-0.09 Hz) fluctuations in HR are jointly mediated by the parasympathetic and beta-sympathetic systems and appear to compensate for blood pressure fluctuations at this frequency. Low-frequency blood pressure fluctuations are probably due to variability in vasomotor activity which is normally damped by renin-angiotensin system activity. Blockade of the alpha-adrenergic system, however, does not significantly alter low-frequency blood pressure fluctuations.

Longitudinal study of 2 cohorts of children selected in the second or third year of life to be extremely cautious and shy (inhibited) or fearless and outgoing (uninhibited) to unfamiliar events revealed preservation of these 2 behavioral qualities through the sixth year of life. Additionally, more of the inhibited children showed signs of activation in 1 or more of the physiological circuits that usually respond to novelty and challenge, namely, the hypothalamic-pituitary-adrenal axis, the reticular activating system, and the sympathetic arm of the autonomic nervous system. It is suggested that the threshold of responsivity in limbic and hypothalamic structures to unfamiliarity and challenge is tonically lower for inhibited than for uninhibited children.

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This study adds to the growing literature suggesting an association between behavioral inhibition and social anxiety disorder and an inverse relationship between inhibition and disruptive behavior disorders.

Longitudinal study of 2 cohorts of children selected in the second or third year of life to be extremely cautious and shy (inhibited) or fearless and outgoing (uninhibited) to unfamiliar events revealed preservation of these 2 behavioral qualities through the sixth year of life. Additionally, more of the inhibited children showed signs of activation in 1 or more of the physiological circuits that usually respond to novelty and challenge, namely, the hypothalamic-pituitary-adrenal axis, the reticular activating system, and the sympathetic arm of the autonomic nervous system. It is suggested that the threshold of responsivity in limbic and hypothalamic structures to unfamiliarity and challenge is tonically lower for inhibited than for uninhibited children.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. This content downloaded from 134.Inhibition to the Unfamiliar. CHILD DEVELOPMENT, 1984, 55, 2212--2225. A group of 43 children classified as either behaviorally inhibited or uninhibited at 21 months were observed at 4 years of age in situations designed to evaluate behavior with an unfamiliar peer, heart rate and heart rate variability to cognitively challenging tasks, reluctance to answer difficult questions, and differential fixation of an active and passive figure in various scenes. At age 4, the 22 formerly inhibited children, compared with the 21 uninhibited children, were socially inhibited with the other child, displayed a higher and more stable heart rate, were more reluctant to guess at difficult problems, and preferentially fixated the passive figure. Additionally, the mothers' descriptions of their children were in accord with the observed behaviors. These data, which are consonant with the work of others, suggest that a tendency toward behavioral inhibition or lack of inhibition to the unfamiliar is moderately stable over the preschool years and possibly influenced by biological factors.Encounter with a person, object, feeling, or situation that is unfamiliar or unexpected is one of the most pervasive features of human experience. During the first seconds, while the mind works at understanding and, if necessary, coping with the intrusive information, individuals are in a special psychological state one might call uncertainty to the unfamiliar.Perhaps the orienting reflex, described by the Russian physiologist Sokolov (1963), and the third positive wave of the event-related potential (Donchin, 1975), are physiological accompaniments to the very early stages of this state. However, individuals react in different ways in response to the state of uncertainty. Among young children, some become quiet, cease the activity in which they are engaged, retreat to a familiar person, or withdraw from the field in which the unfamiliar event occurred. Other children, of similar intellectual ability and social background, show no obvious change in their ongoing behavior, and may even approach the unfamiliar event. We call the former group inhibited, and the latter, uninhibited (Garcia-Coll, Kagan, & Reznick, 1984). Parents often call the former class of child watchful, shy, or vigilant, and the latter exploratory, outgoing, or fearless.

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