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The Pathway to Shy

Simone Shane's picture

The notion of “shyness” is something most of us know quite well. In fact, according to prevalence studies, somewhere around 40-50% of American adults have first-hand experience on what it’s like to be chronically shy (1). Although differing from the Big Five personality trait of introversion, in that shy people are in fact fearful of social interaction while introverts merely prefer solitary environments, chronic shyness is often categorized as a characteristic trait (2). The precursor for this shyness trait is frequently cited as the temperament of behavioral inhibition exhibited by very young children (3). When thinking of shyness as a temperament, an innate aspect of one’s personality, we must ask ourselves what the biological underpinnings at hand are.

Research on the physiological correlates of behavioral inhibition has been thoroughly researched by Jerome Kagan and his team at Harvard University (4). Following two groups of children from infancy to age 51/2, Kagan found that the most inhibited group of children had higher and less variable heart rates, larger papillary diameters during cognitive tasks when under psychological stress, more vocal cord tension during cognitive tasks, and higher salivary cortisol levels—the stress hormone—than the group of most uninhibited children at every age of assessment. These physiological differences suggest that the sympathetic nervous systems (SNS) of the inhibited children are more active than their uninhibited counterparts. Furthering this idea, higher indexes of norepinephrine, the principle neurotransmitter released by the SNS in response to stress, were correlated with inhibited behavior in children ages 4 and 51/2—although not at younger ages. Kagan postulates that this heightened activity of the SNS in inhibited children is due to “a lower threshold in the circuit that links the limbic lobe and the hypothalamus to the sympathetic nervous system and its target organs” (Kagan, 1987). Basically, these children seem to be much more easily excitable to novel situations.

Kagan explains the connection of these physiological behaviors to the limbic system by suggesting that the amygdala and hypothalamus of inhibited children react to the unknown or difficult. The amygdala, which processes emotional stimuli and relays these stimuli to the hypothalamus, and the hypothalamus, which then activates the SNS with help from the hypothalamic pituitary adrenal axis (HPA), may just be very sensitive for these children. The connection of the amygdala to behavioral inhibition is interesting since the amygdala is also suspected to play a role in social phobia, which, in the simplest terms, is the DSM-IV diagnosis for severe, distressing, and impairing shyness (5). Indeed, just as many behaviorally inhibited children are later labeled shy, they are also significantly more likely to develop a social phobia as an older child than children without behavioral inhibition (6).

These results seem to lay a clear pathway for the evolution of shyness. Even the statement that no one is born shy by one shyness researcher, Carducci, doesn’t seem to pose a problem to the neat progression of behavioral inhibition to shyness to social phobia. However, the reason that this researcher believes people cannot be born shy presents a problem: namely, since shyness is characterized by self-consciousness and a pervasive negative sense of the self and since children do not display a sense of self until 18 months of age, shyness is just simply not possible until 18 months of age (3). So, are these behaviorally inhibited children with lower thresholds for the new not actually shy? Do “real” shy children who are inhibited due to negative self appraisal stem from another group of infants? Or are behaviorally inhibited infants more likely to garner a negative view of themselves?

In one of Carducci’s studies, 800 shy individuals were given a survey to explain why they thought they were shy and their answers could all be categorized under family factors, personal difficulties, victimization, or other (8). You mean no one answered that it was because their limbic and sympathetic systems had a low threshold for activation? While this survey is important for discovering possible environmental etiologies, it speaks little to biological processes for the simple reason that we’re not aware of them. However, environmental do play a large role in shyness. Of the 40 percent of inhibited infants who became less inhibited by age 51/2, more mothers were aware of their child’s inhibition and had strove to both introduce novel stimuli to their children and help them cope with their stress than mothers of children who remained inhibited (4). In another study, a strong gene-environment association was found as children with a gene that disrupts serotonin transport, the neurotransmitter often associated with depression and anxiety, who had received low maternal social support were assessed as shy at age 7, while children who also had this gene but received adequate support were no shyer than children without the gene (8). However, while this speaks to why some inhibited or “at-risk” children are spared from a shy future, it does not answer the question of how physiological inhibition makes the leap to self-consciousness and negative self-preoccupation.

Under the Wikipedia entry for shyness, it is suggested that shyness is perceived by the shy individual as a negative quality, especially in the individualistic cultures of the West, and that these individualistic cultures may devalue a shy person as either feeble or cold (9). Could the Wikipedia entry be using the term shy in place of behavioral inhibition? Perhaps inhibited children, at some point after their 18th month, get negative feedback about this trait of inhibition, develop self-consciousness, and thus fulfill Carducci’s qualifications of shyness? While Kagan suggests that children’s awareness of their inhibition may help them overcome it (4), could the children who are unable to conquer their social fear not only remain inhibited, but also acquire a negative self-image? What about those children who don’t overcome their inhibition, but do not gain a negative self view? Even though they may cower and both avoid and fear novel social stimuli just as a shy child would, are they quantifiably different because what they fear is not embarrassment or judgment, but simply their physiological response? Perhaps these children become afraid of judgment simply because we think that they are?

On another note, we may be spending entirely too much energy on these temperamentally inhibited children. Are we neglecting those children who just simply become shy without any innate predisposition? If a positive social environment is enough to save children with the morphed serotonin gene, perhaps genetically non-disposed children can become shy, or even just plain inhibited, by environment. Indeed, rats exposed to predator ferrets exhibited not only more signs of behavioral inhibition and heightened HPA activity, but altered gene expression: nuclei of neurons in the amygdala increased their expression of a specific binding protein (10). While this may not tell us that much in the way of self-consciousness (since we can’t really say whether or not rats possess it), it does suggest that stressful event may alter gene expression and make us inhibited even though we previously were not. However, we have only returned to our previous question of where self-consciousness fits in to the equation.

While the origins of self-consciousness still must be explored to complete our picture of shyness and how it develops, the physiological anxiety associated with shyness seems a bit clearer. Whether innate or acquired, the inhibition component of shyness seems to be able to find its roots in the sympathetic nervous system, in conjuncture with the hypothalamus and amygdala of the limbic system. Additionally, we have also seen how dysfunctions in the regulation of serotonin when coupled with a lack of maternal support can also facilitate shy behavior later in childhood. The next step of the puzzle is to research the neurobiological underpinnings of self-consciousness and negative self thoughts. Yet, if self-consciousness is not developed until at least 18 months of age, as Carducci argues, can we be innately disposed to negative thoughts? Could it in fact be social environment that holds the key to the neurological processes, or are genes just not expressed until we reach a certain age? Is negative self-image and self-consciousness related to inhibition in that it also has ties to the limbic and sympathetic systems? Hopefully future research will yield the answers.







(4) Kagan, J., Reznick, J. S., Snidman, N. (1987). The physiology and psychology of behavioral inhibition in children. Child Development, v 58(6), 1459-1473.




(8) Fox, N. A., Nichols, K. E., Hendersen, H. A., Rubin, K., Schmidt, L., Hamer, D., Ernst, M., Pine, D. S. (2005) Evidence for a gene-environment interaction in predicting behavioral inhibition in middle childhood. Psychological Science v 16(12), 921-926.


(10) Rosenboom, P. H., Nanda, S. A., Vaishali, P. B., Trentani, A., Newman, S. M., Kalin, N. H. (2006). Predator threat induces behavioral inhibition, pituitary-adrenal activation and changes in amygdala CRF-binding protein gene expression. Psychoneuroendocrinology v32(1), 44-55.


Other references not directly cited, but potentially useful





Paul Grobstein's picture

shyness: genes, environments, brains


"more easily excitable to novel situations" -> "social fear" -> "negative self-image" -> "shyness" ?

That's an interesting way to think about "shyness", and perhaps behavioral traits generally? Yes, a genetic "influence" but not a genetic "determinant". Instead something that interacts with subsequent influences and so the outcome can be altered by altering any of the subsequent steps. For another possible example, in this case with the opposite of shyness as an outcome, see The Gregarious Brain.