Читать книгу The Handbook of Solitude - Группа авторов - Страница 56

Rodents’ temperament, particularly behavioral inhibition, has been linked with the extent to which they spend their time socially with others and health‐related outcomes. Cavigelli and her colleagues (2009) assessed rats’ behavioral inhibition based on their latency to approach to novelty in both social and nonsocial situations. In social situations, rats were introduced to a novel rat placed in a wired cage; in nonsocial situations, they were introduced to novel objects. They defined behavioral inhibition as longer than median latency to approach to novelty in social and nonsocial situations. Based on this definition, 30% of any tested group showed behavioral inhibition in both situations. Notably, rats’ responses to social situations and nonsocial situations were unrelated: rats could be slow to approach novel social situations but not slow at approaching novel objects. Latency to approach an object in the nonsocial condition was relatively stable across four months, whereas latency to approach an unfamiliar rat in the social condition was not stable over the same time period. Similar to findings in humans, about 17% of rats demonstrated a stable pattern of behavioral inhibition in social situations assessed four months apart, and these inhibited rats continued to show behavioral inhibition at a third time point (for a review see Cavigelli, 2018).

Importantly, behavioral inhibition predicted shortened life span (Cavigelli, 2018). Stable inhibition during social situations, however, was a better predictor of life span than inhibition during nonsocial situations, suggesting that wariness toward unfamiliar peers may be particularly detrimental to health and thus lead to shorter life spans (see Cavigelli, 2018). This may be because social wariness toward unfamiliar peers may increase stress levels, and lead to the “wear and tear” on the body. It is also possible that behaviorally inhibited rats may interact less with other rats and may not effectively use social partners to reduce their stress levels.

There is some evidence suggesting that behavioral inhibition leads to shorter longevity by altering the functioning of the neuroendocrine system. Behaviorally inhibited rats were shown to have 20–30% more basal glucocorticoids than noninhibited rats (Cavigelli et al., 2009), and greater levels of basal glucocorticoids in young adulthood predicted shorter life spans (Cavigelli et al., 2009). Notably, inhibition during social situations was a better predictor of basal glucocorticoid production and glucocorticoid reactivity than inhibition during nonsocial situations, suggesting that wariness in social situations may play an especially important role in altering the basal functioning of the neuroendocrine system. Behavioral inhibition was also associated with poorer cardiovascular system functioning (higher heart rate and blood pressure), which may be another mechanism by which behavioral inhibition may be linked with shorter life span (see Cavigelli, 2018). Finally, behavioral inhibition was associated with poor immune system functioning (an accentuated inflammatory response), which may also explain why this temperament trait may lead to shorter life span (see Cavigelli, 2018).

Although behavioral inhibition in infancy has been linked with greater basal glucocorticoid production and behavioral inhibition in later life, social experiences in adolescence were shown to moderate these associations (Caruso et al., 2014). Specifically, behaviorally inhibited rats that were housed with novel social partners in adolescence showed less exploratory behavior in adulthood compared to those housed with familiar social partners. On the other hand, behaviorally noninhibited rats that were housed with novel social partners in adolescence showed lower increase in basal glucocorticoid production and increased exploration in adulthood compared to rats that were housed with familiar rats. As such, rats that were noninhibited as infants displayed behaviors and physiology linked with behavioral inhibition. These findings suggested that relatively short‐term social experiences in adolescence may lead to changes in the stability of temperament as well as glucocorticoid production.