De-arousal properties of stereotyped behaviour: Evidence from pituitary—Adrenal correlates in pigs

Abstract

Behavioural and pituitary-adrenal responses of food-deprived pigs, submitted to an intermittent food delivery schedule repeated over several weeks, were investigated. All animals reliably displayed stereotyped activities, in the form of repeated chain pulling, during the interval between food deliveries. The temporal characteristics of this behaviour and its relation to deprivation level suggest its analogy with adjunctive activities. Chain-pulling behaviour was accompanied by decreased pituitary-adrenal activity, as indicated by changes in plasma corticosteroid concentrations between the beginning and the end of the experimental session. When the opportunity to engage in chain pulling was removed, corticosteroid levels did not fall below the pre-session levels. Comparisons of animals able to engage in stereotypies with animals unable to do so because the chain had been removed showed that presession levels of plasma corticosteroids were higher in the former group than in the latter, while post-session plasma corticosteroids did not differ. In addition, the opportunity to engage in adjunctive activities did not protect the animals from the activating effects of extinction on the pituitary-adrenal axis. These data would suggest that stereotypies enable the animals to decrease excessive arousal rather than provide an extra source of stimulation.