Stereotypy and perseverative responding in caged bears: further data and analyses

Abstract

Stereotypies are common in captive animals; yet, their underlying mechanisms are poorly understood. One hypothesis [Garner, J.P., 1999. The aetiology of stereotypy in caged animals. Ph.D. Thesis. University of Oxford, UK] proposes them to be symptoms of altered behavioural organisation (behavioural disinhibition) mediated by striatal dysfunction, and thus, fundamentally analogous to the repetitive behaviours associated with human pathologies such as schizophrenia and autism, or induced in animals by stimulant drugs and striatal lesions. Consistent with this, we previously showed stereotypy frequency to be positively correlated with inappropriate responding during the extinction phase of learning, a measure of ‘perseveration’ consistent with striatal dysfunction, in caged bears [Vickery, S.S., Mason, G.J., 2003. Behavioral persistence in captive bears: implications for reintroduction. Ursus 14, 35–43]. Here, adding new data, we strengthen this finding and look for further evidence of striatal involvement. Twenty-one bears of two species (Asiatic black bears ( Ursus thibetanus) and Malayan sun bears ( Helarctos malayanus)) were taught a simple food rewarded spatial discrimination task. Home cage stereotypy levels ranged between 1 and 45% of all observations (S.E. = 2.75), and high and low stereotypy bears did not differ in the ease with which they learnt the task. However, when responses were no longer rewarded (i.e. food rewards were withheld), as predicted, the most stereotypic animals took the longest to extinguish responding. Contrary to some previous studies, however, further evidence of striatal involvement was limited: behavioural switching rates were not related to stereotypy frequency or to perseveration, and levels of normal activity were only weakly related to perseveration (a trend), leaving the mechanism underlying the relationship between stereotypy and perseveration in these animals unclear. Alternative non-striatal explanations include natural individual variation in habit-formation, general behavioural persistence or compulsiveness and these possibilities require further investigation.