startling events, and is accompanied by underlying neurochemical changes such as enhanced dopamine activity (Würbel 2001). Based on significantly fewer instances of abnormal behaviors (i.e., stereotypies) encountered in wild-caught animals vs. their captive-bred controls, the argument for a neuro-protective effect of early environmental enrichment against future abnormal behaviors has been made (Lewis et al. 2006). Moreover, studies have shown that dendritic anatomy in young rats was altered in response to a brief 4-day exposure to a complex environment (Wallace et al. 1992) and so was the hippocampus of adult mice in comparison to controls (Kempermann et al. 2002; for more discussion on enrichment see Chapter 4).
Behavioral normalcy is further characterized by the absence of bizarre or atypical patterns of species-specific behavior. Examples of abnormal behavior include excessive barbering observed in mice (Garner et al. 2004; Morton 2002), regurgitation/rumination and coprophagy seen in apes (Nash et al. 1999), or more serious self-injurious behaviors exhibited by rhesus monkeys (Novak 2003). Sometimes, such behaviors represent normal social patterns. For example, coprophagy associated with mother rearing occurs not only in laboratory-housed apes (Nash et al. 1999) but also in the wild where it is postulated to contribute to the reclaiming of unused resources from the feces (Krief et al. 2004). In other cases, however, such patterns are a sign of well-defined diseases or disorders, as, for example, excessive tremors observed in transgenic mice with Huntington’s disease (Mangiarini et al. 1996). In yet other instances, abnormal behavioral patterns, such as stereotypies, may result from suboptimal housing environments (Bayne et al. 1992, 2002; Hubrecht et al. 1992; Mason 1991).
Stereotypic behavior is characterized by highly repetitive and ritualistic actions, the function of which is largely unknown. Environments that elicit or enhance stereotypies not as part of defined pathophysiology or disease models are typically suboptimal (Berkson and Mason 1964; for more references see Additional References). Stereotypies vary across species and appear at different times of day and under different conditions (Mason and Mendl 1997). Classic whole-body stereotypies include circling, pacing (dogs, primates), wall bouncing (dogs), and somersaulting and bar chewing (rodents), whereas self- or other-animal-directed stereotypies often involve the limbs or face and include such patterns as digit sucking, paw licking, and overgrooming (Bayne and Novak 1998; for more references see Additional References).
Although there is yet inadequate research on the relationship between distress and stereotypy, a recent meta-analysis of studies linking stereotypy to animal welfare suggests that some stereotypies may function to regulate arousal and possibly reduce distress as “do-it-yourself enrichment” strategies to alleviate the effect of a suboptimal environment (see Mason and