Animal models of obsessive-compulsive disorder may be derived naturally or generated experimentally. Either may be considered a full or partial model, depending on the extent of resemblance to human OCD. Although many models appear to be valid at first glance, complete models should demonstrate “compelling similarities” in all areas examined. Partial models may have only one or two OCD-like features; however, they still provide some opportunities for research. Criteria to consider when evaluating potential models are etiology, symptomatology, and use in indicating methods of therapy and prevention. Demonstration of common underlying physiological mechanisms, patterns of development and expression, and familial associations are some specific elements to consider when assessing the relevance of more complete models.
Cognitive aspects of OCD are difficult, if not impossible, to explore in animals at present and may be quite different from what is found in humans. It is hard to imagine that animals experience ego-dystonicity; however, dogs with acral lick dermatitis (ALD) that have been scolded by their owners will resort to licking themselves when out of sight, implying that they know it is wrong. Because of the difficulty in evaluating an animal's internal state, some adopt the position that there is no complete animal model of OCD and that animal models are at best partial models. However, children who exhibit compulsive behaviors frequently do not experience accompanying obsessions. Even the expression of OCD in children—for example, licking and walking in geometric designs—resembles what is seen in animals.
In the descriptions that follow, only directly comparable aspects of compulsive behavior in animals will be discussed. Naturally occurring models that appear to correspond most closely to full models may be useful in understanding the fundamental mechanisms underlying OCD and the OC spectrum, including genetics and neurobiology. Experimental models, which may be either full or partial models, could contribute similarly or provide limited but specific information in a targeted area of study, depending on the extent of their similarity to OCD.