Developing a Rat Model of Transitive Behavior
Karen Lionello-Denolf

Funded by NIH, R21 MH067801

Stimulus equivalence reflects the ability to classify/categorize stimuli on the basis of shared contingency-defined relations that are not based on physical features. The capacity for stimulus equivalence may be a necessary prerequisite for symbolic functioning. Monkeys, chimpanzees, and sea lions can display some of the emergent relations that document empirically the existence of equivalence classification: reflexivity, symmetry, and transitivity. Of these relations, transitivity is the most complex behaviorally; it demonstrates the ability to infer a relation between two stimuli given that both are related to a third stimulus. A positive outcome on transitivity tests may indicate the potential for symbolic functioning in the absence of language, a theoretical position with profound implications for understanding how cognition relates to the development of communicative behavior. A small number of studies have suggested that rats also are capable of exhibiting transitivity; however, certain methodological issues raise questions about the proper interpretation of these findings. We have developed a paradigm for rats to circumvent methodological concerns so that a practical laboratory animal model of transitivity can be established and elaborated for future research. Rats will be trained in an automated nosepoke apparatus to develop two arbitrary stimulus classes. A matching-to-sample task using six olfactory stimuli will be used to teach explicitly some of the possible stimulus pairs within a class; e.g., match A to B and then B to C. If rats have developed emergent transitivity, then they should show high accuracy on probe trials for matching A to C, the untaught stimulus pair. Rats are expected to display transitive behavior. If they do, certain future research directions will be suggested that would proceed logically from the results.

Ultimately, this rat model could lead to advances in the assessment of non-language based symbolic behavior, and to applications in the study of topics such as behavioral toxicology and animal models of intellectual disabilities.