Wisconsin Card Sorting Test with macaque monkeys

The Wisconsin Card Sorting Task (WCST) is a clinical test that is highly sensitive to damage in the prefrontal cortex. To establish an animal model in which neural bases of the cognitive functions necessary for the execution of the WCST can be examined with a variety of neuroscience methods, we trained two macaque monkeys in a version of the WCST with two dimensions. A sample had to be matched with one of three test items by either matching in color or shape. The monkeys had to find the relevant sensory dimension and to detect sudden changes in matching rules based only on reward and error signals. Both monkeys succeeded in more than 10 rule shifts within a day. Several probe tests showed that the monkeys in fact used the dimension-based matching rules. Each rule shift was generalized from the experience of some samples to all of the others in the sample set, and rules were immediately applied to newly introduced samples. The frequent shifts could be overcome only with a representation of the sensory dimension in working memory. Thus, we have established an animal model in which the relevant sensory dimension is stored in working memory, updated by assessing behavioral outcomes, and used to guide matching behavior.