Representation of Functional Category in the Monkey Prefrontal Cortex and Its Rule-Dependent Use for Behavioral Selection

Humans, monkeys, and other animals are considered to have the cognitive ability to use functional categories—that is, stimulus groups based on functional equivalence independent of physical properties. To investigate the underlying neural mechanisms of the use of functional categories, we recorded single-unit activity in the prefrontal cortex of monkeys performing a behavioral task in which the rule-dependent usage of functional category was needed to select an appropriate response. We found a neural correlate of functional categories on the single-neuron level and found that category information is coded independently of other task-relevant information such as rule and contingency information. Analysis of the time course of the information activation suggested that contingency information used for action selection is derived by integrating incoming category information with rule information maintained throughout a session. Such neural computation can be considered as the neural background of flexible behavioral control based on category and rule. SIGNIFICANCE STATEMENT Perceptual categories are based on perceptual similarity, whereas functional categories are based on functional equivalence independently of their physical properties. The neural background of perceptual categories has been investigated in a number of studies, but that of functional categories has been investigated in only a few. In the present study, we found neural correlates of functional categories on the single-neuron level. Further analysis suggested that functional category information and rule information is integrated within the prefrontal cortex to derive contingency information necessary for action selection. This study has shown how the brain uses the category to select an action appropriate to the behavioral context.