Coding and monitoring of motivational context in the primate prefrontal cortex.

The prefrontal cortex is involved in acquiring and maintaining information about context, including the set of task instructions and/or the outcome of previous stimulus-response sequences. Most studies on context-dependent processing in the prefrontal cortex have been concerned with such executive functions, but the prefrontal cortex is also involved in motivational operations. We thus wished to determine whether primate prefrontal neurons show evidence of representing the motivational context learned by the monkey. We trained monkeys in a delayed reaction task in which an instruction cue indicated the presence or absence of reward. In random alternation with no reward, the same one of several different kinds of food and liquid rewards was delivered repeatedly in a block of approximately 50 trials, so that reward information would define the motivational context. In response to an instruction cue indicating absence of reward, we found that neurons in the lateral prefrontal cortex not only predicted the absence of reward but also represented more specifically which kind of reward would be omitted in a given trial. These neurons seem to code contextual information concerning which kind of reward may be delivered in following trials. We also found prefrontal neurons that showed tonic baseline activity that may be related to monitoring such motivational context. The different types of neurons were distributed differently along the dorsoventral extent of the lateral prefrontal cortex. Such operations in the prefrontal cortex may be important for the monkey to maximize reward or to modify behavioral strategies and thus may contribute to executive control.