Differential Effects of Amygdala, Orbital Prefrontal Cortex, and Prelimbic Cortex Lesions on Goal-Directed Behavior in Rhesus Macaques
We assessed the involvement of the orbital prefrontal cortex (PFo), the prelimbic region of the medial prefrontal cortex (PL), and the amygdala in goal-directed behavior. Rhesus monkeys were trained on a task in which two different instrumental responses were linked to two different outcomes. One response, called “tap,” required the monkeys to repeatedly touch a colored square on a video monitor to produce one kind of food reward. The other response, called “hold,” required persistent contact of an identical stimulus, and it produced a different kind of food reward. After training, we assessed the effects of sensory-specific reinforcer devaluation as a way to probe each monkey's use of goal-directed behavior. In this procedure, monkeys were allowed to consume one of the two foods to satiety and were then tested for tap/hold preference under extinction. Unoperated control monkeys showed a reduction in the response associated with obtaining the devalued food, called the “devaluation effect,” a hallmark of goal-directed behavior. Monkeys with bilateral lesions of PFo or the amygdala exhibited significantly reduced devaluation effects. Results from monkeys with PL lesions were equivocal. We conclude that both PFo and the amygdala play a significant role in goal-directed behavior in monkeys. Notably, the findings for PFo challenge the idea that orbital and medial prefrontal regions are exclusively dedicated to object- and action-based processes, respectively.