Rhesus monkeys with orbital prefrontal cortex lesions can learn to inhibit prepotent responses in the reversed reward contingency task

Monkeys with lesions of the orbital prefrontal cortex (PFo) are impaired on behavioral tasks that require the ability to respond flexibly to changes in reward contingency (e.g., object reversal learning and extinction). These and related findings in rodents and humans have led to the suggestion that PFo is critical for the inhibitory control needed to overcome prepotent responses. To test this idea, we trained rhesus monkeys with PFo lesions and unoperated controls on acquisition of the reversed reward contingency task. In this task, selecting the smaller of 2 food quantities (1 half peanut [1P]) leads to receipt of the larger quantity (4 half peanuts [4P]) and vice versa. Choice of a larger quantity of food is a reliable prepotent response, and, accordingly, all monkeys initially selected 4P rather than one. With experience, however, all monkeys learned to select 1P in order to receive 4. Surprisingly, monkeys with PFo lesions learned as quickly as unoperated controls. Thus, PFo lesions do not yield a deficit in all tests that require the inhibition of a prepotent response.