Izquierdo Alicia, Suda Robin K, Murray Elisabeth A
Section on the Neurobiology of Learning and Memory, Laboratory of Neuropsychology, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland 20892-4415, USA.
J Neurosci. 2004 Aug 25;24(34):7540-8. doi: 10.1523/JNEUROSCI.1921-04.2004.
The orbital prefrontal cortex (PFo) operates as part of a network involved in reward-based learning and goal-directed behavior. To test whether the PFo is necessary for guiding behavior based on the value of expected reward outcomes, we compared four rhesus monkeys with two-stage bilateral PFo removals and six unoperated controls for their responses to reinforcer devaluation, a task that assesses the monkeys' abilities to alter choices of objects when the value of the underlying food has changed. For comparison, the same monkeys were tested on a standard test of flexible stimulus-reward learning, namely object reversal learning. Relative to controls, monkeys with bilateral PFo removals showed a significant attenuation of reinforcer devaluation effects on each of two separate assessments, one performed shortly after surgery and the other approximately 19 months after surgery; the operated monkeys were also impaired on object reversal learning. The same monkeys, however, were unimpaired in acquisition of object discrimination learning problems and responded like controls when allowed to choose foods alone, either on a food preference test among six different foods or after selective satiation. Thus, satiety mechanisms and the ability to assign value to familiar foods appear to be intact in monkeys with PFo lesions. The pattern of results suggests that the PFo is critical for response selection based on predicted reward outcomes, regardless of whether the value of the outcome is predicted by affective signals (reinforcer devaluation) or by visual signals conveying reward contingency (object reversal learning).
眶额前皮质（PFo）作为参与基于奖励的学习和目标导向行为的网络的一部分发挥作用。为了测试PFo对于基于预期奖励结果的价值来指导行为是否必要，我们比较了四只接受双侧PFo切除的恒河猴和六只未手术的对照猴对强化物贬值的反应，这是一项评估猴子在潜在食物价值发生变化时改变物体选择能力的任务。为了进行比较，对相同的猴子进行了灵活刺激-奖励学习的标准测试，即物体反转学习。相对于对照猴，双侧PFo切除的猴子在两项单独评估中的每一项中，强化物贬值效应都显著减弱，一项在手术后不久进行，另一项在手术后约19个月进行；手术猴在物体反转学习中也受损。然而，相同的猴子在物体辨别学习问题的习得方面未受损，并且在单独选择食物时，无论是在六种不同食物的食物偏好测试中还是在选择性饱足后，其反应都与对照猴相似。因此，饱足机制以及为熟悉食物赋予价值的能力在PFo损伤的猴子中似乎是完整的。结果模式表明，PFo对于基于预测奖励结果的反应选择至关重要，无论结果的价值是由情感信号（强化物贬值）还是由传达奖励偶然性的视觉信号（物体反转学习）预测的。
