Neural Substrates of Reward Processing and Emotion

病变研究表明内侧前额叶皮层（MFC）和眶额皮层（OFC）的功能是分离的，MFC对社会认知至关重要，OFC对基于价值的决策至关重要。虽然双侧杏仁核损伤也会导致这些领域的损伤，但尚不清楚MFC和OFC的可分离功能作用是否严重依赖于与杏仁核的相互作用。为了测试这种可能性，我们比较了动物的表现与交叉手术断开的前边缘皮质，一个亚区的MFC，和杏仁核（MFC x AMY）和动物手术断开的OFC和杏仁核（OFC x AMY），一组控制（CON）。所有动物在观看社会刺激视频（社会兴趣测试）和基于当前食物价值的物体选择（贬值任务，基于价值的决策测试）时评估食物检索延迟。与CON组相比，MFC x AMY组，而不是OFC x AMY组，在同种视频的存在下，表现出显著减少的延迟以获得奖励，这表明社会价值降低和/或社会兴趣降低。然而，在一项基于价值的决策测试中，观察到了相反的模式; OFC x AMY组，而不是MFC x AMY组，在选择性饱足后，在对象选择上表现出严重的缺陷。这些数据表明，MFC和OFC与杏仁核相互作用，分别在社会评价和对象评价领域中做出不同的行为贡献。这些前额叶-杏仁核回路在功能上是分离的，这支持了MFC和OFC对环境的认知评价做出独立贡献的观点。 如上所述，MFC与杏仁核和颞顶交界处附近的皮质一起参与社会认知。这个大脑区域网络专门用于处理社会信息。例如，MFC中的神经元不仅编码奖励值，还编码同种和自身的特征。 我们之前的研究已经证明，MFC损伤会削弱亲社会偏好的学习。然而，很难理清MFC对社会注意力、社会偏好和社会奖励的贡献，如通过替代强化（即，愿为他人奉献自己）。为了进一步研究MFC在社会认知中的作用，我们测量了MFC损伤对动物观看具有社会（同种面孔）或非社会（无生命物体）内容的图像偏好的影响。完整的动物和MFC损伤的动物都被允许在两个中性的先行刺激之间进行选择：一个预测社会形象的出现，另一个预测非社会形象的出现。所有的动物都表现出轻微的，但统计上显着的偏好选择的先行词预测社会形象。MFC损伤并没有减少观看社会形象的偏好，然而，动物与MFC病变往往使更多的期待在先行刺激之前，作出选择相比，控制。这些研究结果表明，MFC损伤的动物比对照组更难评估与社会结果相关的故意行为，但评估社会刺激本身的内在价值没有困难。

Lesion studies suggest dissociable functions of medial prefrontal cortex (MFC) and orbitofrontal cortex (OFC), with MFC being essential for social cognition and OFC being essential for value-based decision making. Although bilateral amygdala damage also results in impairments in these domains, it is not known whether the dissociable functional roles of MFC and OFC critically depend on interactions with the amygdala. To test this possibility, we compared the performance of animals with crossed surgical disconnection of the prelimbic cortex, a subregion of MFC, and amygdala (MFC x AMY) and animals with surgical disconnection of the OFC and amygdala (OFC x AMY), to a group of controls (CON). All animals were assessed for food-retrieval latency while viewing videos of social stimuli (a test of social interest) and object choices based on current food value (devaluation task, a test of value-based decision making). Compared to the CON group, group MFC x AMY, but not group OFC x AMY, showed significantly reduced latencies to reach for a reward in the presence of videos of conspecifics, indicating reduced social valuation and/or reduced social interest. In a test of value-based decision making, however, the opposite pattern was observed; group OFC x AMY, but not group MFC x AMY, displayed severe deficits on object choice following selective satiation. These data indicate that MFC and OFC interact with the amygdala to subserve distinct behavioral contributions in the domains of social valuation and object valuation, respectively. That these prefrontal-amygdala circuits are functionally dissociable lends support to the idea that MFC and OFC make independent contributions to cognitive appraisals of the environment. As indicated above, the MFC, together with the amygdala and cortex near the temporal-parietal junction is implicated in social cognition. This network of brain regions is specialized for processing social information. For example, neurons in the MFC encode not only reward value but also features of conspecifics and of oneself. Our previous research has demonstrated that MFC damage blunts learning of prosocial preferences. It has been difficult, however, to disentangle MFC contributions to social attention, social preference, and social reward, as measured by vicarious reinforcement (i.e., the willingness to give reward to others). To further investigate the role of the MFC in social cognition, we measured the influence of MFC damage on animals preferences for viewing images with social (conspecific faces) or nonsocial (inanimate objects) content. Both intact animals and those with MFC damage were allowed to choose between two neutral antecedent stimuli: one predicting the onset of a social image and the other predicting the onset of a nonsocial image. All animals exhibited a slight but statistically significant preference for choosing the antecedent that predicted social images. MFC damage did not reduce preferences for viewing social images; however, animals with MFC lesions tended to make more looks at the antecedent stimuli before making a choice compared to controls. These findings suggest that animals with MFC damage experience greater difficulty than controls evaluating deliberate actions associated with social outcomes but have no difficulty assessing the inherent value of social stimuli per se.