Narcissistic Personality Disorder (NPD) entails severe impairments in interpersonal functioning that are likely driven by self-beneficial and exploitative behavior. Here, we investigate the underlying motivational and neural mechanisms of prosocial decision-making by experimentally manipulating motivational conflict between self-beneficial and prosocial incentives. One group of patients diagnosed with NPD and a group of healthy controls (CTL) were scanned using functional magnetic resonance imaging while performing a prosocial decision-making task. In this task, we systematically varied the level of conflict between self-beneficial and prosocial options on each trial. We analyzed choice behavior, response times, and neural activity in regions associated with conflict monitoring to test how motivational conflict drives prosocial choice behavior. Participants in the NPD group behaved less prosocially than the CTL group overall. Varying degrees of motivational conflict between self-beneficial and prosocial options induced response variability in both groups, but more so in the CTL group. The NPD group responded faster than the CTL group, unless choosing prosocially, which slowed response times to a level comparable to the CTL group. Additionally, neural activity tracking motivational conflict in dorsomedial prefrontal cortex was reduced in the NPD group. Collectively, low generosity in NPD appears to arise from reduced consideration of prosocial motives, which obviates motivational conflict with self-beneficial motives and entails reduced activity in neural conflict monitoring systems. Yet, our data also indicate that NPD is not marked by an absolute indifference to others’ needs. This points to potentials for improving interpersonal relationships, effectively supporting the well-being of patients and their peers.

自恋型人格障碍 (NPD) 导致人际功能严重受损，这可能是由自利和剥削行为驱动的。在这里，我们通过实验操纵自利和亲社会激励之间的动机冲突来研究亲社会决策的潜在动机和神经机制。一组被诊断患有 NPD 的患者和一组健康对照 (CTL) 在执行亲社会决策任务时使用功能性磁共振成像进行扫描。在这项任务中，我们系统地改变了每次试验中利己和亲社会选择之间的冲突程度。我们分析了与冲突监测相关的区域的选择行为、反应时间和神经活动，以测试动机冲突如何驱动亲社会选择行为。NPD 组参与者的亲社会行为总体上低于 CTL 组。自利和亲社会选择之间不同程度的动机冲突导致两组的反应变异性，但在 CTL 组更是如此。NPD 组的反应比 CTL 组快，除非选择亲社会，这将响应时间减慢到与 CTL 组相当的水平。此外，NPD 组的背内侧前额叶皮层的神经活动追踪动机冲突有所减少。总的来说，NPD 的低慷慨度似乎是由于减少了对亲社会动机的考虑，这避免了动机冲突与自利动机，并导致神经冲突监测系统的活动减少。然而，我们的数据还表明，NPD 的特点并不是对他人的需求绝对漠不关心。