Department of Psychology and Behvaioural and Clinical Neuroscience Institute, University of Cambridge, Cambridge, UK.
Erl Wood Manor, Eli Lilly & Co Ltd, Windlesham, UK.
Eur J Neurosci. 2018 Nov;48(9):2971-2987. doi: 10.1111/ejn.14150. Epub 2018 Sep 28.
Goal-directed motivated behaviour is crucial for everyday life. Such behaviour is often measured, in rodents, under a progressive ratio (PR) schedule of reinforcement. Previous studies have identified a few brain structures critical for supporting PR performance. However, the association between neural activity within these regions and individual differences in effort-related behaviour is not known. Presently, we used constant potential in vivo oxygen amperometry, a surrogate for functional resonance imaging in rodents, to assess changes in tissue oxygen levels within the nucleus accumbens (NAc) and orbitofrontal cortex (OFC) in male Wistar rats performing a PR task. Within both regions, oxygen responses to rewards increased as the effort exerted to obtain the rewards was larger. Furthermore, higher individual breakpoints were associated with greater magnitude NAc oxygen responses. This association could not be explained by temporal confounds and remained significant when controlling for the different number of completed trials. Animals with higher breakpoints also showed greater magnitude NAc oxygen responses to rewards delivered independently of any behaviour. In contrast, OFC oxygen responses were not associated with individual differences in behavioural performance. The present results suggest that greater NAc oxygen responses following rewards, through a process of incentive motivation, may allow organisms to remain on task for longer and to overcome greater effort costs.
目标导向的动机行为对于日常生活至关重要。这种行为通常在啮齿动物中通过递增比率（PR）强化时间表来测量。以前的研究已经确定了一些对支持 PR 表现至关重要的大脑结构。然而，这些区域内的神经活动与努力相关行为的个体差异之间的关联尚不清楚。目前，我们使用恒电位活体氧安培术（一种啮齿动物功能磁共振成像的替代方法）来评估雄性 Wistar 大鼠在执行 PR 任务时，其伏隔核（NAc）和眶额皮质（OFC）中的组织氧水平的变化。在这两个区域中，随着获得奖励所付出的努力增加，氧气对奖励的反应也会增加。此外，个体断点越高，NAc 氧气反应的幅度越大。这种关联不能用时间上的混淆来解释，并且在控制不同完成试验数量时仍然具有统计学意义。断点较高的动物对独立于任何行为的奖励的 NAc 氧气反应幅度也更大。相比之下，OFC 的氧气反应与行为表现的个体差异无关。本研究结果表明，奖励后 NAc 氧气反应的增加（通过激励动机的过程）可能使生物体能够更长时间地保持任务状态，并克服更大的努力成本。
