Department of Experimental Psychology, Ghent University, 9000 Ghent, Belgium.
J Neurosci. 2011 Mar 30;31(13):4955-61. doi: 10.1523/JNEUROSCI.4845-10.2011.
Dopamine release in cortical and subcortical structures plays a central role in reward-related neural processes. Within this context, dopaminergic inputs are commonly assumed to play an activating role, facilitating behavioral and cognitive operations necessary to obtain a prospective reward. Here, we provide evidence from human fMRI that this activating role can also be mediated by task-demand-related processes and thus extends beyond situations that only entail extrinsic motivating factors. Using a visual discrimination task in which varying levels of task demands were precued, we found enhanced hemodynamic activity in the substantia nigra (SN) for high task demands in the absence of reward or similar extrinsic motivating factors. This observation thus indicates that the SN can also be activated in an endogenous fashion. In parallel to its role in reward-related processes, reward-independent activation likely serves to recruit the processing resources needed to meet enhanced task demands. Simultaneously, activity in a wide network of cortical and subcortical control regions was enhanced in response to high task demands, whereas areas of the default-mode network were deactivated more strongly. The present observations suggest that the SN represents a core node within a broader neural network that adjusts the amount of available neural and behavioral resources to changing situational opportunities and task requirements, which is often driven by extrinsic factors but can also be controlled endogenously.
皮质和皮质下结构中的多巴胺释放在与奖励相关的神经过程中起着核心作用。在这种情况下，多巴胺能输入通常被认为起着激活作用，促进获得预期奖励所需的行为和认知操作。在这里，我们提供了来自人类 fMRI 的证据，表明这种激活作用也可以通过与任务需求相关的过程来介导，因此超出了仅涉及外在激励因素的情况。使用一个视觉辨别任务，其中预先提示了不同水平的任务需求，我们发现，在没有奖励或类似外在激励因素的情况下，高任务需求会增强黑质（SN）的血液动力学活动。因此，这一观察表明 SN 也可以以内在的方式被激活。与它在与奖励相关的过程中的作用并行，与奖励无关的激活可能有助于招募满足增强的任务需求所需的处理资源。与此同时，皮质和皮质下控制区域的广泛网络的活动对高任务需求增强，而默认模式网络的区域则更强烈地去激活。目前的观察结果表明，SN 代表了一个更广泛的神经网络中的核心节点，该网络根据不断变化的情境机会和任务要求调整可用神经和行为资源的数量，这通常是由外在因素驱动的，但也可以被内在控制。
