The trade-off between effort and reward is one of the main determinants of behavior, and its alteration is at the heart of major disorders such as depression or Parkinson’s disease. Monoaminergic neuromodulators are thought to play a key role in this trade-off, but their relative contribution remains unclear. Rhesus monkeys (Macaca mulatta) performed a choice task requiring a trade-off between the volume of fluid reward and the amount of force to be exerted on a grip. In line with a causal role of noradrenaline in effort, decreasing noradrenaline levels with systemic clonidine injections (0.01 mg/kg) decreased exerted force and enhanced the weight of upcoming force on choices, without any effect on reward sensitivity. Using computational modeling, we showed that a single variable (“effort”) could capture the amount of resources necessary for action and control both choices (as a variable for decision) and force production (as a driving force). Critically, the multiple effects of noradrenaline manipulation on behavior could be captured by a specific modulation of this single variable. Thus, our data strongly support noradrenaline’s implication in effort processing.

努力和回报之间的权衡是行为的主要决定因素之一，其改变是抑郁症或帕金森病等重大疾病的核心。单胺能神经调节剂被认为在这种权衡中发挥着关键作用，但它们的相对贡献仍不清楚。恒河猴（Macaca mulatta）执行一项选择任务，需要在液体奖励量和抓握力之间进行权衡。与去甲肾上腺素在努力中的因果作用一致，通过全身注射可乐定（0.01 mg/kg）降低去甲肾上腺素水平可以减少所用的力量并增加即将到来的选择力量的重量，而对奖励敏感性没有任何影响。使用计算模型，我们表明单个变量（“努力”）可以捕获行动所需的资源量，并控制选择（作为决策变量）和力量生产（作为驱动力）。至关重要的是，去甲肾上腺素操纵对行为的多重影响可以通过对这个单一变量的特定调节来捕获。因此，我们的数据强烈支持去甲肾上腺素在努力处理中的作用。