Biomedical Engineering Program, University of Colorado, Boulder, Colorado, United States.
Integrative Physiology Department, University of Colorado, Boulder, Colorado, United States.
J Neurophysiol. 2024 Nov 1;132(5):1395-1411. doi: 10.1152/jn.00040.2024. Epub 2024 Sep 25.
How the brain decides when to invest effort is a central question in neuroscience. When asked to walk a mile to a destination, would you choose a path with a hill at the beginning or the end? The traditional view of effort suggests we should be indifferent-all joules are equal so long as it does not interfere with accomplishing the goal. Yet, when total joules are equal across movement decisions, the brain's sensitivity to the temporal profile of effort investment remains poorly understood. Here, we sought to parse the interaction of time and physical effort by comparing subjective preferences in an isometric arm-pushing task that varied the duration and timing of high and low effort. Subjects were presented with a series of two-alternative forced choices, where they chose the force profile they would rather complete. Subjects preferred earlier physical effort (i.e., to precrastinate) but were idiosyncratic about preference for task timing. A model of subjective utility that includes physical effort costs, task costs, and independent temporal sensitivity factors described subject preferences best. Interestingly, deliberation time and response vigor covary with the same subjective utility model for preference, suggesting a utility that underlies both decision making and motor control. These results suggest physical effort costs are temporally sensitive, with earlier investment of effort preferred to later investment, and that the representation of effort is based on not only the total energy required but also when it is required to invest that energy. We use a novel paradigm that differentiates physical effort costs, task costs, and time, where subjects choose between isometric arm-pushing tasks. Subjects prefer high physical effort earlier than later. They also decide faster and respond more vigorously the greater their preference. We find a generalizable subjective utility model that includes independent time-sensitivity of physical effort and task costs. Together, we demonstrate that subjective effort includes not only the total effort invested but also its timing.
大脑何时决定投入努力是神经科学的一个核心问题。当被要求走一英里到一个目的地时，你会选择一开始就有一个山丘的路径还是最后有一个山丘的路径？传统的努力观点表明，我们应该漠不关心——只要它不干扰目标的实现，所有焦耳都是平等的。然而，当总焦耳在运动决策中相等时，大脑对努力投入的时间分布的敏感性仍然知之甚少。在这里，我们通过比较等长手臂推动任务中时间和体力努力的相互作用，试图解析时间和体力努力的相互作用，该任务改变了高努力和低努力的持续时间和时间安排。受试者接受了一系列的二选一强制选择，在这些选择中，他们选择了他们宁愿完成的力量分布。受试者更喜欢早期的体力努力（即提前完成），但对任务时间的偏好却因人而异。一个包括体力努力成本、任务成本和独立时间敏感因素的主观效用模型最好地描述了受试者的偏好。有趣的是，思考时间和反应活力与偏好的相同主观效用模型相关，这表明了一种决策和运动控制的基础效用。这些结果表明体力努力成本是时间敏感的，早期的努力投入比后期的努力投入更受欢迎，并且努力的表示不仅基于所需的总能量，还基于何时需要投入该能量。我们使用了一种新颖的范式，该范式区分了体力努力成本、任务成本和时间，其中受试者在等长手臂推动任务之间进行选择。受试者更喜欢早期的高体力努力，而不是后期的高体力努力。他们也会更快地做出决定，反应更有力，因为他们的偏好更强烈。我们发现了一个可推广的主观效用模型，其中包括体力努力和任务成本的独立时间敏感性。总的来说，我们证明了主观努力不仅包括投入的总努力，还包括其时间分布。
