Kashefi Mehrdad, Diedrichsen Jörn, Pruszynski J Andrew
Western Center for Brain and Mind, Western University, London, Ontario N6A 3K7, Canada.
Departments of Statistical and Actuarial Sciences, Western University, London, Ontario N6A 3K7, Canada.
J Neurosci. 2025 Aug 13;45(33):e0299252025. doi: 10.1523/JNEUROSCI.0299-25.2025.
Learning new sequential movements is a fundamental skill for many animals. Motor sequence learning may arise from three distinct processes: (1) improved execution of individual movements independent of their sequential context; (2) enhanced anticipation of "what" movement should be executed next, enabling faster initiation; and (3) the development of motoric sequence-specific representations that encode "how" movements should be optimally performed within a sequence. However, many existing paradigms conflate the "what" and "how" components of learning, as participants often acquire both the sequence content (what to do) and its execution (how to do it). This overlap obscures the distinct contributions of each mechanism to motor sequence learning. In this study, we disentangled these mechanisms in a continuous reaching task by varying how many upcoming targets were visible. When participants ( = 14, 8F) could only see one future target, improvements were mostly due to them learning which target would come next. When they could see four future targets, participants immediately demonstrated faster movement times and increased movement smoothness, surpassing late-stage performance in the one-target condition. Crucially, even with full visibility of future targets, participants showed further sequence-specific learning driven by a continuous optimization of movement trajectories. Follow-up experiments ( = 42, 21F) revealed that the learned sequence representations did not generalize in extrinsic coordinates across limbs and encoded contextual information of four movements or longer. Our paradigm dissociates between the "what" and "how" components of motor sequence learning and provides evidence for the development of motoric sequence representations that guide optimal movement execution.
学习新的连续动作是许多动物的一项基本技能。运动序列学习可能源于三个不同的过程：（1）独立于其连续背景的单个动作执行的改善；（2）对接下来应执行“什么”动作的增强预期，从而实现更快的启动；（3）运动序列特定表征的发展，该表征编码在一个序列中动作应如何最佳执行。然而，许多现有的范式将学习的“什么”和“如何”成分混为一谈，因为参与者通常既获取了序列内容（做什么）又获取了其执行方式（如何做）。这种重叠掩盖了每种机制对运动序列学习的不同贡献。在本研究中，我们通过改变可见的即将到来的目标数量，在连续伸手任务中区分了这些机制。当参与者（n = 14，8名女性）只能看到一个未来目标时，改善主要是因为他们了解了接下来会出现哪个目标。当他们能看到四个未来目标时，参与者立即表现出更快的运动时间和更高的运动流畅性，超过了单目标条件下的后期表现。至关重要的是，即使未来目标完全可见，参与者也通过运动轨迹的持续优化表现出进一步的序列特定学习。后续实验（n = 42，21名女性）表明，所学的序列表征不会在外在坐标中跨肢体泛化，并且编码了四个或更长动作的上下文信息。我们的范式区分了运动序列学习的“什么”和“如何”成分，并为指导最佳动作执行的运动序列表征的发展提供了证据。
