The role of the motor cortex in executing motor sequences is widely debated, with studies supporting disparate views. Here we probe the degree to which the motor cortex’s engagement depends on task demands, specifically whether its role differs for highly practiced, or ‘automatic’, sequences versus flexible sequences informed by external cues. To test this, we trained rats to generate three-element motor sequences either by overtraining them on a single sequence or by having them follow instructive visual cues. Lesioning motor cortex showed that it is necessary for flexible cue-driven motor sequences but dispensable for single automatic behaviors trained in isolation. However, when an automatic motor sequence was practiced alongside the flexible task, it became motor cortex dependent, suggesting that an automatic motor sequence fails to consolidate subcortically when the same sequence is produced also in a flexible context. A simple neural network model recapitulated these results and offered a circuit-level explanation. Our results critically delineate the role of the motor cortex in motor sequence execution, describing the conditions under which it is engaged and the functions it fulfills, thus reconciling seemingly conflicting views about motor cortex’s role in motor sequence generation.

运动皮层在执行运动序列中的作用受到广泛争论，研究支持不同的观点。在这里，我们探讨了运动皮层的参与在多大程度上取决于任务需求，特别是它的作用是否不同于高度练习或“自动”的序列与由外部线索告知的灵活序列。为了测试这一点，我们训练大鼠通过在单个序列上过度训练或让它们遵循有指导性的视觉线索来生成三元素运动序列。损伤运动皮层表明，它对于灵活的线索驱动的运动序列是必需的，但对于孤立训练的单一自动行为来说是可有可无的。然而，当自动运动序列与柔性任务一起练习时，它变得依赖于运动皮层，这表明当在柔性环境中产生相同的序列时，自动运动序列无法在皮层下巩固。一个简单的神经网络模型概括了这些结果，并提供了电路级的解释。我们的结果批判性地描述了运动皮层在运动序列执行中的作用，描述了它参与的条件和它所实现的功能，从而调和了关于运动皮层在运动序列生成中的作用的看似冲突的观点。