Mizes Kevin G C, Lindsey Jack, Escola G Sean, Ölveczky Bence P
Program in Biophysics, Harvard University, Cambridge, MA, USA.
Department of Organismic and Evolutionary Biology and Center for Brain Science, Harvard University, Cambridge, MA, USA.
Nat Neurosci. 2024 Dec;27(12):2466-2475. doi: 10.1038/s41593-024-01792-3. Epub 2024 Nov 4.
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存在广泛争议，各项研究支持不同观点。在此，我们探究运动皮层的参与程度在多大程度上取决于任务需求，具体而言，其作用在高度熟练的或“自动的”序列与由外部线索引导的灵活序列之间是否有所不同。为了验证这一点，我们训练大鼠生成三元素运动序列，方法是让它们对单一序列进行过度训练，或者让它们遵循指导性视觉线索。损毁运动皮层表明，它对于灵活的线索驱动运动序列是必要的，但对于单独训练的单一自动行为则是可有可无的。然而，当自动运动序列与灵活任务一起训练时，它就变得依赖运动皮层了，这表明当相同序列也在灵活情境中产生时，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再现了这些结果，并提供了一个回路层面的解释。我们的结果明确界定了运动皮层在运动序列执行中的作用，描述了其参与的条件及其履行的功能，从而调和了关于运动皮层在运动序列生成中作用的看似相互矛盾的观点。
