Institut de Neurosciences de la Timone, CNRS-Université Aix-Marseille, UMR 7289, 13385 Marseille Cedex 5, France.
J Neurosci. 2012 Oct 31;32(44):15359-68. doi: 10.1523/JNEUROSCI.1768-12.2012.
Motor cortical neurons are activated during movement preparation and execution, and in response to task-relevant visual cues. A few studies also report activation before the expected presentation of cues. Here, we study specifically this anticipatory activity preceding visual cues in motor cortical areas. We recorded the activity of 1215 neurons in the motor cortex of two macaque monkeys while they performed a center-out reaching task, including two consecutive delays of equal duration, known in advance. During the first delay (D1), they had to await the spatial cue and only reach to the cued target after the second delay (D2). Forty-two percent of the neurons displayed anticipatory activity during D1. Among these anticipatory neurons, 59% increased (D1up) their activity and the remaining decreased (D1down) their activity. By classifying the neurons according to these firing rate profiles during D1, we found that the activity during D2 differed in a systematic way. The D1up neurons were more likely to discharge phasically soon after the spatial cue and were less active during movement execution, whereas the D1down neurons showed the opposite pattern. But, regardless of their temporal activity profiles, the two categories seemed equally involved in early and late motor preparation, as reflected in their directional selectivity. This precue activity in motor cortex may reflect two complementary, coexisting processes: the facilitation of incoming spatial information in parallel with the downregulation of corticospinal excitability to prevent a premature response.
运动皮层神经元在运动准备和执行期间以及对任务相关视觉线索的反应中被激活。一些研究还报告了在预期线索出现之前的激活。在这里，我们专门研究运动皮层区域中视觉线索之前的这种预期活动。我们记录了两只猕猴运动皮层中 1215 个神经元的活动，它们在执行中心到外周的伸展任务时，包括两个已知的相等持续时间的连续延迟。在第一个延迟（D1）期间，他们必须等待空间线索，只有在第二个延迟（D2）后才能到达提示目标。42%的神经元在 D1 期间表现出预期活动。在这些预期神经元中，59%的神经元增加（D1up）了它们的活动，而其余的神经元减少（D1down）了它们的活动。通过根据 D1 期间的这些放电率曲线对神经元进行分类，我们发现 D2 期间的活动以系统的方式不同。D1up 神经元在空间线索后很快就会呈现相位放电，并且在运动执行期间的活动较少，而 D1down 神经元则呈现相反的模式。但是，无论它们的时间活动曲线如何，这两类神经元似乎都同样参与了早期和晚期运动准备，这反映在它们的方向选择性上。运动皮层中的这种预线索活动可能反映了两种互补的、共存的过程：平行促进传入的空间信息，同时下调皮质脊髓兴奋性以防止过早反应。
