What language does the motor cortex use to speak to motoneurons?

描述(申请人提供)：运动皮质使用什么语言与运动神经元交谈？初级运动皮质(M1)是脊髓下行指令的主要来源，用于产生运动输出。额叶皮质脊髓神经元中约有50%起源于M1。一组特殊的皮质脊髓神经元是皮质连神经(CM细胞)，它与运动神经元有直接联系。我们将结合行为学、电生理学和解剖学的方法来研究CM细胞。我们建议，第一次，提供一个明确和一致的观点，从CM细胞到运动神经元的信号。我们将使用肌电(EMG)活动的尖峰触发平均(SPTA)来识别CM细胞及其靶肌肉。CM细胞及其目标肌肉的活动将与多方向手腕任务中涉及的手腕运动有关，该多向手腕任务能够分离手腕运动的内在(肌肉样)和外在(运动样)参数。以前的研究表明，M1活动中既有内在参数，也有外在参数(Kakei等人，1999)。解释“肌肉”和“运动”同时存在的一种方式是存在等级。层次假说认为CM细胞的活动类似于肌肉，而非CM细胞的活动类似于运动。换句话说，运动神经元的直接输入是一种不需要翻译的语言。另一种选择是，肌肉样活动和运动样活动的混合体到达运动神经元，用于在不同条件下创造动作。这个项目将决定哪一种假设是正确的。我们还将首次记录投射到腕肌运动神经元的CM细胞的位置和分布。我们将利用狂犬病病毒的跨神经元运输来确定CM细胞在运动皮质中的位置，这些细胞影响对抗手腕肌；腕屈肌和桡侧腕伸肌。如果时间允许，我们将比较幼稚动物和训练有素的动物手腕上CM细胞的分布。这项实验将使我们能够确定广泛的训练是否改变了M1中CM细胞的皮质区域。

DESCRIPTION (provided by applicant): What language does the motor cortex use to speak to motoneurons? The primary motor cortex (M1) is a major source of descending commands to the spinal cord for generating motor output. Approximately 50% of the corticospinal neurons from the frontal lobe originate from M1. A special set of these corticospinal neurons are corticomotoneural (CM cells) which have direct connections to motoneurons. We will investigate CM cells using a combination of behavioral, electrophysiological and anatomical methods. We propose to provide, for the first time, a clear and consistent view of signaling from CM cells to motoneurons. We will identify CM cells and their target muscles using spike-triggered averaging (SpTA) of electromyographic (EMG) activity. The activity of CM cells and their target muscles will be investigated in relation to wrist movements involved in a multi-directional wrist task capable of dissociating intrinsic (muscle-like) and extrinsic (movement-like) parameters of wrist movement. Previous studies have shown that both intrinsic and extrinsic parameters are present in M1 activity (Kakei et al., 1999). One way to explain the presence of both "muscles" and "movements" is the existence of a hierarchy. The hierarchy hypothesis would predict that CM cell activity is muscle like and non-CM cell activity is movement like. In other words, direct input to motoneurons is in a language that does not need to be translated. The alternative is that a mixture of muscle-like and movement-like activity reaches the motoneuron and is used to create movements under different conditions. This project will determine which hypothesis is correct. We will also document, for the first time, the location and distribution of CM cells projecting to wrist muscle motoneurons. We will use the transneuronal transport of rabies virus to define the location of CM cells in the motor cortex that influence antagonist wrist muscles; flexor carpi radialis and extensor carpi radialis. If time permits, we will compare the distribution of CM cells in naive animals to those of animals trained to perform a skilled wrist task. This experiment will enable us to determine whether extensive training alters the cortical territory of CM cells in M1.