Primary motor cortical neurons encode functional muscle synergies
Primary motor cortical neurons encode functional muscle synergies
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DOI：
10.1007/s00221-002-1166-x
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发表时间：
2002-09-01
影响因子：
2
通讯作者：
Miller, LE
中科院分区：
文献类型：
--
作者：
Holdefer, RN;Miller, LE
许多不同的运动学和运动学信号被认为是初级运动皮质控制下的可能变量。尽管存在对运动神经元的直接投射，但肌肉激活作为一种受控变量，受到的关注较少。此外，尽管众所周知，下行纤维投射到多个运动池，但以前还没有关于神经元调制和肌肉群活动之间关系的客观、定量的研究报道。我们记录了位于两只猴子初级运动皮质的310个神经元的放电，以及各种手臂和手部肌肉的活动。当猴子伸手按下一系列发光的按钮时，数据被记录下来。通过计算给定神经元的放电率与每个校正、过滤的肌电之间的线性互相关来确定给定神经元相对于每块肌肉的放电的相似性。然后构建了一个“功能链接向量”，它表达了该神经元的放电与整个肌肉集的相似性。我们在两只猴子的高阶肌肉间隙中发现了离散的功能链接向量组，这与用其他方法测量的神经元的功能特性相对应。其中几组似乎代表了肌肉的功能协同，例如伸展肢体、按下按钮或张开手为按压做准备所需的肌肉。当通过主成分分析降低该空间的维度时，最初识别的神经元簇保持良好的分离。这些结果与初级运动皮质中单个神经元的放电编码相对较少的功能相关肌肉组的活动的假设一致。重要的是要确定这些结果是否也适用于更复杂的行为，以及这些功能肌肉协同表示在多大程度上保持固定的行为。
Many different kinematic and kinetic signals have been proposed as possible variables under the control of the primary motor cortex. Despite the presence of direct projections to motor neurons, muscle activation has received less attention as a controlled variable. Furthermore, although it is well known that descending fibers project to multiple motor pools, an objective, quantitative study of the relation between neuronal modulation and the activity of groups of muscles has not previously been reported. We have recorded the discharge of 310 neurons located in the primary motor cortex of two monkeys, along with the activity of a variety of arm and hand muscles. Data were recorded while the monkey reached to and pressed a series of illuminated buttons. The similarity of a given neuron's discharge with respect to each muscle was determined by calculating the linear cross-correlation between its discharge rate and each rectified, filtered electromyogram. A "functional linkage vector" was then constructed, which expressed the similarity of that neuron's discharge to the entire set of muscles. We discovered discrete groups of functional linkage vectors within the high order muscle space for both monkeys which corresponded to functional properties of the neurons measured by other methods. Several of these groups appeared to represent a functional synergy of muscles, such as those required to extend the limb, press a button, or open the hand in preparation for the press. When the dimensionality of this space was reduced by a principal components analysis, the originally identified clusters of neurons remained well separated. These results are consistent with the hypothesis that the discharge of individual neurons in the primary motor cortex encodes the activity of a relatively small number of functionally relevant groups of muscles. It will be important to determine whether these results will also apply to more complex behavior, and to what extent these functional muscle synergy representations remain fixed across behaviors.