Hendrix Claudia M, Mason Carolyn R, Ebner Timothy J
Department of Neuroscience, University of Minnesota, Lions Research Bldg., Rm. 421, 2001 Sixth St. SE, Minneapolis, MN 55455, USA.
J Neurophysiol. 2009 Jul;102(1):132-45. doi: 10.1152/jn.00016.2009. Epub 2009 Apr 29.
A fundamental question is how the CNS controls the hand with its many degrees of freedom. Several motor cortical areas, including the dorsal premotor cortex (PMd) and primary motor cortex (M1), are involved in reach to grasp. Although neurons in PMd are known to modulate in relation to the type of grasp and neurons in M1 in relation to grasp force and finger movements, whether specific parameters of whole hand shaping are encoded in the discharge of these cells has not been studied. In this study, two monkeys were trained to reach and grasp 16 objects varying in shape, size, and orientation. Grasp force was explicitly controlled, requiring the monkeys to exert either three or five levels of grasp force on each object. The animals were unable to see the objects or their hands. Single PMd and M1 neurons were recorded during the task, and cell firing was examined for modulation with object properties and grasp force. The firing of the vast majority of PMd and M1 neurons varied significantly as a function of the object presented as well as the object grasp dimension. Grasp dimension of the object was an important determinant of the firing of cells in both PMd and M1. A smaller percentage of PMd and M1 neurons were modulated by grasp force. Linear encoding was prominent with grasp force but less so with grasp dimension. The correlations with grasp dimension and grasp force were stronger in the firing of M1 than PMd neurons and across both regions the modulation with these parameters increased as reach to grasp proceeded. All PMd and M1 neurons that signaled grasp force also signaled grasp dimension, yet the two signals showed limited interactions, providing a neural substrate for the independent control of these two parameters at the behavioral level.
一个基本问题是中枢神经系统如何控制具有多个自由度的手部。包括背侧运动前区皮质（PMd）和初级运动皮质（M1）在内的几个运动皮质区域参与了伸手抓握动作。虽然已知PMd中的神经元会根据抓握类型进行调节，M1中的神经元会根据抓握力和手指运动进行调节，但这些细胞的放电是否编码了整个手部塑形的特定参数尚未得到研究。在本研究中，训练了两只猴子去伸手抓握16个形状、大小和方向各异的物体。明确控制抓握力，要求猴子对每个物体施加三种或五种抓握力水平。动物无法看到物体或它们的手。在任务过程中记录单个PMd和M1神经元，并检查细胞放电是否随物体属性和抓握力而调节。绝大多数PMd和M1神经元的放电随所呈现的物体以及物体抓握维度而显著变化。物体的抓握维度是PMd和M1中细胞放电的一个重要决定因素。受抓握力调节的PMd和M1神经元比例较小。抓握力的线性编码很突出，但抓握维度的线性编码则较弱。M1神经元放电与抓握维度和抓握力的相关性比PMd神经元更强，并且在两个区域中，随着伸手抓握动作的进行，这些参数的调节作用增强。所有发出抓握力信号的PMd和M1神经元也发出抓握维度信号，但这两个信号之间的相互作用有限，为这两个参数在行为水平上的独立控制提供了神经基础。
