Ashe J
Brain Sciences Center (11B), VAMC, Minneapolis, MN 55417, USA.
Behav Brain Res. 1997 Jun;86(1):1-15. doi: 10.1016/s0166-4328(96)00145-3.
The relation between the activity of cells in the motor cortex and static force has been studied extensively. Most studies have concentrated on the relation to the magnitude of force; this relation is more or less monotonic. The slope of the relation, however, shows considerable variation among different studies and seems to be inversely associated with the range of forces over which the cell activity has been studied. Cells in the motor cortex also show variation in activity with the direction of static force. When both the direction and the magnitude of static force are allowed to vary, a majority of cells show significant changes in activity with direction of force alone, an intermediate number relate to both direction and magnitude, while a small number relate purely to the magnitude. This suggests that the direction of static force can be controlled independently of its magnitude and that this directional signal is especially prominent in the motor cortex. In general, it has been more difficult to study the relations to dynamic force. There is a correlation between motor cortex cell activity and the rate of change of force. The direction of dynamic force is also an important determinant of cell activity. When both static and dynamic force output are required (for example, with arm movement in the presence of gravity) it is the dynamic signal that is most clearly reflected in motor cortex activity. The relations between motor cortex activity and static or dynamic force are not invariant, but may be modified by the behavioral context of the motor output.
运动皮层中细胞活动与静力之间的关系已得到广泛研究。大多数研究集中在与力的大小的关系上；这种关系或多或少是单调的。然而，不同研究中这种关系的斜率显示出相当大的差异，并且似乎与研究细胞活动的力的范围呈负相关。运动皮层中的细胞活动也随静力方向而变化。当静力的方向和大小都允许变化时，大多数细胞仅随力的方向显示出显著的活动变化，中等数量的细胞与方向和大小都有关，而少数细胞仅与大小有关。这表明静力的方向可以独立于其大小进行控制，并且这种方向信号在运动皮层中尤为突出。一般来说，研究与动力的关系更加困难。运动皮层细胞活动与力的变化率之间存在相关性。动力的方向也是细胞活动的一个重要决定因素。当需要静力和动力输出时（例如，在有重力的情况下手臂运动），动力信号在运动皮层活动中最清晰地体现出来。运动皮层活动与静力或动力之间的关系并非一成不变，而是可能会受到运动输出行为背景的影响。
