Johansson R S, Hger C, Bäckström L
Department of Physiology, Umeå University, Sweden.
Exp Brain Res. 1992;89(1):204-13. doi: 10.1007/BF00229017.
During manipulation involving restraint of 'active' (mechanically unpredictable) objects, it is presumed that the control of the grip and other reaction forces more regularly relies on somatosensory input than during manipulation of 'passive' (mechanically predictable) objects. In companion studies we have shown that grip forces are automatically adjusted to the amplitude and the rate of distal pulling loads imposed through an 'active' object held in a precision grip. In this study anesthesia of either one or both digits holding the manipulandum was used to examine whether the grip force regulation was dependent on afferent signals from the digits. Five types of trapezoidal load force profiles of various rate and amplitude combinations were given in an unpredictable sequence while the subject was prevented from seeing the hand. Grip forces, load forces and position of the manipulandum in the pulling direction were recorded. With both digits anesthetized the load amplitude changes yielded considerably less grip force modulation and in many trials obvious grip force responses were absent. Moreover, the latencies between the onset of the load changes and the observed grip force responses were much prolonged. However, there was pronounced inter-individual variation. Subjects exhibiting a lower stiffness in the pulling direction, probably due to more flexed fingers when holding the manipulandum, showed a higher force modulation, higher responsiveness to the load ramps and shorter latencies. Hence, under certain conditions afferent input from receptors proximal to the digits could be utilized to provide some grip regulation. The evoked grip force responses showed an initial response similar to the normally occurring 'catch-up' response, but it was not graded by the load force rate. Also, there was no 'tracking' response, suggesting that the latter was contingent upon a moment-to-moment control using afferent input from the digits. With only one digit anesthetized (thumb) the handicap was less severe. Thus, the grip force regulation was impaired under any condition of digital anesthesia, i.e., afferent input from both index finger and thumb was required for the adequate operation of the grip force regulation.
在涉及对“主动”（机械上不可预测）物体进行约束的操作过程中，与对“被动”（机械上可预测）物体的操作相比，握持和其他反作用力的控制被认为更经常依赖于体感输入。在相关研究中，我们已经表明，握持力会自动根据通过精确握持的“主动”物体施加的远端拉力载荷的幅度和速率进行调整。在本研究中，使用对握持操作对象的一个或两个手指进行麻醉的方法，来检查握持力调节是否依赖于来自手指的传入信号。在不让受试者看到手的情况下，以不可预测的顺序给出五种不同速率和幅度组合的梯形加载力曲线。记录握持力、加载力以及操作对象在拉伸方向上的位置。当两个手指都被麻醉时，加载幅度变化引起的握持力调制明显减少，并且在许多试验中没有明显的握持力响应。此外，加载变化开始与观察到的握持力响应之间的延迟大大延长。然而，个体间存在明显差异。在拉伸方向上表现出较低刚度的受试者，可能是因为握持操作对象时手指更弯曲，他们表现出更高的力调制、对加载斜坡的更高响应性以及更短的延迟。因此，在某些条件下，可以利用来自手指近端感受器的传入输入来提供一些握持调节。诱发的握持力响应显示出与正常发生的“追赶”响应相似的初始响应，但它不是由加载力速率分级的。而且，没有“跟踪”响应，这表明后者取决于使用来自手指的传入输入进行的即时控制。当只麻醉一个手指（拇指）时，障碍不太严重。因此，在任何手指麻醉的情况下，握持力调节都会受损，即食指和拇指的传入输入对于握持力调节的正常运作都是必需的。
