Martin J H, Cooper S E, Ghez C
Center for Neurobiology and Behavior, College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA.
Exp Brain Res. 1995;102(3):379-92. doi: 10.1007/BF00230643.
The present study examines the kinematic features of forelimb movements made by cats reaching for food in horizontal target wells located at different heights and distances. Wrist paths consisted of two relatively straight segments joined at a "via-point" in front of the aperture of the food well. In the initial lift phase, the paw was raised to the via-point in front of the target. In the second, or thrust phase, the paw was directed forward into the food well. During the lift, the paw was moved toward the target primarily by elbow flexion, accompanied by a sequence of biphasic shoulder and wrist movements. Thrust was accomplished primarily by shoulder flexion while the wrist and the paw were maintained at near-constant angles. The animals varied the height of the reach primarily by varying elbow flexion with proportional changes in elbow angular velocity and angular acceleration and with corresponding variations in wrist speed. Thus, cats reached for targets at different heights by scaling a common kinematic profile. Over a relatively large range of target heights, animals maintained movement duration constant, according to a simple "pulse-height" control strategy (isochronous scaling). For reaches to a given target height, animals compensated for variability in peak acceleration by variations in movement time. We examined the coordination between the shoulder and the wrist with the elbow. Early during the lift, peak shoulder extensor and peak elbow flexor accelerations were synchronized. Late during the lift phase, wrist extensor acceleration was found to occur during the period of elbow flexor deceleration. We hypothesize that these linkages could, in part, be due to passive mechanical interactions. To determine how the angular trajectories of the different joints were organized in relation to target location, we plotted joint kinematic changes directly on the wrist and MCP joint paths. These plots revealed that for all target heights and movement speeds, wrist extensor deceleration occurred at approximately the same spatial location with respect to the target. This analysis also demonstrated that the second phase of MCP flexion occurred when the paw was below the lower lip of the food well, while the subsequent extension occurred after the tip cleared this obstacle. During thrust, wrist and MCP angles were maintained, reflecting the need to align the paw within the food well. Our findings suggest that cats plan the reaching phase of prehension as a sequence of discrete movement segments, each serving a particular goal in the task, rather than as an single unit.
本研究考察了猫在水平目标孔中抓取位于不同高度和距离的食物时前肢运动的运动学特征。腕部路径由在食物孔开口前方的一个“过渡点”处相连的两个相对较直的部分组成。在初始抬起阶段，爪子被抬到目标前方的过渡点。在第二个阶段，即推阶段，爪子向前伸进食物孔。在抬起过程中，爪子主要通过肘部弯曲朝向目标移动，同时伴随着一系列双相的肩部和腕部运动。推主要通过肩部弯曲完成，而腕部和爪子保持在接近恒定的角度。动物主要通过改变肘部弯曲程度、肘部角速度和角加速度的比例变化以及腕部速度的相应变化来改变抓取的高度。因此，猫通过调整共同的运动学轮廓来抓取不同高度的目标。在相对较大的目标高度范围内，动物根据简单的“脉冲高度”控制策略（等时缩放）保持运动持续时间恒定。对于到达给定目标高度的抓取动作，动物通过改变运动时间来补偿峰值加速度的变化。我们研究了肩部、腕部与肘部之间协调关系。在抬起早期，肩部伸肌峰值加速度和肘部屈肌峰值加速度同步。在抬起阶段后期，发现腕部伸肌加速度出现在肘部屈肌减速期间。我们推测这些联系部分可能是由于被动机械相互作用。为了确定不同关节的角轨迹相对于目标位置是如何组织的，我们将关节运动学变化直接绘制在腕部和掌指关节路径上。这些图显示，对于所有目标高度和运动速度，腕部伸肌减速相对于目标发生在大致相同的空间位置。该分析还表明，掌指关节弯曲的第二阶段发生在爪子低于食物孔下唇时，而随后的伸展发生在爪子尖端越过这个障碍物之后。在推阶段，腕部和掌指关节角度保持不变，这反映了需要将爪子对准食物孔内部。我们的研究结果表明，猫将抓握的伸展阶段规划为一系列离散的运动片段，每个片段在任务中服务于一个特定目标，而不是作为一个单一单元。
