Akay T, McVea D A, Tachibana A, Pearson K G
Department of Physiology, University of Alberta, Edmonton, Canada.
Exp Brain Res. 2006 Nov;175(2):211-22. doi: 10.1007/s00221-006-0542-3. Epub 2006 May 30.
To gain insight into the mechanism of coordination of stepping in the fore and hind legs of quadrupeds, we examined the kinematics of leg movements and the motor patterns in fore and hind leg flexor muscles in decerebrate walking cats when the two pairs of legs stepped on separate treadmills running at different speeds. When the front treadmill was slowed progressively from 0.6 to 0.3 m/s with the rear treadmill running at 0.6 m/s, the rate of stepping in both the fore and hind legs decreased and a 1:1 stepping ratio was maintained. The decrease in the rate of stepping in the hind legs was due primarily to an increase in the duration of the swing phase. Slowing the speed of the rear treadmill while keeping the front treadmill speed at 0.6 m/s decreased the rate of stepping of the hind legs, but had relatively little influence on the average rate of stepping in the forelegs. In this situation stepping in the fore and hind legs was uncoupled and the time of stepping in one hind leg relative to the ipsilateral foreleg progressively shifted during a walking sequence. Analysis of the timing of electromyographic (EMG) recordings from flexor muscles of the hip and elbow joints yielded insight into the neuronal mechanisms underlying the asymmetry in slowing either the front or rear treadmill. We propose that ipsilateral pattern generating networks are asymmetrically coupled via descending inhibitory pathways and an ascending excitatory pathway. We discuss how the characteristics of these linkages are functionally appropriate for establishing the normal timing of stepping in the hind and forelegs during slow walking.
为深入了解四足动物前腿和后腿协调迈步的机制，我们研究了去大脑的行走猫在两对腿分别在不同速度运行的跑步机上行走时腿部运动的运动学以及前腿和后腿屈肌的运动模式。当前面的跑步机从0.6米/秒逐渐减速到0.3米/秒，而后部跑步机以0.6米/秒的速度运行时，前腿和后腿的迈步频率均降低，且保持1:1的迈步比例。后腿迈步频率的降低主要是由于摆动期持续时间的增加。在保持前面跑步机速度为0.6米/秒的同时减慢后部跑步机的速度，会降低后腿的迈步频率，但对前腿的平均迈步频率影响相对较小。在这种情况下，前腿和后腿的迈步不再耦合，在行走过程中，一条后腿相对于同侧前腿的迈步时间会逐渐发生变化。对髋关节和肘关节屈肌的肌电图（EMG）记录时间进行分析，有助于深入了解减慢前部或后部跑步机速度时不对称现象背后的神经元机制。我们提出同侧模式生成网络通过下行抑制通路和上行兴奋通路不对称耦合。我们讨论了这些连接的特征在功能上如何适合于在慢走过程中建立后腿和前腿正常的迈步时间。
