Lacquaniti F, Ivanenko Y P, Zago M
Human Physiology Section, University of Rome Tor Vergata, Scientific Institute Santa Lucia, Via Ardeatina 306, 00179 Rome, Italy.
Arch Ital Biol. 2002 Oct;140(4):263-72.
The planar law of inter-segmental co-ordination we described may emerge from the coupling of neural oscillators between each other and with limb mechanical oscillators. Muscle contraction intervenes at variable times to re-excite the intrinsic oscillations of the system when energy is lost. The hypothesis that a law of coordinative control results from a minimal active tuning of the passive inertial and viscoelastic coupling among limb segments is congruent with the idea that movement has evolved according to minimum energy criteria (1, 8). It is known that multi-segment motion of mammals locomotion is controlled by a network of coupled oscillators (CPGs, see 18, 33, 37). Flexible combination of unit oscillators gives rise to different forms of locomotion. Inter-oscillator coupling can be modified by changing the synaptic strength (or polarity) of the relative spinal connections. As a result, unit oscillators can be coupled in phase, out of phase, or with a variable phase, giving rise to different behaviors, such as speed increments or reversal of gait direction (from forward to backward). Supra-spinal centers may drive or modulate functional sets of coordinating interneurons to generate different walking modes (or gaits). Although it is often assumed that CPGs control patterns of muscle activity, an equally plausible hypothesis is that they control patterns of limb segment motion instead (22). According to this kinematic view, each unit oscillator would directly control a limb segment, alternately generating forward and backward oscillations of the segment. Inter-segmental coordination would be achieved by coupling unit oscillators with a variable phase. Inter-segmental kinematic phase plays the role of global control variable previously postulated for the network of central oscillators. In fact, inter-segmental phase shifts systematically with increasing speed both in man (4) and cat (38). Because this phase-shift is correlated with the net mechanical power output over a gait cycle (3, 4), phase control could be used for limiting the overall energy expenditure with increasing speed (22). Adaptation to different walking conditions, such as changes in body posture, body weight unloading and backward walk, also involves inter-segmental phase tuning, as does the maturation of limb kinematics in toddlers.
我们所描述的节段间协调的平面定律，可能源自神经振荡器之间以及与肢体机械振荡器之间的耦合。当能量损失时，肌肉收缩会在不同时间介入，以重新激发系统的固有振荡。协调控制定律源于肢体节段间被动惯性和粘弹性耦合的最小主动调谐这一假设，与运动根据最小能量标准进化的观点是一致的(1, 8)。众所周知，哺乳动物运动的多节段运动由耦合振荡器网络(中枢模式发生器，见18, 33, 37)控制。单位振荡器的灵活组合产生了不同形式的运动。振荡器间的耦合可以通过改变相对脊髓连接的突触强度(或极性)来改变。结果，单位振荡器可以同相、异相或具有可变相位地耦合，从而产生不同的行为，如速度增加或步态方向反转(从前向后)。脊髓上中枢可能驱动或调节协调中间神经元的功能组，以产生不同的行走模式(或步态)。虽然人们通常认为中枢模式发生器控制肌肉活动模式，但一个同样合理的假设是，它们反而控制肢体节段运动模式(22)。根据这种运动学观点，每个单位振荡器将直接控制一个肢体节段，交替产生该节段的向前和向后振荡。节段间的协调将通过以可变相位耦合单位振荡器来实现。节段间运动相位起着先前为中枢振荡器网络假设的全局控制变量的作用。事实上，在人类(4)和猫(38)中，节段间相位都随着速度的增加而系统地变化。因为这种相位变化与一个步态周期内的净机械功率输出相关(3, 4)，相位控制可用于随着速度增加而限制整体能量消耗(22)。适应不同的行走条件，如身体姿势的变化、身体重量卸载和向后行走，也涉及节段间相位调整，幼儿肢体运动学的成熟也是如此。
