Loeb E P, Giszter S F, Borghesani P, Bizzi E
Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge 02139.
Somatosens Mot Res. 1993;10(1):81-95. doi: 10.3109/08990229309028826.
Spinalized frogs were microstimulated in the intermediate grey layers of the lumbar spinal cord; the forces evoked in the hindlimb were measured at several limb positions. The data were expressed as force fields. After the collection of many force fields, the dorsal roots were cut with the stimulating electrode in place, and the position-dependent stimulation-evoked forces were again measured repeatedly. We found that the position-dependent pattern of evoked forces--the force fields--did not change after the dorsal roots were cut. In other words, the postcut evoked forces pointed in the same direction as the precut evoked forces. This result was predicted and confirmed by the muscle activations (EMGs): Before and after the dorsal roots were cut, the same muscles were activated in the same proportions. In all limb positions, the rank ordering of the muscle activations remained fixed. The stimulation needed to evoke forces was increased by deafferentation, and there were subtle changes in the force magnitudes that were consistent with a linearization of the muscle stiffness by the afferents. We conclude that the microstimulation activated specific muscle synergies that resulted in limb forces pointing toward a particular posture. The patterns of evoked forces were predominantly attributable to feedforward activation of these muscle synergies.
对脊髓横断的青蛙的腰段脊髓中间灰质层进行微刺激；在几个肢体位置测量后肢产生的力。数据以力场表示。收集多个力场后，在刺激电极就位的情况下切断背根，并再次反复测量与位置相关的刺激诱发力。我们发现，切断背根后，诱发力的位置依赖性模式——力场——并未改变。换句话说，切断背根后诱发的力与切断前诱发的力指向相同方向。这一结果通过肌肉激活（肌电图）得到了预测和证实：切断背根前后，相同的肌肉以相同的比例被激活。在所有肢体位置，肌肉激活的排序保持不变。去传入神经后，诱发力所需的刺激增加，并且力的大小存在细微变化，这与传入神经使肌肉刚度线性化一致。我们得出结论，微刺激激活了特定的肌肉协同作用，导致肢体力指向特定姿势。诱发力的模式主要归因于这些肌肉协同作用的前馈激活。
