Neural mechanisms underlying the adaptive plasticity of human locomotion

本工作的目的是为了更好地了解人类运动神经控制的适应能力/学习能力。在拟议的实验中，运动控制将受到挑战，让受试者在跑步机上行走，改变由定制的机器人矫形器产生的力环境(“力场”)。为了在力场存在的情况下正常行走，参与者需要暂时修改他们刻板的肌肉激活模式，这是一种运动学习的实验模型。在接下来的五年里，将解决以下三个目标：*OBJ#1：确定伸展和负荷输入对运动适应的贡献。*当在力场中行走时，受试者通过来自肌梭(肌肉长度/速度)、高尔基肌腱器官(GTO；肌肉负荷)和足部皮肤感受器(压力分布)的感觉反馈，获得关于他们运动错误的信息。我们最近的研究表明，皮肤受体有助于适应。在本提案中，我们将重点介绍主轴和GTO的贡献。我们将在运动适应过程中使用振动(纺锤)或电刺激肌肉(GTOS)来选择性地“扰乱”选定的输入(感觉弹幕)。我们的假设是，在感觉弹幕过程中观察到的适应缺陷将提供关于这种输入对运动适应的作用的信息。*OBJ#2：测试肌肉激活模式对复杂力场的适应能力的程度。据推测，由于自动运动网络对运动生成的重要贡献，步态过程中的适应性可塑性可能是有限的。在这里，我们将使用我们的RAFO来产生步态中脚踝运动的分级扰动。通过从抵抗到增加辅助量，将有可能增加学习的难度，从简单的肌肉激活幅度的变化变成类似于拮抗肌腱转移的激活的“相反转”。我们的假设是，参与者将能够适应需要改变肌肉激活幅度的情况，但不能进行相位逆转。*OBJ#3：更好地了解中枢疲劳如何影响运动学习的习得/保持。*在运动学习过程中经常会出现肌肉疲劳。它是如何干扰学习的在很大程度上仍是个未知数。在这里，我们将测试皮质脊髓兴奋性，脚踝本体感觉和短期疲劳运动后步态的运动适应/保持。我们的假设是，疲劳对运动适应的影响很小，但对保持能力的有害影响更大。*影响。通过有条不紊地研究人类在几种互补适应情况下的行走，这项研究计划将在运动可塑性背后的神经机制方面取得重要发现。

The aim of the present work is to better understand the adaptive capacity/learning ability of the neural control of human locomotion. In the proposed experiments, locomotor control will be challenged by having subjects walk on a treadmill in altered force environments (“force fields”) generated by a custom-made robotized orthosis. In order to walk normally in the presence of the force field, participants need to temporarily modify their stereotypic muscle activation pattern, an experimental model of motor learning. Over the next five years, the following 3 objectives will be addressed:***OBJ#1: Define the contribution of stretch and load inputs to locomotor adaptation.***When walking in a force field, subjects obtain information about their movement errors through sensory feedback from muscle spindles (muscle length/velocity), Golgi tendon organs (GTOs; muscle loading), and foot cutaneous receptors (pressure distribution). We have recently shown that cutaneous receptors contribute to adaptation. In this proposal, we will focus on spindle and GTO contributions. We will use vibration (spindle) or electrical stimulation of the muscle (GTOs) during locomotor adaptation to selectively “scramble” the selected input (sensory barrage). Our hypothesis is that deficits in adaptation observed during sensory barrage will provide information on the role of this input for locomotor adaptation.***OBJ#2: Test the extent of adaptive capacity of the muscle activation pattern to complex force fields. ***It has been hypothesized that adaptive plasticity during gait might be limited due to the important contribution of automatic locomotor networks to movement generation. Here we will use our rAFO to produce graded perturbations to ankle movement during gait. By going from resistance to increasing amounts of assistance, it will be possible to increase the level of difficulty of the learning, going from simple changes in muscle activation amplitude to a "phase-reversal" of activation, akin to antagonist tendon-transfer. Our hypothesis is that participants will be able to adapt to situations requiring changes in muscle activation amplitude, but incapable of phase reversal. ***OBJ#3: Better understand how central fatigue affects acquisition/retention of locomotor learning. ***Muscle fatigue is often present during motor learning. How it interferes with learning remains largely unknown. Here, we will test corticospinal excitability, ankle proprioception and locomotor adaptation/retention during gait after a short-duration fatiguing exercise. Our hypothesis is that fatigue will have a minimal effect on locomotor adaptation but a larger deleterious effect on retention. ***IMPACT. By methodically studying human walking under several complementary adaptive situations, this research program will make important discoveries about neural mechanisms underlying locomotor plasticity.