Neural mechanisms underlying the adaptive plasticity of human locomotion

本工作的目的是更好地了解人类运动的神经控制的自适应能力/学习能力。在拟议的实验中，运动控制将受到挑战，让受试者在由定制的机器人矫形器产生的改变的力环境（“力场”）中在跑步机上行走。为了在力场的存在下正常行走，参与者需要暂时改变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3个目标：* 目标1：定义拉伸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）、高尔基体腱器官（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其运动错误的信息。我们最近发现，皮肤受体有助于适应。在本提案中，我们将侧重于主轴和GTO的贡献。我们将在运动适应过程中使用振动（纺锤体）或肌肉电刺激（GTO）来选择性地“扰乱”所选输入（感觉障碍）。我们的假设是，在感觉障碍期间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。目标2：测试肌肉激活模式对复杂力场的适应能力。* 有人假设，由于自动运动网络对运动生成的重要贡献，步态期间的适应性可塑性可能受到限制。在这里，我们将使用我们的rAFO在步态期间对踝关节运动产生分级扰动。通过从阻力到增加辅助量，将有可能增加学习的难度水平，从肌肉激活幅度的简单变化到激活的“相位逆转”，类似于拮抗剂肌腱转移。我们的假设是，参与者将能够适应需要肌肉激活幅度变化的情况，但不能进行相位逆转。 * 目标3：更好地理解中枢疲劳如何影响运动学习的获得/保持。 * 肌肉疲劳经常出现在运动学习过程中。它是如何干扰学习的，在很大程度上还不清楚。在这里，我们将测试皮质脊髓兴奋性，踝关节本体感觉和运动适应/保持在步态后，短时间疲劳运动。我们的假设是，疲劳将有一个运动适应的影响最小，但保留较大的有害影响。 * 影响。通过系统地研究人类在几种互补适应情况下的行走，该研究计划将对运动可塑性的神经机制做出重要发现。

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.