This study assessed whether changes in size or time- course of excitatory po stsynaptic potentials (EPSPs) in motoneurons innervating spastic muscle could in duce a greater synaptic response, and thereby contribute to...This study assessed whether changes in size or time- course of excitatory po stsynaptic potentials (EPSPs) in motoneurons innervating spastic muscle could in duce a greater synaptic response, and thereby contribute to reflex hyperexcitabi lity. We compared motor unit (MU) firing patterns elicited by tendon taps applie d to both spastic and contralateral (nonspastic) biceps brachii muscle in hemipa retic stroke subjects. Based on recordings of 115 MUs, significantly shortened E PSP rise times were present on the spastic side, but with no significant differe nces in estimated EPSP amplitude. These changes may contribute to hyperexcitable reflex responses at short latency, but the EPSP amplitude changes appear insuff icient to account for global differences in reflex excitability.展开更多
提高蛇形机器人的三维运动控制能力是提高蛇形机器人环境适应能力的关键之一.虽然联结中枢模式生成器(Connectionist central pattern generator,CCPG)模型具有复杂度小、适合硬件实现等优点,但是目前的CCPG模型难以生成相位协调的多自...提高蛇形机器人的三维运动控制能力是提高蛇形机器人环境适应能力的关键之一.虽然联结中枢模式生成器(Connectionist central pattern generator,CCPG)模型具有复杂度小、适合硬件实现等优点,但是目前的CCPG模型难以生成相位协调的多自由度运动的控制信号,从而限制了它的三维步态控制能力.本文根据生物CPG机制的分层结构和运动神经元的功能,提出一个有层次化结构的CCPG(Hierarchical CCPG,HCCPG)模型.HCCPG模型由基本节律信号生成层、模式形成层、运动信号调整层这三个部分组成.运动信号调整层的运动神经元能够独立地对模式形成层的输出信号的幅值、相位等进行调整,从而较好地解决了CCPG模型难以生成相位协调的多自由度运动控制信号的问题.HCCPG模型具有步态控制能力强、复杂度小、有良好的扩展性等优点,从而适合用于控制三维步态.在HCCPG模型的基础上提出一个三维步态控制方法.仿真验证了这个控制方法的有效性.展开更多
Objective: Previous reports from our laboratory have described short-latency contractions in muscles of the distal upper limb following stimulation of lower limb nerves or skin in persons with injury to the cervical s...Objective: Previous reports from our laboratory have described short-latency contractions in muscles of the distal upper limb following stimulation of lower limb nerves or skin in persons with injury to the cervical spinal cord. It takes 6 or more months for interlimb reflexes (ILR) to appear following acute spinal cord injury (SCI), suggesting they might be due to new synaptic interconnections between lower limb sensory afferents and motoneurons in the cervical enlargemen t. In this study, we asked if once formed, the strength of these synaptic connec tions increased over time, a finding that would be consistent with the above hyp othesis. Methods: We studied persons with sub-acute and/or chronic cervical SCI . ILR were elicited by brief trains of electrical pulses applied to the skin ove rlying the tibial nerve atthe back of the knee. Responses were quantified based on their presence or absence in different upper limb muscles. We also generated peri-stimulus time histograms for single motor unitresponse latency, probabilit y, and peak duration. Comparisons of these parameters were made in subjects at s ub-acute versus chronic stages post-injury. Results: In persons with sub-acut e SCI, the probability of seeing ILR in a given muscle of the forearm or hand wa s low at first, but increased substantially over the next 1-2 years. Motor unit responses at this sub-acute stage had a prolonged and variable latency, with a lower absolute response probability, compared to findings from subjects with ch ronic (i.e. stable) SCI. Conclusions: Our findings demonstrate that interlimb re flex activity, once established after SCI,shows signs of strengthening synaptic contacts between afferentand efferent components, consistent with ongoing synapt ic plasticity. Significance: Neurons within the adult human spinal cord caudal t o a lesion site are not static, but appear to be capable of developing novel-ye t highly efficacious-synaptic contacts following trauma-induced partial denerv ation. In this case, such contacts between ascending afferents and cervical moto neurons do not appear to provide any functional benefit to the subject. In fact their presence may limit the regenerative effort of supraspinal pathways which o riginally innervated these motoneurons, should effort in animal models to promot e regeneration across the lesion epicenter be successfully translated to humans with chronic SCI.展开更多
文摘This study assessed whether changes in size or time- course of excitatory po stsynaptic potentials (EPSPs) in motoneurons innervating spastic muscle could in duce a greater synaptic response, and thereby contribute to reflex hyperexcitabi lity. We compared motor unit (MU) firing patterns elicited by tendon taps applie d to both spastic and contralateral (nonspastic) biceps brachii muscle in hemipa retic stroke subjects. Based on recordings of 115 MUs, significantly shortened E PSP rise times were present on the spastic side, but with no significant differe nces in estimated EPSP amplitude. These changes may contribute to hyperexcitable reflex responses at short latency, but the EPSP amplitude changes appear insuff icient to account for global differences in reflex excitability.
文摘提高蛇形机器人的三维运动控制能力是提高蛇形机器人环境适应能力的关键之一.虽然联结中枢模式生成器(Connectionist central pattern generator,CCPG)模型具有复杂度小、适合硬件实现等优点,但是目前的CCPG模型难以生成相位协调的多自由度运动的控制信号,从而限制了它的三维步态控制能力.本文根据生物CPG机制的分层结构和运动神经元的功能,提出一个有层次化结构的CCPG(Hierarchical CCPG,HCCPG)模型.HCCPG模型由基本节律信号生成层、模式形成层、运动信号调整层这三个部分组成.运动信号调整层的运动神经元能够独立地对模式形成层的输出信号的幅值、相位等进行调整,从而较好地解决了CCPG模型难以生成相位协调的多自由度运动控制信号的问题.HCCPG模型具有步态控制能力强、复杂度小、有良好的扩展性等优点,从而适合用于控制三维步态.在HCCPG模型的基础上提出一个三维步态控制方法.仿真验证了这个控制方法的有效性.
文摘Objective: Previous reports from our laboratory have described short-latency contractions in muscles of the distal upper limb following stimulation of lower limb nerves or skin in persons with injury to the cervical spinal cord. It takes 6 or more months for interlimb reflexes (ILR) to appear following acute spinal cord injury (SCI), suggesting they might be due to new synaptic interconnections between lower limb sensory afferents and motoneurons in the cervical enlargemen t. In this study, we asked if once formed, the strength of these synaptic connec tions increased over time, a finding that would be consistent with the above hyp othesis. Methods: We studied persons with sub-acute and/or chronic cervical SCI . ILR were elicited by brief trains of electrical pulses applied to the skin ove rlying the tibial nerve atthe back of the knee. Responses were quantified based on their presence or absence in different upper limb muscles. We also generated peri-stimulus time histograms for single motor unitresponse latency, probabilit y, and peak duration. Comparisons of these parameters were made in subjects at s ub-acute versus chronic stages post-injury. Results: In persons with sub-acut e SCI, the probability of seeing ILR in a given muscle of the forearm or hand wa s low at first, but increased substantially over the next 1-2 years. Motor unit responses at this sub-acute stage had a prolonged and variable latency, with a lower absolute response probability, compared to findings from subjects with ch ronic (i.e. stable) SCI. Conclusions: Our findings demonstrate that interlimb re flex activity, once established after SCI,shows signs of strengthening synaptic contacts between afferentand efferent components, consistent with ongoing synapt ic plasticity. Significance: Neurons within the adult human spinal cord caudal t o a lesion site are not static, but appear to be capable of developing novel-ye t highly efficacious-synaptic contacts following trauma-induced partial denerv ation. In this case, such contacts between ascending afferents and cervical moto neurons do not appear to provide any functional benefit to the subject. In fact their presence may limit the regenerative effort of supraspinal pathways which o riginally innervated these motoneurons, should effort in animal models to promot e regeneration across the lesion epicenter be successfully translated to humans with chronic SCI.
