Garland S J, Gallina A, Pollock C L, Ivanova T D
Department of Physical Therapy, University of British Columbia , Vancouver, British Columbia , Canada.
Graduate Program in Rehabilitation Sciences, University of British Columbia , Vancouver, British Columbia , Canada.
J Neurophysiol. 2018 Jul 1;120(1):263-271. doi: 10.1152/jn.00555.2017. Epub 2018 Apr 4.
This study examined the task dependence of sensory inputs on motoneuron excitability by comparing the inhibitory postsynaptic potential (IPSP) evoked by stimulation of the sural nerve between a standing postural task (Free Standing) and a comparable voluntary isometric contraction performed in a supine position (Lying Supine). We hypothesized that there would be a smaller IPSP in standing than in the supine position, based on the task dependence of the ankle plantarflexor activity on the standing task. Ten healthy participants participated in a total of 15 experiments. Single motor unit (MU) firings were recorded with both intramuscular fine-wire electrodes and high-density surface electromyography. Participants maintained the MU discharge at 6-8 Hz in Free Standing or Lying Supine while the right sural nerve was stimulated at random intervals between 1 and 3 s. To evaluate the reflex response, the firing times of the discriminated MUs were used to construct peristimulus time histograms and peristimulus frequencygrams. The sural nerve stimulation resulted in weaker inhibition in Free Standing than in Lying Supine. This finding is discussed in relation to the putative activation of persistent inward currents in standing posture and the task-dependent advantages of overriding inhibitory synaptic inputs to the plantarflexors to maintain the standing posture. NEW & NOTEWORTHY The task-dependent modulation of sensory inputs on motoneuron excitability in standing is not well understood. Evoking an inhibitory postsynaptic potential (IPSP) resulted in a smaller IPSP in gastrocnemius motoneurons in standing than in the supine position. Mildly painful sensory inputs produced weaker motoneuron inhibition in standing, suggesting an imperative to maintain ankle plantarflexion activity for the task of upright stance.
本研究通过比较在站立姿势任务（自由站立）和仰卧位进行的类似自愿等长收缩（仰卧）中，刺激腓肠神经所诱发的抑制性突触后电位（IPSP），研究了感觉输入对运动神经元兴奋性的任务依赖性。基于踝跖屈肌活动对站立任务的依赖性，我们假设站立时的IPSP会比仰卧位时小。10名健康参与者共参与了15项实验。使用肌内细线电极和高密度表面肌电图记录单个运动单位（MU）的放电情况。参与者在自由站立或仰卧时将MU放电维持在6 - 8Hz，同时以1至3秒的随机间隔刺激右侧腓肠神经。为了评估反射反应，使用被区分的MU的放电时间来构建刺激时间直方图和刺激频率图。腓肠神经刺激在自由站立时产生的抑制作用比仰卧时弱。这一发现结合站立姿势中持续性内向电流的假定激活以及为维持站立姿势而优先抑制突触输入到跖屈肌的任务依赖性优势进行了讨论。新发现与值得注意之处站立时感觉输入对运动神经元兴奋性的任务依赖性调节尚不清楚。诱发抑制性突触后电位（IPSP）时，站立时腓肠肌运动神经元的IPSP比仰卧位时小。轻度疼痛的感觉输入在站立时产生的运动神经元抑制作用较弱，这表明为了维持直立姿势的任务，必须保持踝跖屈活动。
