School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada.
Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada.
J Physiol. 2021 Jul;599(14):3611-3625. doi: 10.1113/JP281744. Epub 2021 Jun 21.
We examined the influence of cutaneous feedback from the heel and metatarsal regions of the foot sole on the soleus stretch reflex pathway during standing. We found that heel electrical stimuli suppressed and metatarsal stimuli enhanced the soleus vibration response. Follow-up experiments indicated that the interaction between foot sole cutaneous feedback and the soleus vibration response was likely not mediated by presynaptic inhibition and was contingent upon a modulation at the ⍺-motoneuron pool level. The spatially organized interaction between cutaneous feedback from the foot sole and the soleus vibration response provides information about how somatosensory information is combined to appropriately respond to perturbations during standing.
Cutaneous feedback from the foot sole provides balance-relevant information and has the potential to interact with spinal reflex pathways. In this study, we examined how cutaneous feedback from the foot sole (heel and metatarsals) influenced the soleus response to proprioceptive stimuli during standing. We delivered noisy vibration (10-115 Hz) to the right Achilles tendon while we intermittently applied electrical pulse trains (five 1-ms pulses at 200 Hz, every 0.8-1.0 s) to the skin under either the heel or the metatarsals of the ipsilateral foot sole. We analysed time-dependent (referenced to cutaneous stimuli) coherence and cross-correlations between the vibration acceleration and rectified soleus EMG. Vibration-EMG coherence was observed across a bandwidth of ∼10-80 Hz, and coherence was suppressed by heel but enhanced by metatarsal cutaneous stimuli. Cross-correlations showed soleus EMG was correlated with the vibration (∼40 ms lag) and cross-correlations were also suppressed by heel (from 104-155 ms) but enhanced by metatarsal (from 76-128 ms) stimuli. To examine the neural mechanisms mediating this reflex interaction, we conducted two further experiments to probe potential contributions from (1) presynaptic inhibition, and (2) modulations at the ⍺- and γ-motoneuron pools. Results suggest the cutaneous interactions with the stretch reflex pathway required a modulation at the ⍺-motoneuron pool and were likely not mediated by presynaptic inhibition. These findings demonstrate that foot sole cutaneous information functionally tunes the stretch reflex pathway during the control of upright posture and balance.
我们研究了足底足跟和跖骨区域的皮肤反馈对站立时比目鱼肌牵张反射通路的影响。我们发现，脚跟电刺激抑制，而跖骨刺激增强比目鱼肌的振动反应。后续实验表明，足底皮肤反馈与比目鱼肌振动反应之间的相互作用可能不是由突触前抑制介导的，而是取决于 ⍺-运动神经元池水平的调制。足底皮肤反馈与比目鱼肌振动反应之间的空间组织相互作用提供了关于感觉信息如何组合以适当响应站立时的扰动的信息。
足底皮肤反馈提供与平衡相关的信息，并有可能与脊髓反射通路相互作用。在这项研究中，我们研究了足底皮肤反馈（足跟和跖骨）如何影响站立时比目鱼肌对本体感受刺激的反应。当我们间歇性地将电脉冲序列（200 Hz 时的五个 1 ms 脉冲，每 0.8-1.0 s）施加到对侧足底足跟或跖骨下方的皮肤时，我们向右侧跟腱施加噪声振动（10-115 Hz）。我们分析了振动加速度与整流比目鱼肌肌电图之间的时变（参照皮肤刺激）相干性和互相关。在 ∼10-80 Hz 的带宽内观察到振动-肌电图相干性，并且足跟皮肤刺激抑制了相干性，而跖骨皮肤刺激增强了相干性。互相关显示比目鱼肌肌电图与振动（∼40 ms 滞后）相关，并且足跟刺激（104-155 ms）抑制了互相关，而跖骨刺激（76-128 ms）增强了互相关。为了研究介导这种反射相互作用的神经机制，我们进行了另外两项实验来探测潜在的贡献：（1）突触前抑制，以及（2） ⍺-和 γ-运动神经元池的调制。结果表明，与伸展反射通路的皮肤相互作用需要在 ⍺-运动神经元池进行调制，并且可能不是由突触前抑制介导的。这些发现表明，在控制直立姿势和平衡时，足底皮肤信息可以调节伸展反射通路。
