Department of Physical Education and Sport Sciences, University of Limerick, Limerick, Ireland.
Exp Brain Res. 2011 Feb;208(4):581-93. doi: 10.1007/s00221-010-2506-x. Epub 2010 Dec 8.
In muscle responses of proprioceptive origin, including the stretch/tendon reflex (T-reflex), the corresponding reciprocal excitation and irradiation to distant muscles have been described from newborn infants to older adults. However, the functioning of other responses mediated primarily by Ia-afferents has not been investigated in infants. Understanding the typical development of these multiple pathways is critical to determining potential problems in their development in populations affected by neurological disease, such as spina bifida or cerebral palsy. Hence, the goal of the present study was to quantify the excitability of Ia-mediated responses in lower limb muscles of infants with typical development. These responses were elicited by mechanical stimulation applied to the distal tendons of the gastrocnemius-soleus (GS), tibialis anterior (TA) and quadriceps (QAD) muscles of both legs in twelve 2- to 10-month-old infants and recorded simultaneously in antagonist muscle pairs by surface EMG. Tendon taps alone elicited responses in either, both or neither muscle. The homonymous response (T-reflex) was less frequent in the TA than the GS or QAD muscle. An 80 Hz vibration superimposed on tendon taps induced primarily an inhibition of monosynaptic responses; however, facilitation also occurred in either muscle of the recorded pair. These responses were not influenced significantly by age or gender. Vibration alone produced a tonic reflex response in the vibrated muscle (TVR) and/or the antagonist muscle (AVR). However, for the TA muscle the TVR was more frequently elicited in older than younger infants. High variability was common to all responses. Overall, the random distribution and inconsistency of muscle responses suggests that the gain of Ia-mediated feedback is unstable. We propose that during infancy the central nervous system needs to learn to set stable feedback gain, or destination of proprioceptive assistance, based on their use during functional movements. This will tailor the neuromuscular connectivity to support adaptive motor behaviors.
在本体感受来源的肌肉反应中，包括拉伸/肌腱反射（T 反射），在新生儿到老年人中已经描述了相应的对远处肌肉的反向兴奋和辐射。然而，主要由 Ia 传入纤维介导的其他反应的功能尚未在婴儿中进行研究。了解这些多途径的典型发育对于确定受神经疾病影响的人群（如脊柱裂或脑瘫）中其发育潜在问题至关重要。因此，本研究的目的是量化具有典型发育的婴儿下肢肌肉中 Ia 介导反应的兴奋性。这些反应是通过机械刺激施加到双侧小腿的跟腱-腓肠肌（GS）、胫骨前肌（TA）和股四头肌（QAD）的远端肌腱来诱发的，并通过表面肌电图同时在拮抗肌对中记录。单独的肌腱叩击会在一个、两个或都不会引发肌肉反应。同形同反射（T 反射）在 TA 中的出现频率低于 GS 或 QAD 肌肉。叠加在肌腱叩击上的 80 Hz 振动主要诱导单突触反应的抑制；然而，在记录的对中任一个肌肉也会发生易化。这些反应不受年龄或性别影响。单独的振动会在振动肌肉（TVR）和/或拮抗肌肉（AVR）中产生紧张反射反应。然而，对于 TA 肌肉，TVR 在年龄较大的婴儿中比年龄较小的婴儿更频繁地被引出。所有反应的高变异性很常见。总体而言，肌肉反应的随机分布和不一致表明 Ia 介导的反馈增益不稳定。我们提出，在婴儿期，中枢神经系统需要学会根据功能性运动中的使用来设置稳定的反馈增益或本体感觉辅助的目标。这将调整神经肌肉连接以支持适应性运动行为。
