McGill University, Department of Physiology, 3655 Sir William Osler, Montreal, Quebec H3G 1Y6, Canada.
J Neurophysiol. 2011 Feb;105(2):661-73. doi: 10.1152/jn.00788.2010. Epub 2010 Dec 8.
Plasticity in neuronal responses is necessary for compensation following brain lesions and adaptation to new conditions and motor learning. In a previous study, we showed that compensatory changes in the vestibuloocular reflex (VOR) following unilateral vestibular loss were characterized by dynamic reweighting of inputs from vestibular and extravestibular modalities at the level of single neurons that constitute the first central stage of VOR signal processing. Here, we studied another class of neurons, i.e., the vestibular-only neurons, in the vestibular nuclei that mediate vestibulospinal reflexes and provide information for higher brain areas. We investigated changes in the relative contribution of vestibular, neck proprioceptive, and efference copy signals in the response of these neurons during compensation after contralateral vestibular loss in Macaca mulata monkeys. We show that the time course of recovery of vestibular sensitivity of neurons corresponds with that of lower extremity muscle and tendon reflexes reported in previous studies. More important, we found that information from neck proprioceptors, which did not influence neuronal responses before the lesion, were unmasked after lesion. Such inputs influenced the early stages of the compensation process evidenced by faster and more substantial recovery of the resting discharge in proprioceptive-sensitive neurons. Interestingly, unlike our previous study of VOR interneurons, the improvement in the sensitivity of the two groups of neurons did not show any difference in the early or late stages after lesion. Finally, neuronal responses during active head movements were not different before and after lesion and were attenuated relative to passive movements over the course of recovery, similar to that observed in control conditions. Comparison of compensatory changes observed in the vestibuloocular and vestibulospinal pathways provides evidence for similarities and differences between the two classes of neurons that mediate these pathways at the functional and cellular levels.
神经元反应的可塑性对于脑损伤后的代偿、适应新的条件和运动学习是必要的。在之前的研究中，我们表明单侧前庭损失后前庭眼反射（VOR）的代偿变化的特征是在构成 VOR 信号处理的第一中央阶段的单个神经元水平上，来自前庭和前庭外模态的输入的动态重新加权。在这里，我们研究了另一种神经元，即前庭核中的前庭神经元，它们介导前庭脊髓反射，并为大脑更高区域提供信息。我们研究了在猕猴对侧前庭损失后的代偿过程中，这些神经元反应中前庭、颈部本体感觉和传出复制信号的相对贡献的变化。我们表明，神经元前庭敏感性的恢复时间与以前研究中报道的下肢肌肉和肌腱反射的恢复时间相对应。更重要的是，我们发现，在损伤前不影响神经元反应的颈部本体感受器的信息在损伤后被揭示出来。这些输入影响补偿过程的早期阶段，表现为本体感觉敏感神经元的静息放电更快、更实质性的恢复。有趣的是，与我们之前对 VOR 中间神经元的研究不同，两组神经元的敏感性改善在损伤后的早期或晚期阶段没有显示出任何差异。最后，在损伤前后，主动头部运动期间的神经元反应与被动运动相比没有差异，并且在恢复过程中相对于被动运动减弱，这与在对照条件下观察到的情况相似。对前庭眼和前庭脊髓通路中观察到的代偿变化的比较为介导这些通路的两类神经元在功能和细胞水平上的相似性和差异性提供了证据。
