Chan Y S
Department of Physiology, Faculty of Medicine, The University of Hong Kong.
Exp Brain Res. 1997 Apr;114(2):293-303. doi: 10.1007/pl00005638.
In decerebrate cats that had been acutely hemilabyrinthectomized (HL), the extracellular activities of vestibular nuclear neurons on the lesioned and labyrinth-intact sides were studied during constant-velocity off-vertical axis rotations (OVAR) in the clockwise (CW) and counterclockwise (CCW) directions (at 10 degrees tilt). Over the range of 1.75-15 degrees/s, two types of neuronal responses were identified on both sides. Some neurons showed symmetric and velocity-stable bidirectional response sensitivity (delta defined as the CW gain over the CCW gain) while other neurons exhibited asymmetric and velocity-variable delta. The mathematically derived gain tuning ratios of these two groups of neurons were within the range of one-dimensional and two-dimensional neurons respectively. The best response orientations in one-dimensional neurons and the orientations of the maximum response vector, S(max), in two-dimensional neurons were found to point in all directions on the horizontal plane. On the labyrinth-intact side, both the one-dimensional and two-dimensional neurons showed asymmetry in the neuron numbers and/or the response gains between the two roll quadrants as well as between the two pitch quadrants. In addition, both the neuron number and gain were significantly higher for neurons in the head-down/ipsilateral-side-down half-circle than those in the head-up/contralateral-side-down half-circle. None of the aforementioned asymmetries was observed on the lesioned side. That a comparable pattern of distribution was observed in the one-dimensional and two-dimensional neurons suggests that these neurons maintain a common spatial reference frame in encoding head orientational signals arising from the ipsilateral and contralateral otoliths. Furthermore, a predominance of two-dimensional neurons that exhibited a greater gain with CW rotations was observed on both sides of HL cats. Of the response dynamics observed amongst neurons on the two sides of HL cats, no difference was found with regard to the response gain and the pattern of response lead. However, a difference in response lag was observed between neurons on the two sides of HL cats. These suggest that there is a segregation of otolithic signals to reach the ipsilateral and contralateral vestibular nuclei. Taken together, the present study demonstrates that one-dimensional and two-dimensional neuronal responses could be elicited with inputs arising solely from the ipsilateral or contralateral otoliths. The observed orientational tuning and the CW-CCW asymmetry to bidirectional rotation may provide the essential directional coding of head orientations. Further, the imbalance of spatial/dynamic response patterns between the bilateral vestibular nuclei following the restriction of otolith inputs by HL implies that converging otolithic inputs from the bilateral labyrinths are essential for producing the neuronal responses in control animals. The results are also discussed in terms of the possible contribution of the various neural asymmetries between neuronal subpopulations in the bilateral vestibular nuclei to the behavioral symptoms accompanying acute HL.
在急性半规管切除（HL）的去大脑猫中，研究了在10度倾斜下以顺时针（CW）和逆时针（CCW）方向进行等速非垂直轴旋转（OVAR）时，损伤侧和迷路完整侧前庭核神经元的细胞外活动。在1.75 - 15度/秒的范围内，两侧均识别出两种类型的神经元反应。一些神经元表现出对称且速度稳定的双向反应敏感性（δ定义为CW增益与CCW增益之比），而其他神经元则表现出不对称且速度可变的δ。这两组神经元的数学推导增益调谐比分别在一维神经元和二维神经元的范围内。发现一维神经元的最佳反应方向和二维神经元中最大反应向量S(max)的方向在水平面上指向所有方向。在迷路完整侧，一维和二维神经元在两个滚转象限以及两个俯仰象限之间的神经元数量和/或反应增益上均表现出不对称性。此外，头朝下/同侧朝下半圆中的神经元数量和增益均显著高于头朝上/对侧朝下半圆中的神经元。在损伤侧未观察到上述任何不对称性。在一维和二维神经元中观察到类似的分布模式，这表明这些神经元在编码来自同侧和对侧耳石的头部定向信号时维持一个共同的空间参考框架。此外，在HL猫的两侧均观察到二维神经元在CW旋转时表现出更大增益的优势。在HL猫两侧的神经元中观察到的反应动力学中，在反应增益和反应领先模式方面未发现差异。然而，在HL猫两侧的神经元之间观察到反应滞后的差异。这些表明耳石信号在到达同侧和对侧前庭核时有分离。综上所述，本研究表明，仅来自同侧或对侧耳石的输入即可引发一维和二维神经元反应。观察到的定向调谐和对双向旋转的CW - CCW不对称性可能提供头部定向的基本方向编码。此外，HL限制耳石输入后双侧前庭核之间空间/动态反应模式的不平衡意味着来自双侧迷路的汇聚耳石输入对于在对照动物中产生神经元反应至关重要。还根据双侧前庭核中神经元亚群之间各种神经不对称性对急性HL伴随的行为症状的可能贡献来讨论结果。
