Van Horn Marion R, Cullen Kathleen E
Aerospace Medical Research Unit, Department of Physiology, McGill University, Montreal, Quebec, Canada.
J Neurophysiol. 2009 Jul;102(1):28-40. doi: 10.1152/jn.00169.2009. Epub 2009 Apr 29.
In this report, we provide the first quantitative characterization of the relationship between the spike train dynamics of medial rectus oculomotoneurons (OMNs) and eye movements during conjugate and disconjugate saccades. We show that a simple, first-order model (i.e., containing eye position and velocity terms) provided an adequate model of neural discharges during both on and off-directed conjugate saccades, while a second-order model, which included a decaying slide term, significantly improved the ability to fit neuronal responses by approximately 10% (P<0.05). To understand how the same neurons drove disconjugate eye movements, we evaluated whether sensitivities estimated during conjugate saccades could be used to predict responses during disconjugate saccades. For the majority of neurons (68%), a conjugate-based model failed, and instead neurons preferentially encoded the position and velocity of the ipsilateral eye. Similar to our previous results with abducens motoneurons, we also found that position and velocity sensitivities of OMNs decreased with increasing velocity, and the simulated population drive of OMNs during disconjugate saccades was less (approximately 10%) than during conjugate saccades. Taken together, our results provide evidence that the activation of the antagonist, as well as agonist, motoneuron pools must be considered to understand the neural control of horizontal eye movements across different oculomotor behaviors. Moreover, we propose that the undersampling of smaller motoneurons (e.g., nontwitch) was likely to account for the missing drive observed during disconjugate saccades; these cells are thought to be more specialized for vergence movements and thus could provide the additional input required to command disconjugate eye movements.
在本报告中，我们首次对内侧直肌动眼运动神经元（OMNs）的放电序列动态与共轭和非共轭扫视期间的眼球运动之间的关系进行了定量表征。我们发现，一个简单的一阶模型（即包含眼位和速度项）能够为同向和反向共轭扫视期间的神经放电提供充分的模型，而包含衰减滑动项的二阶模型则显著提高了拟合神经元反应的能力，提升幅度约为10%（P<0.05）。为了理解相同的神经元如何驱动非共轭眼球运动，我们评估了共轭扫视期间估计的敏感性是否可用于预测非共轭扫视期间的反应。对于大多数神经元（68%），基于共轭的模型并不适用，相反，神经元优先编码同侧眼的位置和速度。与我们之前关于外展运动神经元的结果类似，我们还发现，OMNs的位置和速度敏感性随着速度增加而降低，并且非共轭扫视期间OMNs的模拟群体驱动比共轭扫视期间少（约10%）。综上所述，我们的结果表明，为了理解不同眼动行为中水平眼球运动的神经控制，必须考虑拮抗肌以及主动肌运动神经元池的激活。此外，我们提出，较小运动神经元（如非抽搐性运动神经元）的采样不足可能是导致非共轭扫视期间观察到的驱动缺失的原因；这些细胞被认为更专门用于辐辏运动，因此可以提供指挥非共轭眼球运动所需的额外输入。
