Van Horn Marion R, Sylvestre Pierre A, Cullen Kathleen E
Aerospace Medical Research Unit, Department of Physiology, McGill University, 3655 Promenade Sir William Osler, Montreal, PQ, Canada.
J Neurophysiol. 2008 May;99(5):2602-16. doi: 10.1152/jn.01379.2007. Epub 2008 Mar 12.
When we look between objects located at different depths the horizontal movement of each eye is different from that of the other, yet temporally synchronized. Traditionally, a vergence-specific neuronal subsystem, independent from other oculomotor subsystems, has been thought to generate all eye movements in depth. However, recent studies have challenged this view by unmasking interactions between vergence and saccadic eye movements during disconjugate saccades. Here, we combined experimental and modeling approaches to address whether the premotor command to generate disconjugate saccades originates exclusively in "vergence centers." We found that the brain stem burst generator, which is commonly assumed to drive only the conjugate component of eye movements, carries substantial vergence-related information during disconjugate saccades. Notably, facilitated vergence velocities during disconjugate saccades were synchronized with the burst onset of excitatory and inhibitory brain stem saccadic burst neurons (SBNs). Furthermore, the time-varying discharge properties of the majority of SBNs (>70%) preferentially encoded the dynamics of an individual eye during disconjugate saccades. When these experimental results were implemented into a computer-based simulation, to further evaluate the contribution of the saccadic burst generator in generating disconjugate saccades, we found that it carries all the vergence drive that is necessary to shape the activity of the abducens motoneurons to which it projects. Taken together, our results provide evidence that the premotor commands from the brain stem saccadic circuitry, to the target motoneurons, are sufficient to ensure the accurate control shifts of gaze in three dimensions.
当我们观察位于不同深度的物体之间时，每只眼睛的水平运动彼此不同，但在时间上是同步的。传统上，人们认为存在一个独立于其他眼球运动子系统的、特定于辐辏的神经元子系统，它能产生所有的深度眼球运动。然而，最近的研究通过揭示非共轭扫视期间辐辏和扫视眼球运动之间的相互作用，对这一观点提出了挑战。在这里，我们结合实验和建模方法，以探讨产生非共轭扫视的运动前指令是否仅起源于“辐辏中枢”。我们发现，通常被认为仅驱动眼球运动共轭成分的脑干爆发发生器，在非共轭扫视期间携带大量与辐辏相关的信息。值得注意的是，非共轭扫视期间促进的辐辏速度与兴奋性和抑制性脑干扫视爆发神经元（SBNs）的爆发起始同步。此外，大多数SBNs（>70%）的时变放电特性在非共轭扫视期间优先编码单只眼睛的动态变化。当将这些实验结果应用于基于计算机的模拟中，以进一步评估扫视爆发发生器在产生非共轭扫视中的作用时，我们发现它携带了塑造其投射到的外展运动神经元活动所需的所有辐辏驱动。综上所述，我们的结果提供了证据，表明从脑干扫视回路到目标运动神经元的运动前指令足以确保在三维空间中精确控制注视转移。
