Guerrasio Lorenzo, Quinet Julie, Büttner Ulrich, Goffart Laurent
Department of Neurology, Klinikum Groβhadern, LMU, München, Germany.
J Neurophysiol. 2010 Apr;103(4):1988-2001. doi: 10.1152/jn.00771.2009. Epub 2010 Feb 3.
When primates maintain their gaze directed toward a visual target (visual fixation), their eyes display a combination of miniature fast and slow movements. An involvement of the cerebellum in visual fixation is indicated by the severe gaze instabilities observed in patients suffering from cerebellar lesions. Recent studies in non-human primates have identified a cerebellar structure, the fastigial oculomotor region (FOR), as a major cerebellar output nucleus with projections toward oculomotor regions in the brain stem. Unilateral inactivation of the FOR leads to dysmetric visually guided saccades and to an offset in gaze direction when the animal fixates a visual target. However, the nature of this fixation offset is not fully understood. In the present work, we analyze the inactivation-induced effects on fixation. A novel technique is adopted to describe the generation of saccades when a target is being fixated (fixational saccades). We show that the offset is the result of a combination of impaired saccade accuracy and an altered encoding of the foveal target position. Because they are independent, we propose that these two impairments are mediated by the different projections of the FOR to the brain stem, in particular to the deep superior colliculus and the pontomedullary reticular formation. Our study demonstrates that the oculomotor cerebellum, through the activity in the FOR, regulates both the amplitude of fixational saccades and the position toward which the eyes must be directed, suggesting an involvement in the acquisition of visual information from the fovea.
当灵长类动物将目光保持指向视觉目标（视觉注视）时，它们的眼睛会表现出微小快速运动和缓慢运动的组合。小脑损伤患者中观察到的严重注视不稳定表明小脑参与了视觉注视。最近对非人类灵长类动物的研究已确定小脑结构——顶核动眼区（FOR），作为小脑的主要输出核，向脑干中的动眼区投射。单侧失活FOR会导致视觉引导的扫视运动失调，并且当动物注视视觉目标时会导致注视方向偏移。然而，这种注视偏移的本质尚未完全理解。在本研究中，我们分析了失活对注视的影响。采用一种新技术来描述当目标被注视时扫视运动的产生（注视性扫视）。我们表明，这种偏移是扫视准确性受损和中央凹目标位置编码改变共同作用的结果。由于它们是独立的，我们提出这两种损伤是由FOR向脑干的不同投射介导的，特别是向深层上丘和脑桥延髓网状结构的投射。我们的研究表明，动眼小脑通过FOR的活动，调节注视性扫视幅度以及眼睛必须指向的位置，这表明其参与从中央凹获取视觉信息。
