Beckman Vision Center, Program in Neuroscience, University of California San Francisco, San Francisco, California 94143, and.
Center for Mind/Brain Sciences, The University of Trento, Trento, Italy.
J Neurosci. 2018 Jan 3;38(1):173-182. doi: 10.1523/JNEUROSCI.2589-17.2017. Epub 2017 Nov 13.
In subjects with alternating strabismus, either eye can be used to saccade to visual targets. The brain must calculate the correct vector for each saccade, which will depend on the eye chosen to make it. The superior colliculus, a major midbrain center for saccade generation, was examined to determine whether the maps serving each eye were shifted to compensate for strabismus. Alternating exotropia was induced in two male macaques at age 1 month by sectioning the tendons of the medial recti. Once the animals grew to maturity, they were trained to fixate targets with either eye. Receptive fields were mapped in the superior colliculus using a sparse noise stimulus while the monkeys alternated fixation. For some neurons, sparse noise was presented dichoptically to probe for anomalous retinal correspondence. After recordings, microstimulation was applied to compare sensory and motor maps. The data showed that receptive fields were offset in position by the ocular deviation, but otherwise remained aligned. In one animal, the left eye's coordinates were rotated ∼20° clockwise with respect to those of the right eye. This was explained by a corresponding cyclorotation of the ocular fundi, which produced an A-pattern deviation. Microstimulation drove the eyes accurately to the site of receptive fields, as in normal animals. Single-cell recordings uncovered no evidence for anomalous retinal correspondence. Despite strabismus, neurons remained responsive to stimulation of either eye. Misalignment of the eyes early in life does not alter the organization of topographic maps or disrupt binocular convergence in the superior colliculus. Patients with strabismus are able to make rapid eye movements, known as saccades, toward visual targets almost as gracefully as subjects with normal binocular alignment. They can even exercise the option of using the right eye or the left eye. It is unknown how the brain measures the degree of ocular misalignment and uses it to compute the appropriate saccade for either eye. The obvious place to investigate is the superior colliculus, a midbrain oculomotor center responsible for the generation of saccades. Here, we report the first experiments in the superior colliculus of awake primates with strabismus using a combination of single-cell recordings and microstimulation to explore the organization of its topographic maps.
在交替性斜视的受试者中，任何一只眼睛都可以用于向视觉目标扫视。大脑必须计算每次扫视的正确向量，这将取决于用于进行扫视的眼睛。上丘是眼球运动产生的主要中脑中心，我们对其进行了检查，以确定服务于每只眼睛的地图是否会发生偏移，以补偿斜视。通过在 1 个月大时切断内直肌的肌腱，在两只雄性猕猴中诱发交替性外斜视。一旦动物长大成熟，它们就会被训练用任一只眼睛注视目标。当猴子交替注视时，使用稀疏噪声刺激在上丘中绘制感受野。对于一些神经元，使用双目呈现稀疏噪声来探测异常视网膜对应关系。记录后，进行微刺激以比较感觉和运动图。数据表明，感受野的位置因眼球偏转而偏移，但保持对齐。在一只动物中，左眼的坐标相对于右眼顺时针旋转了约 20°。这可以通过眼球底部的相应旋转变位来解释，这产生了 A 型偏位。微刺激可以像正常动物一样，准确地将眼睛驱动到感受野的位置。单细胞记录未发现异常视网膜对应关系的证据。尽管存在斜视，但神经元仍然对任一只眼睛的刺激有反应。生命早期眼睛的错位不会改变上丘的拓扑图组织，也不会破坏双眼会聚。斜视患者能够快速地向视觉目标进行眼球运动，称为扫视，其动作几乎和具有正常双眼对齐的受试者一样优雅。他们甚至可以选择使用右眼或左眼。目前尚不清楚大脑如何测量眼球的错位程度，并利用它来计算任一只眼睛的适当扫视。显然，研究的地方是上丘，这是一个中脑眼球运动中枢，负责产生扫视。在这里，我们报告了在清醒的斜视灵长类动物的上丘中进行的首次实验，使用单细胞记录和微刺激相结合，探索其拓扑图的组织。
