Schiller Peter H, Tehovnik Edward J
Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, E25-634, Cambridge, MA 02139, USA.
Prog Brain Res. 2005;149:157-71. doi: 10.1016/S0079-6123(05)49012-3.
In exploring the visual scene we make about three saccadic eye movements per second. During each fixation, in addition to analyzing the object at which we are looking, a decision has to be made as to where to look next. Although we perform this task with the greatest of ease, the computations to perform the task are complex and involve numerous brain structures. We have applied several investigative tools that include single-cell recordings, microstimulation, pharmacological manipulations and lesions to learn more about the neural control of visually guided eye saccadic movements. Electrical stimulation of the superior colliculus (SC), areas V1 and V2, the lateral intraparietal sulcus (LIP), the frontal eye fields (FEF) and the medial eye fields (MEF) produces saccadic eye movements at low current levels. After ablation of the SC, electrical microstimulation of V1, V2, and LIP no longer elicits saccadic eye movements whereas stimulation of the FEF and MEF continues to be effective. Ablation of the SC but not of the FEF eliminates short-latency saccadic eye movements to visual targets called "express saccades," whereas lesions of the FEF selectively interfere with target selection. Bilateral removal of both the SC and the FEF causes major, long lasting deficits: all visually elicited saccadic eye movements are eliminated. In intact monkeys, subthreshold electrical microstimulation of the FEF and MEF as well as the lower layers of V1 and V2 and of some subregions of LIP greatly facilitates the choice of targets presented in the receptive fields of the stimulated neurons. By contrast, stimulation of the upper layers of V1 and V2 and other sub-regions of LIP produces a dramatic interference in target selection. Examination of the role of inhibitory circuits in eye-movement generation reveals that local infusion of muscimol, a GABA (gamma-aminobutyric acid) agonist, or bicuculline, a GABA antagonist, interferes with target selection in V1. On the other hand, infusion of bicuculline into the FEF produces facilitation in target choice and irrepressible saccades. It appears therefore that inhibitory circuits play a central role in visual analysis in V1 and in the generation of saccadic eye movements in the FEF. It is proposed that two major streams can be discerned in visually guided eye-movement control, the posterior from occipital and parietal cortex that reaches the brainstem via the SC and the anterior from the FEF and MEF that has direct access to the brainstem oculomotor centers.
在探索视觉场景时，我们每秒大约会进行三次眼球扫视运动。在每次注视期间，除了分析我们正在注视的物体外，还必须决定接下来看向何处。尽管我们轻松地执行这项任务，但执行该任务的计算很复杂，涉及众多脑结构。我们应用了多种研究工具，包括单细胞记录、微刺激、药物操作和损伤，以更多地了解视觉引导眼球扫视运动的神经控制。对上丘（SC）、V1和V2区域、顶内沟外侧（LIP）、额叶眼区（FEF）和内侧眼区（MEF）进行电刺激，在低电流水平下会产生眼球扫视运动。在切除SC后，对V1、V2和LIP进行电微刺激不再引发眼球扫视运动，而对FEF和MEF的刺激仍然有效。切除SC而非FEF会消除对称为“快速扫视”的视觉目标的短潜伏期眼球扫视运动，而FEF的损伤会选择性地干扰目标选择。双侧切除SC和FEF会导致严重的、长期的缺陷：所有视觉诱发的眼球扫视运动都会被消除。在完整的猴子中，对FEF和MEF以及V1和V2的下层和LIP的一些子区域进行阈下电微刺激，极大地促进了在受刺激神经元感受野中呈现的目标的选择。相比之下，刺激V1和V2的上层以及LIP的其他子区域会对目标选择产生显著干扰。对抑制性回路在眼球运动产生中的作用的研究表明，局部注入GABA（γ-氨基丁酸）激动剂蝇蕈醇或GABA拮抗剂荷包牡丹碱会干扰V1中的目标选择。另一方面，向FEF中注入荷包牡丹碱会促进目标选择并产生无法抑制的扫视运动。因此，抑制性回路似乎在V1的视觉分析和FEF中眼球扫视运动的产生中起着核心作用。有人提出，在视觉引导的眼球运动控制中可以辨别出两条主要通路，一条是从枕叶和顶叶皮质向后经SC到达脑干，另一条是从FEF和MEF向前直接通向脑干动眼神经中枢。
