Russo G S, Bruce C J
Section of Neurobiology, Yale University School of Medicine, New Haven, Connecticut 06520-8001, USA.
J Neurophysiol. 2000 Nov;84(5):2605-21. doi: 10.1152/jn.2000.84.5.2605.
The functional organization of the low-threshold supplementary eye field (SEF) was studied by analyzing presaccadic activity, electrically elicited saccades, and the relationship between them. Response-field optimal vectors, defined as the visual field coordinates or saccadic eye-movement dimensions evoking the highest neural discharge, were quantitatively estimated for 160 SEF neurons by systematically varying peripheral target location relative to a central fixation point and then fitting the responses to Gaussian functions. Saccades were electrically elicited at 109 SEF sites by microstimulation (70 ms, 10-100 microA) during central fixation. The distribution of response fields and elicited saccades indicated a complete representation of all contralateral saccades in SEF. Elicited saccade polar directions ranged between 97 and 262 degrees (data from left hemispheres were transformed to a right-hemisphere convention), and amplitudes ranged between 1.8 and 26.9 degrees. Response-field optimal vectors (right hemisphere transformed) were nearly all contralateral as well; the directions of 115/119 visual response fields and 80/84 movement response fields ranged between 90 and 279 degrees, and response-field eccentricities ranged between 5 and 50 degrees. Response-field directions for the visual and movement activity of visuomovement neurons were strongly correlated (r = 0.95). When neural activity and elicited saccades obtained at exactly the same sites were compared, response fields were highly predictive of elicited saccade dimensions. Response-field direction was highly correlated with the direction of saccades elicited at the recording site (r = 0.92, n = 77). Similarly, response-field eccentricity predicted the size of subsequent electrically elicited saccades (r = 0.49, n = 60). However, elicited saccades were generally smaller than response-field eccentricities and consistently more horizontal when response fields were nearly vertical. The polar direction of response fields and elicited saccades remained constant perpendicular to the cortical surface, indicating a columnar organization of saccade direction. Saccade direction progressively shifted across SEF; however, these orderly shifts were more indicative of a hypercolumnar organization rather than a single global topography. No systematic organization for saccade amplitude was evident. We conclude that saccades are represented in SEF by congruent visual receptive fields, presaccadic movement fields, and efferent mappings. Thus SEF specifies saccade vectors as bursts of activity by local groups of neurons with appropriate projections to downstream oculomotor structures. In this respect, SEF is organized like the superior colliculus and the frontal eye field even though SEF lacks an overall global saccade topography. We contend that all specialized oculomotor functions of SEF must operate within the context of this fundamental organization.
通过分析扫视前活动、电诱发扫视及其之间的关系，对低阈值辅助眼区（SEF）的功能组织进行了研究。通过系统地改变相对于中央注视点的周边目标位置，然后将反应拟合为高斯函数，对160个SEF神经元定量估计了反应场最佳向量，该向量定义为引起最高神经放电的视野坐标或扫视眼动维度。在中央注视期间，通过微刺激（70毫秒，10 - 100微安）在109个SEF位点电诱发扫视。反应场和诱发扫视的分布表明SEF中对所有对侧扫视有完整的表征。诱发扫视的极角范围在97至262度之间（来自左半球的数据转换为右半球惯例），幅度范围在1.8至26.9度之间。反应场最佳向量（转换后的右半球）几乎也都是对侧的；115/119个视觉反应场和80/84个运动反应场的方向范围在90至279度之间，反应场偏心率范围在5至50度之间。视觉运动神经元的视觉和运动活动的反应场方向高度相关（r = 0.95）。当比较在完全相同位点获得的神经活动和诱发扫视时，反应场对诱发扫视维度具有高度预测性。反应场方向与在记录位点诱发的扫视方向高度相关（r = 0.92，n = 77）。同样，反应场偏心率预测了随后电诱发扫视的大小（r = 0.49，n = 60）。然而，诱发扫视通常小于反应场偏心率，并且当反应场接近垂直时，诱发扫视始终更偏向水平。反应场和诱发扫视的极角方向始终垂直于皮质表面，表明扫视方向存在柱状组织。扫视方向在SEF中逐渐变化；然而，这些有序变化更表明是一种超柱状组织而非单一的全局地形图。扫视幅度没有明显的系统组织。我们得出结论，扫视在SEF中由一致的视觉感受野、扫视前运动场和传出映射来表征。因此，SEF通过具有向下游动眼结构的适当投射的局部神经元群的活动爆发来指定扫视向量。在这方面，SEF的组织方式类似于上丘和额叶眼区，尽管SEF缺乏整体的全局扫视地形图。我们认为SEF的所有特殊动眼功能都必须在这个基本组织的背景下运作。
