ANALYSIS OF A NATURALLY-OCCURRING ASYMMETRY IN VERTICAL SMOOTH PURSUIT EYE-MOVEMENTS IN A MONKEY
ANALYSIS OF A NATURALLY-OCCURRING ASYMMETRY IN VERTICAL SMOOTH PURSUIT EYE-MOVEMENTS IN A MONKEY
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DOI：
10.1152/jn.1992.67.1.164
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发表时间：
1992-01-01
影响因子：
2.5
通讯作者：
LISBERGER, SG
中科院分区：
文献类型：
--
作者：
GRASSE, KL;LISBERGER, SG
1. 我们已经调查了一个猴子的垂直追求眼球运动的方向性赤字的机制，是无法匹配向上的眼球速度的目标速度，但在正常范围内的向下或水平的目标运动的追求。 除了缺乏追求轴的差异，这只猴子的症状与人类或猴子大脑皮层额叶或顶叶病变相似。 我们对这只猴子的垂直追踪的评估为额叶和顶叶在追踪中的作用提出了一个新的解释。 上/下的不对称性是最明显的目标运动速度大于或等于2度/秒。 对于15或30度/秒的目标运动，向上的阶梯斜坡目标运动引起了短暂的向上平滑的眼睛加速度，其次是跟踪，主要包括扫视。 向下步进斜坡目标运动诱发了长时间的平滑眼加速度，随后是平滑、准确的跟踪. 改变目标步骤的幅度显示，赤字是类似的目标移动跨越所有位置的视野。 在间隔0-20 ms的眼加速度开始追求后是独立的初始目标位置，是对称的向上和向下的目标运动。 眼加速度在间隔60-80毫秒后开始追求表现出很大的不对称性。 对于向上的目标运动，在这个时间间隔内的眼睛加速度很小，并不依赖于初始目标位置。 对于向下运动的目标，眼动加速度强烈依赖于目标的初始位置，当目标开始靠近注视位置时，眼动加速度较大. 接下来，我们试图通过评估猴子在各种跟踪条件下的垂直运动处理和垂直眼球运动来理解上/下不对称的机制。 对于点目标，向上的图像运动的反应是类似的，在正常的猴子，如果图像运动是在向下的追求。 此外，缺乏向上追求的猴子能够使用向上的图像运动来对移动目标进行准确的扫视。 我们的结论是，这只猴子对向上图像运动的视觉处理是正常的，视觉运动处理的不对称不能解释他向上追求的缺陷。5. 当点目标与大纹理图案一起移动时，向上平滑的眼加速度是正常的。 向上和向下的眼球加速度几乎是对称的，猴子能够保持向上的眼球速度，几乎与目标速度相匹配。 我们的结论是，上/下不对称的追求不能归因于缺陷的运动路径，产生向上平滑的眼球运动。 在正常的猴子中，追踪速度记忆自动维持眼速，因此当目标相对于移动的眼睛稳定时，眼速只会缓慢地向零减速。 在猴子与上/下不对称，目标稳定导致眼速度衰减速度在向上比在向下的追求。 然而，在向上的追求过程中的衰减率与正常垂直追求的控制猴子之一相似。 我们的结论是，上/下的不对称性不能归因于缺陷的机制，追求速度记忆。 我们的观察结果表明，一个模型的追求，包括在视觉路径的追求开关。 如果猴子能够关闭向下的开关，但不能关闭向上的目标运动，那么这种模型将说明向上的图像运动的正常处理的不足向上的追求。 类似的解释也可以解释顶叶或额叶皮层受损后水平追踪的方向性缺陷，这表明这些区域在追踪决策中的作用可能比在追踪的直接视觉引导中的作用更大。
1. We have investigated the mechanism of a directional deficit in vertical pursuit eye movements in a monkey that was unable to match upward eye speed to target speed but that had pursuit within the normal range for downward or horizontal target motion. Except for a difference in the axis of deficient pursuit, the symptoms in this monkey were similar to those seen with lesions in the frontal or parietal lobes of the cerebral cortex in humans or monkeys. Our evaluation of vertical pursuit in this monkey suggests a new interpretation for the role of the frontal and parietal lobes in pursuit.2. The up/down asymmetry was most pronounced for target motion at speeds greater-than-or-equal-to 2-degrees /s. For target motion at 15 or 30-degrees /s, upward step-ramp target motion evoked a brief upward smooth eye acceleration, followed by tracking that consisted largely of saccades. Downward step-ramp target motion evoked a prolonged smooth eye acceleration, followed by smooth, accurate tracking.3. Varying the amplitude of the target step revealed that the deficit was similar for targets moving across all locations of the visual field. Eye acceleration in the interval 0-20 ms after the onset of pursuit was independent of initial target position and was symmetrical for upward and downward target motion. Eye acceleration in the interval 60-80 ms after the onset of pursuit showed a large asymmetry. For upward target motion, eye acceleration in this interval was small and did not depend on initial target position. For downward target motion, eye acceleration depended strongly on initial target position and was large when the target started close to the position of fixation.4. We next attempted to understand the mechanism of the up/down asymmetry by evaluating the monkey's vertical motion processing and vertical eye movements under a variety of tracking conditions. For spot targets, the response to upward image motion was similar to that in normal monkeys if the image motion was presented during downward pursuit. In addition, the monkey with deficient upward pursuit was able to use upward image motion to make accurate saccades to moving targets. We conclude that the visual processing of upward image motion was normal in this monkey and that an asymmetry in visual motion processing could not account for the deficit in his upward pursuit.5. Upward smooth eye acceleration was normal when the spot target was moved together with a large textured pattern. Upward and downward eye acceleration were nearly symmetrical, and the monkey was able to maintain upward eye speed that nearly matched target speed. We conclude that the up/down asymmetry in pursuit cannot be attributed to a deficit in the motor pathways that generate upward smooth eye movement.6. In normal monkeys, pursuit velocity memory automatically sustains eye velocity, which therefore decelerates only slowly toward zero when the target is stabilized with respect to the moving eye. In the monkey with the up/down asymmetry, target stabilization caused eye velocity to decay faster during upward than during downward pursuit. However, the rate of decay during upward pursuit was similar to that in one of the control monkeys with normal vertical pursuit. We conclude that the up/down asymmetry cannot be attributed to a deficit in the mechanism of pursuit velocity memory.7. Our observations suggest a model of pursuit that includes a switch in the visuomotor pathways for pursuit. If the monkey were able to close the switch for downward but not for upward target motion, then this kind of model would account for deficient upward pursuit with normal processing of upward image motion. A similar explanation could account for the directional deficits in horizontal pursuit seen after lesions of the parietal or frontal cortex, suggesting that these areas may play a larger role in the decision to pursue than in the direct visual guidance of pursuit.