McPeek Robert M, Keller Edward L
The Smith-Kettlewell Eye Research Institute, San Francisco, California 94115, USA.
J Neurophysiol. 2002 Apr;87(4):1805-15. doi: 10.1152/jn.00501.2001.
Saccades are typically separated by inter-saccadic fixation intervals (ISFIs) of > or =125 ms. During this time, the saccadic system selects a goal and completes the preparatory processes required prior to executing the subsequent movement. However, in tasks in which competing stimuli are presented, two sequentially executed movements to different goals can be separated by much shorter ISFIs. This suggests that the saccadic system is capable of completing many of the preparatory requirements for a second saccade concurrently with the execution of an initial movement. We recorded single neurons in the superior colliculus (SC) during rapid saccade sequences made by rhesus monkeys performing a search task. We found that during the execution of an initial saccade, activity related to the goal of a quickly following second saccade can be simultaneously maintained in the SC motor map. This activity appears to signal the selection or increased salience of the second saccade goal even before the initial saccade has ended. For movements separated by normal ISFIs (> or =125 ms), we did not observe activity related to concurrent processing, presumably because for these longer ISFI responses, the goal of the second saccade is not selected until after the end of the first saccade. These results indicate that, at the time of an initial saccade, the SC does not necessarily act as a strict winner-take-all network. Rather it appears that the salience of a second visual goal can be simultaneously maintained in the SC. This provides evidence that selection or preparatory activity related to the goal of a second saccade can overlap temporally with activity related to an initial saccade and indicates that such concurrent processing is present even in a structure which is fairly close to the motor output.
扫视通常由大于或等于125毫秒的扫视间注视间隔（ISFIs）分隔。在此期间，扫视系统选择一个目标并完成执行后续动作之前所需的准备过程。然而，在呈现竞争性刺激的任务中，两个依次执行到不同目标的动作可以由短得多的ISFIs分隔。这表明扫视系统能够在执行初始动作的同时，完成对第二次扫视的许多准备要求。我们在恒河猴执行搜索任务时进行快速扫视序列期间，记录了上丘（SC）中的单个神经元。我们发现，在执行初始扫视期间，与快速跟随的第二次扫视目标相关的活动可以在上丘运动图谱中同时维持。即使在初始扫视结束之前，这种活动似乎也在表明第二次扫视目标的选择或显著性增加。对于由正常ISFIs（大于或等于125毫秒）分隔的动作，我们没有观察到与并行处理相关的活动，大概是因为对于这些较长的ISFI反应，第二次扫视的目标直到第一次扫视结束后才被选择。这些结果表明，在初始扫视时，上丘不一定作为严格的胜者全得网络起作用。相反，似乎第二个视觉目标的显著性可以在上丘中同时维持。这提供了证据，表明与第二次扫视目标相关的选择或准备活动可以在时间上与与初始扫视相关的活动重叠，并表明即使在相当接近运动输出的结构中也存在这种并行处理。
