Lünenburger Lars, Lindner Werner, Hoffmann Klaus-Peter
Allgemeine Zoologie und Neurobiologie, Ruhr-Universität Bochum, D-44780 Bochum, Germany.
Prog Brain Res. 2003;142:91-107. doi: 10.1016/S0079-6123(03)42008-6.
Although primates including humans can do 2-3 saccades per second while observing their environment, this seems to be more complicated when the same visual target is displaced twice in brief succession. When the subject has to follow this target with its gaze, the reaction time of the second saccade is longer than that of the first. We present data from electrophysiological recordings in the superior colliculus of a monkey that is performing a double-step saccade task. Analysis of the neuronal activity shows that the fixation neurons and the saccadic neurons respond differently in single- and double-step tasks. Fixation neurons are not as active between the two saccades as could be expected from single-step trials. Therefore, the fixation neurons are not likely to cause the increase in reaction time. The recorded saccadic neurons usually showed a presumably visual activation about 70 ms after target appearance and a motor burst starting briefly before the saccade. A target-aligned response was encountered in half of the neurons about 150 ms after the second target appearance. The early visual target-aligned response is often lost before the second saccade in a double-step task with short stimulus delay. The rise of activity was slower before the second than before the first saccade. The neural latency was therefore longer before the second saccade. The motor burst coincides with the second saccade although it is delayed. Thus, the motor burst was always predictive of the occurrence of the saccade. We conclude that the fixation neurons in the superior colliculus are not likely to cause the delay of the second saccade, and that the activity in the saccadic neurons in the superior colliculus encodes the timing of the second saccade even if it is delayed.
虽然包括人类在内的灵长类动物在观察周围环境时每秒能进行2 - 3次扫视，但当同一个视觉目标在短时间内连续两次移动时，情况似乎会变得更加复杂。当受试者必须用目光追踪这个目标时，第二次扫视的反应时间比第一次长。我们展示了一只正在执行双步扫视任务的猴子上丘的电生理记录数据。对神经元活动的分析表明，在单步和双步任务中，注视神经元和扫视神经元的反应不同。在两次扫视之间，注视神经元的活跃程度不如单步试验预期的那样高。因此，注视神经元不太可能导致反应时间增加。记录的扫视神经元通常在目标出现后约70毫秒显示出大概的视觉激活，并在扫视前短暂开始出现运动爆发。在第二个目标出现后约150毫秒，一半的神经元出现了与目标对齐的反应。在刺激延迟较短的双步任务中，早期视觉目标对齐反应在第二次扫视之前常常消失。第二次扫视前活动的上升比第一次扫视前更慢。因此，第二次扫视前的神经潜伏期更长。尽管运动爆发有延迟，但它与第二次扫视同时发生。所以，运动爆发总是能预测扫视的发生。我们得出结论，上丘中的注视神经元不太可能导致第二次扫视延迟，并且上丘中扫视神经元的活动即使在延迟的情况下也编码了第二次扫视的时间。
