Isoda Masaki, Hikosaka Okihide
Laboratory of Sensorimotor Research, National Eye Institute, National Institutes of Health, Bethesda, Maryland, USA.
J Neurophysiol. 2008 Sep;100(3):1332-42. doi: 10.1152/jn.90275.2008. Epub 2008 Jul 2.
Behavior is controlled by both external instructions and internal motives, but the actions demanded by each may be different. A common consequence of such a conflict is a delay in decision making and subsequent motor responses. It is unknown, however, what neural mechanisms underlie motivational conflict and associated response delay. To answer this question, we recorded single-neuron activity in the superior colliculus (SC) as macaque monkeys performed a visually guided, asymmetrically rewarded saccade task. A peripheral spot of light at one of two opposing positions was illuminated to indicate a saccade target. In a given block of trials, one position was associated with a big reward and the other with a small reward. The big-reward position was alternated across blocks. Behavioral analyses revealed that small-reward trials created a conflict between the instructed saccade to one position and the internally motivated, yet invalid saccade to the opposite position. We found that movement neurons in the SC temporally exhibited bursting activity after the appearance of the small-reward target opposite their movement field. This transient activity predicted the amount of response delay for upcoming saccades. Our data suggest that motivational conflict activates movement neurons in both colliculi, thereby delaying saccade initiation through intercollicular inhibitory interactions.
行为受外部指令和内部动机的双重控制，但两者所要求的行动可能有所不同。这种冲突的一个常见后果是决策延迟以及随后的运动反应延迟。然而，尚不清楚是什么神经机制构成了动机冲突及相关的反应延迟。为了回答这个问题，我们在猕猴执行视觉引导的、非对称奖励的扫视任务时，记录了上丘（SC）中的单神经元活动。两个相对位置之一的外周光点被照亮以指示扫视目标。在给定的试验块中，一个位置与大奖励相关联，另一个位置与小奖励相关联。大奖励位置在各试验块之间交替。行为分析表明，小奖励试验在指示扫视到一个位置与内部驱动但无效的扫视到相反位置之间产生了冲突。我们发现，上丘中的运动神经元在其运动视野对面出现小奖励目标后，在时间上表现出爆发性活动。这种瞬时活动预测了即将进行的扫视的反应延迟量。我们的数据表明，动机冲突激活了两个上丘中的运动神经元，从而通过上丘间的抑制性相互作用延迟了扫视的起始。
