Doctoral Program in Kansei, Behavioral and Brain Sciences, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan.
PLoS One. 2012;7(1):e30190. doi: 10.1371/journal.pone.0030190. Epub 2012 Jan 18.
The value of a predicted reward can be estimated based on the conjunction of both the intrinsic reward value and the length of time to obtain it. The question we addressed is how the two aspects, reward size and proximity to reward, influence the responses of neurons in rostral anterior cingulate cortex (rACC), a brain region thought to play an important role in reward processing.
We recorded from single neurons while two monkeys performed a multi-trial reward schedule task. The monkeys performed 1-4 sequential color discrimination trials to obtain a reward of 1-3 liquid drops. There were two task conditions, a valid cue condition, where the number of trials and reward amount were associated with visual cues, and a random cue condition, where the cue was picked from the cue set at random. In the valid cue condition, the neuronal firing is strongly modulated by the predicted reward proximity during the trials. Information about the predicted reward amount is almost absent at those times. In substantial subpopulations, the neuronal responses decreased or increased gradually through schedule progress to the predicted outcome. These two gradually modulating signals could be used to calculate the effect of time on the perception of reward value. In the random cue condition, little information about the reward proximity or reward amount is encoded during the course of the trial before reward delivery, but when the reward is actually delivered the responses reflect both the reward proximity and reward amount.
Our results suggest that the rACC neurons encode information about reward proximity and amount in a manner that is dependent on utility of reward information. The manner in which the information is represented could be used in the moment-to-moment calculation of the effect of time and amount on predicted outcome value.
奖励的价值可以根据内在奖励价值和获得奖励所需的时间的结合来估计。我们要解决的问题是，奖励大小和接近奖励的两个方面如何影响额前扣带皮质（rACC）神经元的反应，rACC 被认为在奖励处理中起着重要作用。
当两只猴子执行一个多试次奖励时间表任务时，我们记录了单个神经元的活动。猴子执行 1-4 次连续颜色辨别试验，以获得 1-3 滴液体奖励。有两种任务条件，一种是有效线索条件，其中试验的次数和奖励金额与视觉线索相关联，另一种是随机线索条件，其中线索是从线索集中随机选择的。在有效线索条件下，神经元的放电在试验过程中强烈地受到预测奖励接近度的调制。在那些时候，关于预测奖励金额的信息几乎不存在。在大量的亚群中，神经元的反应通过计划进展到预测结果逐渐减少或增加。这两个逐渐调制的信号可以用来计算时间对奖励价值感知的影响。在随机线索条件下，在奖励交付之前的试验过程中，关于奖励接近度或奖励金额的信息几乎没有被编码，但当奖励实际交付时，反应反映了奖励的接近度和数量。
我们的结果表明，rACC 神经元以一种依赖于奖励信息效用的方式编码奖励接近度和数量的信息。信息的表示方式可以用于即时计算时间和数量对预测结果价值的影响。
