Successive negative contrast (SNC) has been used to study reward relativity, reward loss, and frustration for decades. In instrumental SNC (iSNC), the anticipatory performance of animals downshifted from a large reward to a small reward is compared to that of animals always reinforced with the small reward. iSNC involves a transient deterioration of anticipatory behavior in downshifted animals compared to unshifted controls. There is scattered information on the optimal parameters to produce this effect and even less information about its neural basis. Five experiments with rats trained in a runway to collect food pellets explored the effects of trial distribution (massed or spaced), amount of preshift training, reward disparity, and reward magnitude on the development of an iSNC effect. Start, run, and goal latencies were measured. Using spaced trials (one trial per day), evidence of the iSNC effect was observed with 24 preshift trials and a 32-to-4 pellet disparity. With massed trials (4 trials per session separated by 30-s intertrial intervals), evidence of iSNC was found with 12 preshift sessions (a total of 48 trials) and a 16-to-2 pellet disparity. The massed-training procedure was then used to assess neural activity in three prefrontal cortex areas using c-Fos expression in animals perfused after the first downshift session. There was evidence of increased activation in the anterior cingulate cortex and a trend toward increased activation in the infralimbic and prelimbic cortices. These procedures open a venue for studying the neural basis of the instrumental behavior of animals that experience reward loss.

中文翻译：

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大鼠仪器连续负对比：试验分布、奖励幅度和前额皮质激活

几十年来，连续负对比（SNC）一直被用来研究奖励相对性、奖励损失和挫败感。在工具性 SNC (iSNC) 中，将动物的预期表现从大奖励下调至小奖励与始终用小奖励强化的动物进行比较。与未转变的对照组相比，iSNC 涉及降低转变的动物的预期行为的短暂恶化。关于产生这种效果的最佳参数的信息是分散的，关于其神经基础的信息甚至更少。对在跑道上训练老鼠收集食物颗粒的五项实验探讨了试验分布（集中或间隔）、轮班前训练量、奖励差异和奖励幅度对 iSNC 效应发展的影响。测量启动、运行和目标延迟。使用间隔试验（每天一次试验），通过 24 次轮班前试验和 32 比 4 的颗粒差异观察到 iSNC 效应的证据。通过集中试验（每次 4 次试验，试验间隔 30 秒），在 12 次轮班前试验（总共 48 次试验）和 16 比 2 的颗粒差异中发现了 iSNC 的证据。然后使用集中训练程序来评估三个前额皮质区域的神经活动，使用第一次降档后灌注的动物中的 c-Fos 表达。有证据表明前扣带皮层的激活增加，并且边缘下和前边缘皮质的激活有增加的趋势。这些程序为研究经历奖励损失的动物的工具行为的神经基础开辟了一个场所。