Brewer Adam, Johnson Patrick, Stein Jeff, Schlund Michael, Williams Dean C
University of Kansas, Lawrence, KS, USA.
California State University, Chico, CA, USA.
Behav Brain Res. 2017 Feb 15;319:174-180. doi: 10.1016/j.bbr.2016.11.025. Epub 2016 Nov 15.
Research on incentive contrast highlights that reward value is not absolute but rather is based upon comparisons we make to rewards we have received and expect to receive. Both human and nonhuman studies on incentive contrast show that shifting from a larger more-valued reward to a smaller less-valued reward is associated with long periods of nonresponding - a negative contrast effect. In this investigation, we used two different genetic rat strains, Fischer 344 and Lewis rats that putatively differ in their sensitivity to aversive stimulation, to assess the aversive properties of large-to-small reward shifts (negative incentive shifts). Additionally, we examined the extent to which increasing cost (fixed-ratio requirements) modulates negative contrast effects. In the presence of a cue that signaled the upcoming reward magnitude, lever pressing was reinforced with one of two different magnitudes of food (large or small). This design created two contrast shifts (small-to-large, large-to-small) and two shifts used as control conditions (small-to-small, large-to-large). Results showed a significant interaction between rat strain and cost requirements only during the negative incentive shift with the emotionally reactive Fischer 344 rats exhibiting significantly longer response latencies with increasing cost, highlighting greater negative contrast. These findings are more consistent with emotionality accounts of negative contrast and results of neurophysiological research that suggests shifting from a large to a small reward is aversive. Findings also highlight how subjective reward value and motivation is a product of gene-environment interactions.
对激励对比的研究强调，奖励价值并非绝对的，而是基于我们对已获得和预期获得的奖励所做的比较。关于激励对比的人类和非人类研究均表明，从更大、更有价值的奖励转向更小、价值较低的奖励会伴随着长时间的无反应——一种负性对比效应。在本研究中，我们使用了两种不同的基因大鼠品系，即假定对厌恶刺激敏感度不同的Fischer 344大鼠和Lewis大鼠，来评估从大奖励到小奖励转变（负性激励转变）的厌恶特性。此外，我们还研究了增加成本（固定比率要求）对负性对比效应的调节程度。在存在预示即将到来的奖励大小的线索的情况下，用两种不同大小的食物（大或小）之一对杠杆按压进行强化。这种设计产生了两种对比转变（小到大、大到小）和两种用作对照条件的转变（小到小、大到大）。结果显示，仅在负性激励转变期间，大鼠品系和成本要求之间存在显著的交互作用，情绪反应性较强的Fischer 344大鼠随着成本增加表现出显著更长的反应潜伏期，突出了更大的负性对比。这些发现与负性对比的情绪理论以及神经生理学研究结果更为一致，后者表明从大奖励转向小奖励是令人厌恶的。研究结果还突出了主观奖励价值和动机是基因-环境相互作用的产物。
