Morrison Sara E, Bamkole Michael A, Nicola Saleem M
Department of Psychiatry and Behavioral Science, Albert Einstein College of Medicine Bronx, NY, USA.
Department of Psychiatry and Behavioral Science, Albert Einstein College of MedicineBronx, NY, USA; Dominick P. Purpura Department of Neuroscience, Albert Einstein College of MedicineBronx, NY, USA.
Front Neurosci. 2015 Dec 16;9:468. doi: 10.3389/fnins.2015.00468. eCollection 2015.
During Pavlovian conditioning, a conditioned stimulus (CS) may act as a predictor of a reward to be delivered in another location. Individuals vary widely in their propensity to engage with the CS (sign tracking) or with the site of eventual reward (goal tracking). It is often assumed that sign tracking involves the association of the CS with the motivational value of the reward, resulting in the CS acquiring incentive value independent of the outcome. However, experimental evidence for this assumption is lacking. In order to test the hypothesis that sign tracking behavior does not rely on a neural representation of the outcome, we employed a reward devaluation procedure. We trained rats on a classic Pavlovian paradigm in which a lever CS was paired with a sucrose reward, then devalued the reward by pairing sucrose with illness in the absence of the CS. We found that sign tracking behavior was enhanced, rather than diminished, following reward devaluation; thus, sign tracking is clearly independent of a representation of the outcome. In contrast, goal tracking behavior was decreased by reward devaluation. Furthermore, when we divided rats into those with high propensity to engage with the lever (sign trackers) and low propensity to engage with the lever (goal trackers), we found that nearly all of the effects of devaluation could be attributed to the goal trackers. These results show that sign tracking and goal tracking behavior may be the output of different associative structures in the brain, providing insight into the mechanisms by which reward-associated stimuli-such as drug cues-come to exert control over behavior in some individuals.
在巴甫洛夫条件反射过程中，条件刺激（CS）可能作为另一个位置即将给予奖励的预测信号。个体在与条件刺激（信号追踪）或最终奖励位置（目标追踪）互动的倾向上差异很大。人们通常认为，信号追踪涉及条件刺激与奖励的动机价值的关联，导致条件刺激获得独立于结果的激励价值。然而，缺乏支持这一假设的实验证据。为了检验信号追踪行为不依赖于结果的神经表征这一假设，我们采用了奖励贬值程序。我们在经典的巴甫洛夫范式中训练大鼠，其中杠杆条件刺激与蔗糖奖励配对，然后在没有条件刺激的情况下，通过将蔗糖与疾病配对来使奖励贬值。我们发现，奖励贬值后，信号追踪行为增强而非减弱；因此，信号追踪显然独立于结果的表征。相比之下，目标追踪行为因奖励贬值而减少。此外，当我们将大鼠分为与杠杆互动倾向高的（信号追踪者）和与杠杆互动倾向低的（目标追踪者）时，我们发现几乎所有贬值效应都可归因于目标追踪者。这些结果表明，信号追踪和目标追踪行为可能是大脑中不同联想结构的输出，为与奖励相关的刺激（如药物线索）在某些个体中对行为施加控制的机制提供了见解。
