Vandaele Youna, Pribut Heather J, Janak Patricia H
Department of Psychological and Brain Sciences, Krieger School of Arts and Sciences, Johns Hopkins University, Baltimore, MD, United States.
The Solomon H. Snyder Department of Neuroscience, Johns Hopkins School of Medicine, Johns Hopkins University, Baltimore, MD, United States.
Front Integr Neurosci. 2017 Sep 27;11:23. doi: 10.3389/fnint.2017.00023. eCollection 2017.
Flexible and efficient decision-making in complex environments can be achieved through constant interactions between the goal-directed and habitual systems. While goal-directed behavior is considered dependent upon Response-Outcome (R-O) associations, habits instead rely on Stimulus-Response (S-R) associations. However, the stimuli that support the S-R association underlying habitual responding in typical instrumental procedures are poorly defined. To resolve this issue, we designed a discrete-trials procedure, in which rats must wait for lever insertion and complete a sequence of five lever presses to obtain a reward (20% sucrose or grain-based pellets). Lever insertion thus constituted an audio-visual stimulus signaling the opportunity for reward. Using sensory-specific satiety-induced devaluation, we found that rats trained with grain-based pellets remained sensitive to outcome devaluation over the course of training with this procedure whereas rats trained with a solution of 20% sucrose rapidly developed habit, and that insensitivity to outcome devaluation in rats trained with sucrose did not result from a bias in general satiety. Importantly, although rats trained with pellets were sensitive to satiety-induced devaluation, their performance was not affected by degradation of instrumental contingency and devaluation by conditioned taste aversion (CTA), suggesting that these rats may also have developed habitual responding. To test whether the discrete-trials procedure biases subjects towards habitual responding, we compared discrete-trials to free-running instrumental responding, and found that rats trained with sucrose in a fixed-ratio 5 (FR5) procedure with continuous presentation of the lever were goal-directed. Together, these results demonstrate that discrete presentations of a stimulus predictive of reward availability promoted the formation of S-R habit in rats trained with liquid sucrose. Further research is necessary to explain inconsistencies in sensitivity to outcome devaluation when rats are trained with grain-based pellets.
在复杂环境中，灵活高效的决策可以通过目标导向系统和习惯系统之间的持续相互作用来实现。虽然目标导向行为被认为依赖于反应-结果（R-O）关联，但习惯则依赖于刺激-反应（S-R）关联。然而，在典型的工具性程序中，支持习惯性反应背后的S-R关联的刺激却定义不明确。为了解决这个问题，我们设计了一种离散试验程序，在该程序中，大鼠必须等待杠杆插入，并完成一系列五次杠杆按压才能获得奖励（20%蔗糖或谷物颗粒）。因此，杠杆插入构成了一种视听刺激，表明有获得奖励的机会。使用感官特异性饱腹感诱导的贬值，我们发现，在用谷物颗粒训练的大鼠中，在该程序的训练过程中，它们对结果贬值仍然敏感，而用20%蔗糖溶液训练的大鼠则迅速形成习惯，并且用蔗糖训练的大鼠对结果贬值不敏感并非源于一般饱腹感的偏差。重要的是，尽管用颗粒训练的大鼠对饱腹感诱导的贬值敏感，但它们的表现不受工具性偶然性的降低和条件性味觉厌恶（CTA）导致的贬值的影响，这表明这些大鼠也可能已经形成了习惯性反应。为了测试离散试验程序是否会使受试者倾向于习惯性反应，我们将离散试验与自由运行的工具性反应进行了比较，发现用蔗糖在固定比率5（FR5）程序中连续呈现杠杆进行训练的大鼠是目标导向的。总之，这些结果表明，预测奖励可用性的刺激的离散呈现促进了用液体蔗糖训练的大鼠中S-R习惯的形成。当用谷物颗粒训练大鼠时，需要进一步研究来解释对结果贬值敏感性的不一致性。
