Meachum C L
University of Cambridge, U.K.
Q J Exp Psychol B. 1990 May;42(2):175-95.
Three experiments investigated what role a novel incentive plays in the development of operant response suppression mediated by lithium chloride. In all experiments animals were trained to press two levers under concurrent schedules of reinforcement. In Experiment 1 responding on one lever delivered a familiar incentive (food pellets), whereas responding on an alternative lever delivered a novel incentive (sucrose solution) prior to lithium chloride injections. If lithium was administered immediately after the instrumental session, the action associated with the novel, but not with the familiar, incentive was suppressed. By comparison, in a control group for which responding on both levers led to the familiar incentive, both actions were suppressed. Experiment 2 examined whether the novelty, rather than the sensory properties, of the incentive is crucial for observing performance suppression. It was found that animals familiarized with the "target" incentive were insensitive to aversion conditioning by lithium, in that there was no difference in response rates between the action that delivered the familiar incentive from that which earned the "target". In contrast, if animals were unfamiliar with the "target" incentive at the time of aversion conditioning, they suppressed responding on the lever that was associated with the novel incentive but did not suppress responding on the lever associated with the familiar incentive. Experiment 3 investigated the mechanism underlying instrumental performance suppression. After the completion of concurrent lever press training, novel sucrose was introduced in conjunction with the pellets for responding on one lever; responding on the other lever continued to deliver only familiar pellets. Lithium injections were then administered either immediately following the sessions or several hours after the sessions. It was found that the rate of responding on the lever associated with the contingent delivery of sucrose was suppressed below that of the pellet-alone action. By comparison, if lithium injections were administered several hours following the session, an elevation in responding on the sucrose-plus-pellet lever was observed. The outcomes of all three experiments demonstrate not only that the novelty of an incentive is important in obtaining performance suppression, but also that a novel incentive can punish instrumental responding if it has been associated with toxicosis.
三项实验研究了一种新型刺激在由氯化锂介导的操作性反应抑制发展过程中所起的作用。在所有实验中，动物被训练在同时进行的强化程序下按压两个杠杆。在实验1中，在注射氯化锂之前，按压一个杠杆会得到一种熟悉的刺激（食丸），而按压另一个杠杆会得到一种新型刺激（蔗糖溶液）。如果在工具性训练后立即给予锂，与新型刺激相关的行为，而不是与熟悉刺激相关的行为，会受到抑制。相比之下，在一个对照组中，按压两个杠杆都会导致熟悉的刺激，两种行为都受到了抑制。实验2检验了刺激的新颖性而非感官特性对于观察到行为抑制是否至关重要。结果发现，熟悉“目标”刺激的动物对锂引起的厌恶条件作用不敏感，即提供熟悉刺激的行为与获得“目标”刺激的行为之间的反应率没有差异。相反，如果动物在厌恶条件作用时不熟悉“目标”刺激，它们会抑制与新型刺激相关的杠杆上的反应，但不会抑制与熟悉刺激相关的杠杆上的反应。实验3研究了工具性表现抑制的潜在机制。在同时进行的杠杆按压训练完成后，将新型蔗糖与食丸一起用于一个杠杆的反应；另一个杠杆的反应继续只提供熟悉的食丸。然后在训练后立即或训练后数小时给予锂注射。结果发现，与蔗糖意外递送相关的杠杆上的反应率被抑制到低于仅食丸行为的反应率。相比之下，如果在训练后数小时给予锂注射，则会观察到蔗糖加食丸杠杆上的反应增加。所有三项实验的结果不仅表明刺激的新颖性在获得行为抑制方面很重要，而且还表明如果新型刺激与中毒相关，它可以惩罚工具性反应。
