Pickens Charles L
Department of Psychological and Brain Sciences, Johns Hopkins University, USA.
Behav Neurosci. 2008 Jun;122(3):659-76. doi: 10.1037/0735-7044.122.3.659.
Six experiments were performed to determine the role of mediodorsal thalamus (MD) in the devaluation task, varying the type of contingencies (Pavlovian or operant), the number of reinforcers (one vs. two), and the order of experiments (in naïve or experimentally experienced rats). MD-lesioned rats were impaired in devaluation performance when switched between Pavlovian and operant devaluation tasks, but not when switched from one Pavlovian devaluation task to another Pavlovian devaluation task. MD lesions caused no devaluation impairment in a multiple-reinforcer Pavlovian devaluation task. These results suggest that MD lesions impair performance in devaluation tasks as a result of an inability to switch the form of associations made from one type of outcome-encoding association to another. This is in accord with previous literature suggesting that MD is needed for strategy set shifting. The results further suggest that MD is a necessary part of devaluation circuits only in cases in which previous associations need to be suppressed in order for new associations to be learned and control behavior, and otherwise the devaluation circuit does not require MD.
进行了六项实验以确定丘脑背内侧核（MD）在贬值任务中的作用，实验改变了偶然性的类型（经典条件反射或操作性条件反射）、强化物的数量（一个与两个）以及实验顺序（针对未经过训练或有实验经验的大鼠）。当在经典条件反射和操作性贬值任务之间切换时，MD损伤的大鼠在贬值表现上受损，但从一个经典条件反射贬值任务切换到另一个经典条件反射贬值任务时则没有受损。MD损伤在多强化物经典条件反射贬值任务中未导致贬值损伤。这些结果表明，MD损伤会损害贬值任务中的表现，原因是无法将形成的关联形式从一种结果编码关联切换到另一种。这与先前的文献一致，即策略集转换需要MD。结果进一步表明，只有在需要抑制先前关联以便学习新关联并控制行为的情况下，MD才是贬值回路的必要组成部分，否则贬值回路不需要MD。
