Syed Anam, Baker Phillip M, Ragozzino Michael E
Department of Psychology, University of Illinois at Chicago, 1007 West Harrison Street, Chicago, IL 60607-7137, United States.
Department of Psychology, University of Illinois at Chicago, 1007 West Harrison Street, Chicago, IL 60607-7137, United States; Graduate Program in Neuroscience, University of Illinois at Chicago, Chicago, IL 60607, United States.
Neurobiol Learn Mem. 2016 May;131:1-8. doi: 10.1016/j.nlm.2016.03.010. Epub 2016 Mar 11.
Recent findings indicate that pedunculopontine tegmental nucleus (PPTg) neurons encode reward-related information that is context-dependent. This information is critical for behavioral flexibility when reward outcomes change signaling a shift in response patterns should occur. The present experiment investigated whether NMDA lesions of the PPTg affects the acquisition and/or reversal learning of a spatial discrimination using probabilistic reinforcement. Male Long-Evans rats received a bilateral infusion of NMDA (30nmoles/side) or saline into the PPTg. Subsequently, rats were tested in a spatial discrimination test using a probabilistic learning procedure. One spatial location was rewarded with an 80% probability and the other spatial location rewarded with a 20% probability. After reaching acquisition criterion of 10 consecutive correct trials, the spatial location - reward contingencies were reversed in the following test session. Bilateral and unilateral PPTg-lesioned rats acquired the spatial discrimination test comparable to that as sham controls. In contrast, bilateral PPTg lesions, but not unilateral PPTg lesions, impaired reversal learning. The reversal learning deficit occurred because of increased regressions to the previously 'correct' spatial location after initially selecting the new, 'correct' choice. PPTg lesions also reduced the frequency of win-stay behavior early in the reversal learning session, but did not modify the frequency of lose-shift behavior during reversal learning. The present results suggest that the PPTg contributes to behavioral flexibility under conditions in which outcomes are uncertain, e.g. probabilistic reinforcement, by facilitating sensitivity to positive reward outcomes that allows the reliable execution of a new choice pattern.
最近的研究结果表明，脚桥被盖核（PPTg）神经元编码与奖励相关的信息，且该信息依赖于情境。当奖励结果发生变化时，这种信息对于行为灵活性至关重要，这表明反应模式应发生转变。本实验研究了PPTg的N-甲基-D-天冬氨酸（NMDA）损伤是否会影响使用概率强化的空间辨别学习的获得和/或反转学习。雄性Long-Evans大鼠双侧脑内注入NMDA（30纳摩尔/侧）或生理盐水到PPTg。随后，使用概率学习程序在空间辨别测试中对大鼠进行测试。一个空间位置有80%的概率获得奖励，另一个空间位置有20%的概率获得奖励。在达到连续10次正确试验的习得标准后，在下一个测试阶段反转空间位置 - 奖励的意外情况。双侧和单侧PPTg损伤的大鼠在空间辨别测试中的习得情况与假手术对照组相当。相比之下，双侧PPTg损伤而非单侧PPTg损伤会损害反转学习。反转学习缺陷的出现是因为在最初选择新的“正确”选择后，对先前“正确”空间位置的回归增加。PPTg损伤还降低了反转学习阶段早期赢留行为的频率，但并未改变反转学习期间输移行为的频率。目前的结果表明，PPTg通过促进对积极奖励结果的敏感性，从而有助于在结果不确定的条件下（如概率强化）实现行为灵活性，进而能够可靠地执行新的选择模式。
