Tremblay L, Hollerman J R, Schultz W
Institute of Physiology, University of Fribourg, CH-1700 Fribourg, Switzerland.
J Neurophysiol. 1998 Aug;80(2):964-77. doi: 10.1152/jn.1998.80.2.964.
This study investigated neuronal activity in the anterior striatum while monkeys repeatedly learned to associate new instruction stimuli with known behavioral reactions and reinforcers. In a delayed go-nogo task with several trial types, an initial picture instructed the animal to execute or withhold a reaching movement and to expect a liquid reward or not. During learning, new instruction pictures were presented, and animals guessed and performed one of the trial types according to a trial-and-error strategy. Learning of a large number of pictures resulted in a learning set in which learning took place in a few trials and correct performance exceeded 80% in the first 60-90 trials. About 200 task-related striatal neurons studied in both familiar and learning conditions showed three forms of changes during learning. Activations related to the preparation and execution of behavioral reactions and the expectation of reward were maintained in many neurons but occurred in inappropriate trial types when behavioral errors were made. The activations became appropriate for individual trial types when the animals' behavior adapted to the new task contingencies. In particular, reward expectation-related activations occurred initially in both rewarded and unrewarded movement trials and became subsequently restricted to rewarded trials. These changes occurred in parallel with the visible adaptation of reward expectations by the animals. The second learning change consisted in decreases of task-related activations that were either restricted to the initial trials of new learning problems or persisted during the subsequent consolidation phase. They probably reflected reductions in the expectation and preparation of upcoming task events, including reward. The third learning change consisted in transient or sustained increases of activations. These might reflect the increased attention accompanying learning and serve to induce synaptic changes underlying the behavioral adaptations. Both decreases and increases often induced changes in the trial selective occurrence of activations. In conclusion, neurons in anterior striatum showed changes related to adaptations or reductions of expectations in new task situations and displayed activations that might serve to induce structural changes during learning.
本研究调查了猴子在反复学习将新的指令刺激与已知行为反应及强化物建立联系时，前纹状体中的神经元活动。在一个具有多种试验类型的延迟“去/不去”任务中，最初的图片指示动物执行或抑制伸手动作，并预期是否会得到液体奖励。在学习过程中，呈现新的指令图片，动物根据试错策略猜测并执行其中一种试验类型。对大量图片的学习形成了一个学习集，在此学习集中，只需几次试验就能完成学习，且在前60 - 90次试验中正确表现超过80%。在熟悉和学习两种条件下研究的约200个与任务相关的纹状体神经元在学习过程中表现出三种变化形式。许多神经元中与行为反应的准备和执行以及奖励预期相关的激活在学习过程中得以维持，但当出现行为错误时，这些激活会出现在不适当的试验类型中。当动物的行为适应新的任务条件时，这些激活会变得适合于各个试验类型。特别是，与奖励预期相关的激活最初在有奖励和无奖励的动作试验中都会出现，随后会局限于有奖励的试验。这些变化与动物明显的奖励预期适应过程同时发生。第二种学习变化表现为与任务相关的激活减少，这种减少要么局限于新学习问题的初始试验，要么在随后的巩固阶段持续存在。它们可能反映了对即将到来的任务事件（包括奖励）的预期和准备的减少。第三种学习变化表现为激活的短暂或持续增加。这些可能反映了学习过程中注意力的增强，并有助于诱导行为适应背后的突触变化。减少和增加通常都会导致激活在试验选择性出现方面的变化。总之，前纹状体中的神经元表现出与新任务情境中预期的适应或减少相关的变化，并显示出可能有助于在学习过程中诱导结构变化的激活。
