Laboratory of Neuropsychology, National Institute of Mental Health, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland 20892, USA.
J Neurosci. 2012 May 16;32(20):6869-77. doi: 10.1523/JNEUROSCI.0887-12.2012.
In humans and other animals, the vigor with which a reward is pursued depends on its desirability, that is, on the reward's predicted value. Predicted value is generally context-dependent, varying according to the value of rewards obtained in the recent and distant past. Signals related to reward prediction and valuation are believed to be encoded in a circuit centered around midbrain dopamine neurons and their targets in the prefrontal cortex and basal ganglia. Notably absent from this hypothesized reward pathway are dopaminergic targets in the medial temporal lobe. Here we show that a key part of the medial temporal lobe memory system previously reported to be important for sensory mnemonic and perceptual processing, the rhinal cortex (Rh), is required for using memories of previous reward values to predict the value of forthcoming rewards. We tested monkeys with bilateral Rh lesions on a task in which reward size varied across blocks of uncued trials. In this experiment, the only cues for predicting current reward value are the sizes of rewards delivered in previous blocks. Unexpectedly, monkeys with Rh ablations, but not intact controls, were insensitive to differences in predicted reward, responding as if they expected all rewards to be of equal magnitude. Thus, it appears that Rh is critical for using memory of previous rewards to predict the value of forthcoming rewards. These results are in agreement with accumulating evidence that Rh is critical for establishing the relationships between temporally interleaved events, which is a key element of episodic memory.
在人类和其他动物中，对奖励的追求力度取决于其吸引力，也就是说，取决于奖励的预期价值。预期价值通常取决于上下文，根据最近和过去的奖励价值而变化。据信，与奖励预测和估值相关的信号是由中脑多巴胺神经元及其在前额叶皮层和基底神经节中的目标为中心的回路编码的。从中脑多巴胺神经元到内侧颞叶的多巴胺能目标在这个假设的奖励途径中明显缺失。在这里，我们展示了内侧颞叶记忆系统的一个关键部分，以前的研究表明它对感觉记忆和感知处理很重要，即梨状皮层（Rh），对于利用以前的奖励价值记忆来预测即将到来的奖励的价值是必需的。我们在一项任务中测试了双侧 Rh 损伤的猴子，在该任务中，奖励大小在无提示试验的块之间变化。在这个实验中，预测当前奖励价值的唯一线索是前几个块中传递的奖励的大小。出乎意料的是，Rh 切除的猴子，而不是完整的对照猴子，对预测奖励的差异不敏感，就好像它们预期所有奖励的大小都相等一样。因此，似乎 Rh 对于利用以前的奖励记忆来预测即将到来的奖励的价值至关重要。这些结果与越来越多的证据一致，即 Rh 对于建立时间上交织的事件之间的关系至关重要，这是情景记忆的一个关键要素。
