Watanabe Masataka, Hikosaka Kazuo, Sakagami Masamichi, Shirakawa Shu-ichiro
Department of Psychology, Tokyo Metropolitan Institute for Neuroscience, Fuchu, Tokyo 183-8526, Japan.
J Neurosci. 2002 Mar 15;22(6):2391-400. doi: 10.1523/JNEUROSCI.22-06-02391.2002.
The prefrontal cortex is involved in acquiring and maintaining information about context, including the set of task instructions and/or the outcome of previous stimulus-response sequences. Most studies on context-dependent processing in the prefrontal cortex have been concerned with such executive functions, but the prefrontal cortex is also involved in motivational operations. We thus wished to determine whether primate prefrontal neurons show evidence of representing the motivational context learned by the monkey. We trained monkeys in a delayed reaction task in which an instruction cue indicated the presence or absence of reward. In random alternation with no reward, the same one of several different kinds of food and liquid rewards was delivered repeatedly in a block of approximately 50 trials, so that reward information would define the motivational context. In response to an instruction cue indicating absence of reward, we found that neurons in the lateral prefrontal cortex not only predicted the absence of reward but also represented more specifically which kind of reward would be omitted in a given trial. These neurons seem to code contextual information concerning which kind of reward may be delivered in following trials. We also found prefrontal neurons that showed tonic baseline activity that may be related to monitoring such motivational context. The different types of neurons were distributed differently along the dorsoventral extent of the lateral prefrontal cortex. Such operations in the prefrontal cortex may be important for the monkey to maximize reward or to modify behavioral strategies and thus may contribute to executive control.
前额叶皮层参与获取和维持有关情境的信息，包括任务指令集和/或先前刺激-反应序列的结果。大多数关于前额叶皮层中情境依赖加工的研究都关注此类执行功能，但前额叶皮层也参与动机性操作。因此，我们希望确定灵长类动物前额叶神经元是否表现出代表猴子所学动机情境的证据。我们训练猴子进行延迟反应任务，其中一个指令线索表明奖励的有无。在无奖励的随机交替中，几种不同类型的食物和液体奖励中的同一种会在大约50次试验的一个组块中反复发放，以便奖励信息能够定义动机情境。在对指示无奖励的指令线索做出反应时，我们发现外侧前额叶皮层中的神经元不仅预测无奖励，而且更具体地代表在给定试验中会省略哪种奖励。这些神经元似乎编码了关于后续试验中可能发放哪种奖励的情境信息。我们还发现前额叶神经元表现出紧张性基线活动，这可能与监测这种动机情境有关。不同类型的神经元沿外侧前额叶皮层的背腹范围分布不同。前额叶皮层中的此类操作可能对猴子最大化奖励或修改行为策略很重要，因此可能有助于执行控制。
