过去曾有人提出，当动物执行简单的刺激-反应任务时，在多巴胺能中脑中所观察到的阶段性活动代表着对即将到来的奖赏的一种预期。现在，Ann Graybiel及其同事演示了纹状体中一种不同形式的与奖赏有关的多巴胺信号作用。采用循环伏安法，他们发现穿越迷宫来获得奖赏的动物的多巴胺信号延长了。这些反应随动物与其目标的接近在稳定增加，同时也随奖赏的距离和大小按比例变化。这些信号可能代表着(对于获得奖赏的)驱动力，有助于我们认识多巴胺在长时间的、由目标引导的行动中所起作用。（生物谷Bioon.com）
生物谷推荐英文摘要：
Nature doi:10.1038/nature12475
Prolonged dopamine signalling in striatum signals proximity and value of distant rewards
Mark W. Howe,Patrick L. Tierney,Stefan G. Sandberg, Paul E. M. Phillips & Ann M. Graybiel
Predictions about future rewarding events have a powerful influence on behaviour. The phasic spike activity of dopamine-containing neurons, and corresponding dopamine transients in the striatum, are thought to underlie these predictions, encoding positive and negative reward prediction errors. However, many behaviours are directed towards distant goals, for which transient signals may fail to provide sustained drive. Here we report an extended mode of reward-predictive dopamine signalling in the striatum that emerged as rats moved towards distant goals. These dopamine signals, which were detected with fast-scan cyclic voltammetry (FSCV), gradually increased or—in rare instances—decreased as the animals navigated mazes to reach remote rewards, rather than having phasic or steady tonic profiles. These dopamine increases (ramps) scaled flexibly with both the distance and size of the rewards. During learning, these dopamine signals showed spatial preferences for goals in different locations and readily changed in magnitude to reflect changing values of the distant rewards. Such prolonged dopamine signalling could provide sustained motivational drive, a control mechanism that may be important for normal behaviour and that can be impaired in a range of neurologic and neuropsychiatric disorders.
