脑底部的多巴胺神经元是正常运动行为的关键，它们的损失会导致帕金森氏症等疾病。然而，多巴胺神经元的活性与身体运动无关，而是与奖励事件有关。最近的理论表明，多巴胺神经元作为一个同质的功能集团通过与奖励相关的信号来引导运动学习。
现在，用对“正”刺激和“负”刺激做出巴甫洛夫条件反射的猴子所做的一项研究表明，多巴胺神经元比这一模型所暗示的异质性要更强一些。位于脑中稍有不同的区域中的不同类别的多巴胺神经元，对愉快的和不愉快的刺激有特定反应，对与这些事件相关的诱发刺激也有特定反应。这表明，多巴胺神经元在学习控制中的参与情况要更为复杂，它们所编码的信号也要比简单的奖励更为微妙。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature 459, 837-841 (11 June 2009) | doi:10.1038/nature08028
Two types of dopamine neuron distinctly convey positive and negative motivational signals
Masayuki Matsumoto1 & Okihide Hikosaka1
Laboratory of Sensorimotor Research, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892-4435, USA
Midbrain dopamine neurons are activated by reward or sensory stimuli predicting reward1, 2, 3, 4. These excitatory responses increase as the reward value increases5. This response property has led to a hypothesis that dopamine neurons encode value-related signals and are inhibited by aversive events. Here we show that this is true only for a subset of dopamine neurons. We recorded the activity of dopamine neurons in monkeys (Macaca mulatta) during a Pavlovian procedure with appetitive and aversive outcomes (liquid rewards and airpuffs directed at the face, respectively). We found that some dopamine neurons were excited by reward-predicting stimuli and inhibited by airpuff-predicting stimuli, as the value hypothesis predicts. However, a greater number of dopamine neurons were excited by both of these stimuli, inconsistent with the hypothesis. Some dopamine neurons were also excited by both rewards and airpuffs themselves, especially when they were unpredictable. Neurons excited by the airpuff-predicting stimuli were located more dorsolaterally in the substantia nigra pars compacta, whereas neurons inhibited by the stimuli were located more ventromedially, some in the ventral tegmental area. A similar anatomical difference was observed for their responses to actual airpuffs. These findings suggest that different groups of dopamine neurons convey motivational signals in distinct manners.
