Midbrain dopamine (DA) neurons are involved in the processing of rewards and reward-predicting stimuli, possibly analogous to reinforcement learning reward prediction errors. Here we studied the activity of putative DA neurons (n = 37) recorded in the ventral tegmental area of rats (n = 6) performing a behavioural task involving occasion setting. In this task an occasion setter (OS) indicated that the relationship between a discriminative stimulus (DS) and reinforcement is in effect, so that reinforcement of bar pressing occurred only after the OS (tone or houselight) was followed by the DS (houselight or tone). We found that responses of putative DA cells to the DS were enhanced when preceded by the OS, as were behavioural responses to obtain rewards. Surprisingly though, we did not find a homogeneous increase in the mean activity of the population of putative DA neurons to the OS, contrary to predictions of standard temporal-difference models of DA neurons. Instead, putative DA neurons exhibited a heterogeneous response on a single unit level, so that some units increased and others decreased their activity as a response to the OS. Similarly, putative non-DA cells did not show a homogeneous response to the DS on a population level, but also had heterogeneous responses on a single unit level. The heterogeneity in the responses of neurons in the ventral tegmental area may reflect how DA neurons encode context and point to local differences in DA signalling.

中脑多巴胺（DA）神经元参与奖励和奖励预测刺激的处理，可能类似于强化学习奖励预测错误。在这里，我们研究了在执行涉及情景设置的行为任务的大鼠（n = 6）的腹侧被盖区中记录的假定DA神经元（n = 37）的活动。在此任务中，场合设定者（OS）表示判别性刺激（DS）与加固之间的关系有效，因此，只有在OS（音调或室内照明）之后跟随DS（室内照明或音）。我们发现，在操作系统之前，假定的DA细胞对DS的反应增强了，获得奖励的行为反应也增强了。不过令人惊讶的是 与标准的DA神经元时空模型的预测相反，我们没有发现推定的DA神经元对OS的平均活动均一地增加。取而代之的是，推定的DA神经元在单个单位水平上表现出异质性反应，因此某些单位增加了，而另一些单位则减少了对OS的反应。类似地，推定的非DA细胞在群体水平上没有显示出对DS的均一反应，但在单个单位水平上也表现出了异质性反应。腹侧被盖区神经元反应的异质性可能反映了DA神经元如何编码上下文并指出DA信号传导中的局部差异。推定的DA神经元在单个单位水平上表现出异质性反应，因此某些单位增加，而其他单位则减少其对OS的反应。同样，假定的非DA细胞在群体水平上对DS没有显示出同质反应，但在单个单位水平上却具有异质反应。腹侧被盖区神经元反应的异质性可能反映了DA神经元如何编码上下文并指出DA信号传导中的局部差异。推定的DA神经元在单个单位水平上表现出异质性反应，因此某些单位增加，而其他单位则减少其对OS的反应。同样，假定的非DA细胞在群体水平上对DS没有显示出同质反应，但在单个单位水平上却具有异质反应。腹侧被盖区神经元反应的异质性可能反映了DA神经元如何编码上下文并指出DA信号传导中的局部差异。