Department of Biology, Neurobiology, University of KonstanzKonstanz, Germany.
Front Neural Circuits. 2017 Jun 20;11:42. doi: 10.3389/fncir.2017.00042. eCollection 2017.
Dopaminergic neurons (DANs) signal punishment and reward during associative learning. In mammals, DANs show associative plasticity that correlates with the discrepancy between predicted and actual reinforcement (prediction error) during classical conditioning. Also in insects, such as , DANs show associative plasticity that is, however, less understood. Here, we study associative plasticity in DANs and their synaptic partners, the Kenyon cells (KCs) in the mushroom bodies (MBs), while training to associate an odorant with a temporally separated electric shock (trace conditioning). In most MB compartments DANs strengthened their responses to the conditioned odorant relative to untrained animals. This response plasticity preserved the initial degree of similarity between the odorant- and the shock-induced spatial response patterns, which decreased in untrained animals. Contrary to DANs, KCs (α'/β'-type) decreased their responses to the conditioned odorant relative to untrained animals. We found no evidence for prediction error coding by DANs during conditioning. Rather, our data supports the hypothesis that DAN plasticity encodes conditioning-induced changes in the odorant's predictive power.
多巴胺能神经元（DANs）在联想学习过程中传递惩罚和奖励信号。在哺乳动物中，DANs 表现出与经典条件作用过程中预测和实际强化之间差异（预测误差）相关的联想可塑性。同样，在昆虫中，例如，DANs 表现出联想可塑性，但这种可塑性的理解还不够深入。在这里，我们研究了在蘑菇体（MB）中的多巴胺能神经元（DANs）及其突触伙伴，肯尼恩细胞（KCs）的联想可塑性，同时训练 对一种气味与时间上分离的电击（痕迹条件作用）进行关联。在大多数 MB 隔室中，DANs 相对于未经训练的动物增强了对条件气味的反应。这种反应可塑性保持了气味诱导的空间反应模式与电击诱导的空间反应模式之间初始相似性的程度，而未经训练的动物则降低了这种相似性。与 DANs 相反，KCs（α'/β'-型）相对于未经训练的动物减少了对条件气味的反应。我们没有发现 DANs 在条件作用过程中编码预测误差的证据。相反，我们的数据支持这样一种假设，即 DAN 可塑性编码了气味预测能力的条件作用诱导变化。
