Department of Physiology, University of Bern, Bern, 3012, Switzerland.
Department of Biology, University of Fribourg, Fribourg, 1700, Switzerland.
Sci Rep. 2021 Mar 24;11(1):6795. doi: 10.1038/s41598-021-85841-y.
Olfactory learning and conditioning in the fruit fly is typically modelled by correlation-based associative synaptic plasticity. It was shown that the conditioning of an odor-evoked response by a shock depends on the connections from Kenyon cells (KC) to mushroom body output neurons (MBONs). Although on the behavioral level conditioning is recognized to be predictive, it remains unclear how MBONs form predictions of aversive or appetitive values (valences) of odors on the circuit level. We present behavioral experiments that are not well explained by associative plasticity between conditioned and unconditioned stimuli, and we suggest two alternative models for how predictions can be formed. In error-driven predictive plasticity, dopaminergic neurons (DANs) represent the error between the predictive odor value and the shock strength. In target-driven predictive plasticity, the DANs represent the target for the predictive MBON activity. Predictive plasticity in KC-to-MBON synapses can also explain trace-conditioning, the valence-dependent sign switch in plasticity, and the observed novelty-familiarity representation. The model offers a framework to dissect MBON circuits and interpret DAN activity during olfactory learning.
果蝇的嗅觉学习和条件作用通常通过基于相关的联想突触可塑性来模拟。已经表明，通过电击对气味诱发反应进行条件作用取决于从肯尼恩细胞（KC）到蘑菇体输出神经元（MBON）的连接。尽管在行为水平上已经认识到条件作用是预测性的，但在电路水平上，MBON 如何形成对厌恶或喜好（效价）气味的预测仍然不清楚。我们提出了一些行为实验，这些实验不能用条件刺激和非条件刺激之间的联想可塑性很好地解释，我们提出了两种替代模型来解释预测是如何形成的。在误差驱动的预测性可塑性中，多巴胺能神经元（DAN）表示预测气味值和电击强度之间的误差。在目标驱动的预测性可塑性中，DAN 表示预测性 MBON 活动的目标。KC 到 MBON 突触的预测性可塑性也可以解释痕迹条件作用、可塑性中效价相关的符号转换以及观察到的新颖性-熟悉性表示。该模型提供了一个框架，可以剖析 MBON 电路并解释在嗅觉学习期间 DAN 活动。
