小柯机器人

美国加州大学圣迭戈分校Ralph J. Greenspan研究小组揭示果蝇痕迹和延迟条件反射的不同机制。这一研究成果于2022年2月16日在线发表在国际学术期刊《自然》上。

研究人员表示，在人类和高阶哺乳动物中，两种形式的联想学习（延迟条件反射和痕迹条件反射），已被广泛研究。在延迟条件反射中，非条件刺激（例如电击）是在条件刺激（例如音）的最后时刻引入的，两者同时结束。在痕迹条件反射中，条件刺激和非条件刺激之间有一个"痕迹"间隔。因此，痕迹条件反射依赖于在条件刺激终止后保持对其的神经表征（从而使分心成为可能），以学习条件刺激-非条件刺激的偶然性；这使得它比延迟条件反射在认知上要求更高。

通过将虚拟现实行为与神经遗传学操作和体内双光子脑成像相结合，研究人员表明果蝇的视觉痕迹条件反射和延迟条件反射会调动椭球中的R2和R4m环状神经元。在痕迹条件反射中，痕迹间隔期间的钙瞬态表现为振荡增加，并在反复训练中缓慢下降，而且这两种效应对分心敏感。多巴胺能活动伴随着环状神经元的信号持续性，这一点仅在痕迹条件反射期间因分心而减少。

最后，多巴胺D1样和D2样受体在环状神经元中的信号传导在延迟和痕迹条件反射中具有不同的作用；多巴胺D1样受体1介导两种形式的调节，而多巴胺D2样受体只参与在痕迹条件反射的痕迹区间维持环状神经元的活动。这些观察结果与先前报道的哺乳动物在唤醒、前额叶激活和高水平认知学习期间的观察结果相似。

附：英文原文

Title: Differential mechanisms underlie trace and delay conditioning in Drosophila

Author: Grover, Dhruv, Chen, Jen-Yung, Xie, Jiayun, Li, Jinfang, Changeux, Jean-Pierre, Greenspan, Ralph J.

Issue&Volume: 2022-02-16

Abstract: Two forms of associative learning—delay conditioning and trace conditioning—have been widely investigated in humans and higher-order mammals1. In delay conditioning, an unconditioned stimulus (for example, an electric shock) is introduced in the final moments of a conditioned stimulus (for example, a tone), with both ending at the same time. In trace conditioning, a ‘trace’ interval separates the conditioned stimulus and the unconditioned stimulus. Trace conditioning therefore relies on maintaining a neural representation of the conditioned stimulus after its termination (hence making distraction possible2), to learn the conditioned stimulus–unconditioned stimulus contingency3; this makes it more cognitively demanding than delay conditioning4. Here, by combining virtual-reality behaviour with neurogenetic manipulations and in vivo two-photon brain imaging, we show that visual trace conditioning and delay conditioning in Drosophila mobilize R2 and R4m ring neurons in the ellipsoid body. In trace conditioning, calcium transients during the trace interval show increased oscillations and slower declines over repeated training, and both of these effects are sensitive to distractions. Dopaminergic activity accompanies signal persistence in ring neurons, and this is decreased by distractions solely during trace conditioning. Finally, dopamine D1-like and D2-like receptor signalling in ring neurons have different roles in delay and trace conditioning; dopamine D1-like receptor 1 mediates both forms of conditioning, whereas the dopamine D2-like receptor is involved exclusively in sustaining ring neuron activity during the trace interval of trace conditioning. These observations are similar to those previously reported in mammals during arousal5, prefrontal activation6 and high-level cognitive learning7,8.

DOI: 10.1038/s41586-022-04433-6

Source: https://www.nature.com/articles/s41586-022-04433-6

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