Computational Systems Neuroscience, Institute of Zoology, University of Cologne, Zülpicher Str. 47b, 50674 Cologne, Germany.
Computational Systems Neuroscience, Institute of Zoology, University of Cologne, Zülpicher Str. 47b, 50674 Cologne, Germany.
Curr Biol. 2023 Oct 9;33(19):4217-4224.e4. doi: 10.1016/j.cub.2023.08.016. Epub 2023 Aug 31.
Animals form a behavioral decision by evaluating sensory evidence on the background of past experiences and the momentary motivational state. In insects, we still lack understanding of how and at which stage of the recurrent sensory-motor pathway behavioral decisions are formed. The mushroom body (MB), a central brain structure in insects and crustaceans, integrates sensory input of different modalities with the internal state, the behavioral state, and external sensory context through a large number of recurrent, mostly neuromodulatory inputs, implicating a functional role for MBs in state-dependent sensory-motor transformation. A number of classical conditioning studies in honeybees and fruit flies have provided accumulated evidence that at its output, the MB encodes the valence of a sensory stimulus with respect to its behavioral relevance. Recent work has extended this notion of valence encoding to the context of innate behaviors. Here, we co-analyzed a defined feeding behavior and simultaneous extracellular single-unit recordings from MB output neurons (MBONs) in the cockroach in response to timed sensory stimulation with odors. We show that clear neuronal responses occurred almost exclusively during behaviorally responded trials. Early MBON responses to the sensory stimulus preceded the feeding behavior and predicted its occurrence or non-occurrence from the single-trial population activity. Our results therefore suggest that at its output, the MB does not merely encode sensory stimulus valence. We hypothesize instead that the MB output represents an integrated signal of internal state, momentary environmental conditions, and experience-dependent memory to encode a behavioral decision.
动物通过评估背景经验和当前动机状态下的感官证据来做出行为决策。在昆虫中，我们仍然缺乏关于行为决策是如何形成以及在感觉运动回路的哪个阶段形成的理解。蘑菇体（MB），昆虫和甲壳类动物的中枢脑结构，通过大量的反复出现的、主要是神经调制的输入，将不同模态的感觉输入与内部状态、行为状态和外部感觉环境整合在一起，这暗示了 MB 在状态依赖的感觉运动转换中具有功能作用。在蜜蜂和果蝇中的许多经典条件反射研究已经提供了积累的证据，表明在其输出端，MB 对与行为相关性有关的感觉刺激进行了效价编码。最近的工作已经将这种效价编码的概念扩展到先天行为的背景中。在这里，我们共同分析了蟑螂的一种特定进食行为和同时从 MB 输出神经元（MBONs）进行的细胞外单细胞记录，以响应定时的感觉刺激与气味。我们发现，清晰的神经元反应几乎只在行为反应的试验中发生。MBON 对感觉刺激的早期反应先于进食行为，并从单试群体活动中预测其发生或不发生。因此，我们的结果表明，在其输出端，MB 不仅仅编码感觉刺激的效价。相反，我们假设 MB 输出代表内部状态、当前环境条件和经验依赖性记忆的综合信号，以编码行为决策。
