The gustatory system underlies our conscious perception of sweetness and allows us to distinguish a sweet solution from plain water. However, the neural mechanisms in gustatory cortices that enable rats to differentiate sweetness from water remain elusive. In this study, we designed a novel sucrose categorization task in which rats classified water from a gradient of sucrose solutions. We found that in the anterior Insular Cortex (aIC) and the Orbitofrontal Cortex (OFC), neural activity prioritized encoding the categorization of water versus sucrose rather than the specific concentrations within the sucrose solutions. aIC neurons more rapidly encoded sucrose/water distinction, followed by the OFC. In contrast, the OFC encoded choice information slightly earlier than aIC, but both gustatory cortices maintained a comparable encoding of the rat's choices in parallel. The encoding of sensory and categorical decisions was dynamic and sequentially encoded, with neurons carrying significant information in moving bumps at different time bins across the trial. Our results demonstrate that sucrose categorization relies on dynamic encoding sequences in the neuronal activity of aIC and the OFC rather than static, long-lasting (sustained) neural representations. Single-cell, population decoding, and principal component analyses confirmed our results. This aligns with the concept of a dynamic code, where the brain updates its representation of sucrose categorization as new information becomes available. Additionally, aIC and the OFC rapidly encoded reward outcomes. Our data supports the view that gustatory cortices use sequential and dynamic coding to compute sensorimotor transformations from taste detection to encoding categorical taste decisions and reward outcomes.

中文翻译：

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大鼠味觉皮层水-蔗糖分类的顺序和动态编码

味觉系统是我们对甜味有意识感知的基础，使我们能够区分甜味溶液和白开水。然而，味觉皮层中使大鼠区分甜味和水的神经机制仍然难以捉摸。在这项研究中，我们设计了一种新颖的蔗糖分类任务，其中大鼠对蔗糖溶液梯度中的水进行分类。我们发现，在前岛皮质（aIC）和眶额皮质（OFC）中，神经活动优先编码水与蔗糖的分类，而不是蔗糖溶液中的特定浓度。 aIC 神经元更快地编码蔗糖/水区别，其次是 OFC。相比之下，OFC 比 aIC 稍早编码选择信息，但两个味觉皮层并行地保持了大鼠选择的可比编码。感觉和分类决策的编码是动态且连续编码的，神经元在整个试验中的不同时间段的移动颠簸中携带重要信息。我们的结果表明，蔗糖分类依赖于 aIC 和 OFC 神经元活动中的动态编码序列，而不是静态、持久（持续）的神经表征。单细胞、群体解码和主成分分析证实了我们的结果。这与动态代码的概念相一致，当新信息可用时，大脑会更新其对蔗糖分类的表示。此外，aIC 和 OFC 快速编码奖励结果。我们的数据支持这样的观点：味觉皮层使用顺序和动态编码来计算从味觉检测到编码分类味觉决策和奖励结果的感觉运动转换。