Neuronal Sequences and dynamic coding of water-sucrose categorization in rat gustatory cortices

The gustatory system allows us to perceive and distinguish sweetness from water. We studied this phenomenon by recording neural activity in rats' anterior insular (aIC) and orbitofrontal (OFC) cortices while they categorized varying sucrose concentrations against water. Neurons in both aIC and OFC encoded the categorical distinction between sucrose and water rather than specific sucrose concentrations. Notably, aIC encoded this distinction faster than OFC. Conversely, the OFC slightly preceded the aIC in representing choice information, although both cortices encoded the rat's choices in parallel. Further analyses revealed dynamic and sequential encoding of sensory and categorical decisions, forming brief sequences of encoding neurons throughout the trial rather than long-lasting neuronal representations. Our findings, supported by single-cell, population decoding, and principal-component analysis (PCA), demonstrate that gustatory cortices employ neuronal sequences to compute sensorimotor transformations, from taste detection to categorical decisions, and continuously update this process as new taste information emerges using dynamic coding.