Figure 1. Experimental paradigm.

(A) 4–6 weeks after receiving surgeries for virus injections, rats were implanted with opto-trodes and EMG electrodes. Post recovery, they were given intra-oral infusions of Dil Suc (30mM Sucrose), Conc Suc (300mM Sucrose), Dil Qui (0.1mM Quinine-HCl) and Conc Qui (1mM Quinine-HCl), and ArchT-expressing GC neurons were briefly inhibited by green (532 nm) laser light. (B) Coronal slice from a subject, showing ArchT expression (visualized by the GFP tag) localized in gustatory cortex (GC). A small lesion, left by the tip of the opto-trode is visible in the middle of the GFP expressing region, and had no general impact on behavior (see below). (C) Inhibition protocol used in the study: two types of optogenetic perturbations, short (0.5s) or long (2.5s), were delivered in separate experimental sessions. Short perturbations were delivered at one of three possible time points on any individual trial, and are referenced as follows in the text: (1) 0–0.5s - early 0.5s perturbations, (2) 0.7–1.2s - middle 0.5s perturbations, and (3) 1.4–1.9s - late 0.5s perturbations. Not shown, but delivered in all sessions, were control trials with no perturbations. Grey dashed lines mark the approximate range of the ensemble transitions to palatability/decision-related firing. (D) A schematic of the temporal structure of single-neuron coding across the first 2.0s of taste responses in GC. Immediately following taste presentation, responses are nonspecific, indicating only the presence of fluid on the tongue (‘detection’ epoch, in teal). The next two temporal epochs of GC firing are taste specific: the first codes the physio-chemical identity of the stimulus (‘identity’ epoch, in orange); following a transition (that can happen anywhere between 0.5–1.5s post stimulus on individual trials, see grey dashed lines, and on average happens midway through this period) firing rates change to reflect palatability and the upcoming consumption decision (‘palatability’ epoch, in pink).