Brief-access rigs and experimental timeline.

(A) The brief-access rig—multiple bottles, each made available periodically. To the right are example data schematizing the analysis of rhythmic licking to pull out lick numbers and “clusters,” both of which reflect palatability. (B) The experimental timeline, showing preference testing sessions and the delay (for surgery and recovery) between the final BAT day and Electrophysiology recording/passive tastant deliveries.

Passive taste delivery and electrophysiology recording and histological verification.

(A) A schematic of in vivo GC recordings with taste delivery via a pre-implanted intra-oral cannula. (B) Histological verification of a representative electrode implant site (left) with dye marking the recording site in gustatory cortex. On the right is the schematic of the coronal slice through central GC, with the positions of electrode tips for all animals (N=9) denoted with red circles.

Individual and between-session differences in perceived taste palatability.

(A1) Mean lick cluster sizes for two representative rats during the first BAT test illustrate clear individual differences in preference for sucrose, NaCl, and QHCl. A two-way ANOVA revealed a significant Taste × Animal interaction (F(2,65) = 13.44, p < 0.05). Post hoc Tukey tests further showed that sucrose, while highly preferred by the rat on the left, was perceived similarly to QHCl by the rat on the right (p < 0.05). (A2) Mean lick cluster sizes for each taste across all animals during the first BAT test (N = 9). The two rats shown in panel (A1) are outlined for reference. (A3) Differences in lick cluster sizes comparing sucrose and NaCl (top) and comparing citric acid (CA) and quinine (QHCl; bottom) during the first BAT test. One-sample t-tests (against a population mean of zero) revealed individual differences in the preferences for the two palatable and the two aversive tastes (p < 0.05). (B1-3) The same analyses as in A1-3, but for each rat’s final BAT session (depending on the rat, sessions 3 or 5). In (B3), we also show an analysis of whether individual rats changed their relative preferences between BAT sessions—two-way ANOVAs with variables Animal and Session, comparing the data shown in panels (A3) and (B3). The majority of rats exhibited significant changes in relative preference for tastes of the same valence across sessions (# ps < 0.05). The labels R1–R9 denote the rats included in the data analysis.

Palatability-relatedness of Late-epoch taste responses match the individuals’ preferences.

(A) Peristimulus time histogram of 4 passively delivered tastes for a representative cortical neuron, showing typical response dynamics including correlation (r-squared, dotted line and right y-axis) to palatability peaking around 1 second from taste delivery. (B) Palatability correlations from the GC unit (A) calculated based on the canonical ranking or the ranks estimated from either first or final BAT test. Inset: Bar plot showing the average lick cluster sizes for each taste obtained during the final BAT testing session. Concentrations for each taste were as follows: QHCl, 7.8 × 10⁻⁵ M; CA (Citric Acid), 0.009 M; NaCl(L), 0.05 M; and NaCl, 0.1 M.

The correlation between Late-Epoch GC firing and an individual rat’s taste preferences is specific to the most recent BAT assay.

(A). The palatability correlation over time from all of the (n=129) recorded neurons, using canonical palatability (green), lick cluster data from the first BAT session (blue), and lick cluster data from the final BAT session (orange). (B) The difference in correlation calculated from canonical palatability and data from the animal’s individual preferences (First BAT or Final BAT), separated into the Identity epoch (200-7000ms) and the Palatability epoch (700-1200ms). * p < 0.01, *** < 0.001.

A single session of IOC taste delivery to passive rats nullifies the correlation with palatability calculated from the most recent BAT assay.

(A) Cortical coding no longer matches rats’ individual preferences when using neurons (n=101) from electrophysiology session 2 (same conventions used in Figure 5A. (B) A summary of the data in (A), showing there is no longer a significant difference using preference rankings estimated from BAT performance.

Summary of taste stimuli used in brief-access tests (BATs) and electrophysiological recording sessions.

QHCl: quinine hydrochloride.