Fig. 2: Similar within-neuron dopamine firing responses to sucrose and remifentanil predictive cues.

a Dopamine neuron identification (N = 11 rats). (i) Heatmap showing functional activation of each unit (rows) aligned to sucrose cue onset (0 s). Activity normalized using area under receiver-operator curve (auROC) method, compared against baseline. Scales from 0 to 1. (ii) First three components extracted via principal component analysis. (iii) Dendrogram showing results from hierarchical clustering. (iv) Mean auROC for units classified into each cluster. (v) PSTH and raster plots from example units for each cluster. b Example responses from a single unit to sucrose (blue, top), remifentanil (green, middle), and neutral (red, bottom) cues. Red and blue shaded regions indicate distinct phases of cue response reflecting detection (30–180 ms) and valuation (180–500 ms). Inset waveform represents mean of sorted unit. Scale bars: 50 μV and 500 ms. c PSTH traces showing average dopamine firing during sucrose (blue, 40 μL), remifentanil (green, 4 μg/kg), and neutral trials (red). All traces show mean ± SEM. d Mean baseline-subtracted firing rates during cue response to sucrose, RMF, and neutral cues (Friedman test, F = 31.71, n = 21, p < 0.0001, with Dunn’s multiple comparison test: sucrose vs. remifentanil p > 0.9999, sucrose vs. neutral p < 0.0001, remifentanil vs. neutral, p < 0.0001). All bars show mean + SEM. e Close-up of cue period from Fig. 2c. f Scatter plot of individual units’ responses to sucrose (abscissa) and RMF (remifentanil; ordinate) cues during the detection phase. Inset: cue responses during the detection phase (Friedman test, F = 16.29, n = 21, p = 0.0003, with Dunn’s multiple comparison test: sucrose vs. remifentanil p > 0.9999, sucrose vs. neutral p = 0.0006, remifentanil vs. neutral, p = 0.0036). g Individual units’ responses during the evaluation phase presented as in Fig. 2f. Note that identical Chi-squared statistics to 2 f are due to equal numbers of units exhibiting firing to remifentanil > sucrose in both intervals. Inset: cue responses during the evaluation phase Friedman test, F = 28.67, n = 21, p < 0.0001, with Dunn’s multiple comparison test: sucrose vs. remifentanil p > 0.9999, sucrose vs. neutral p < 0.0001, remifentanil vs. neutral, p < 0.0001). Source data are provided as a Source Data file.