Fig. 2. MS GABAergic neurons encode reward signals.

a Optrode recording from MS GABAergic neurons while sucrose water (5% w/v) was delivered and animal licked. Upper right, LED pulses (at 16 Hz, blue dots) evoked spikes in an example tagged GABAergic neuron and an untagged neuron. Lower left, average spike waveforms for LED-evoked (blue) and sucrose-evoked (red) spikes in the same tagged units. Note that the waveforms are slightly offset for comparison. Scale bar, 0.5 ms. Lower right, raster (upper) and peri-stimulus spike time histogram (PSTH, lower) plots of spikes of the example neurons. Shaded blue indicates the duration of the LED pulse. b Heatmap plot of Z-score for all recorded tagged GABAergic units (ChR2+, n = 75), and untagged units (ChR2−, n = 94). They were ranked and divided into three subgroups: excitatory response, no response, suppressive response. c Proportion of cells in each subgroup for tagged and untagged populations, ****p < 0.0001, κ² Test, two-sided. d Percentages of tagged and untagged neurons in the recorded population activated by sucrose. e, f Heatmap plot of peri-stimulus Z-score (upper) for all the recorded MS Vglut2+ units (n = 19) and the corresponding population average (lower) in response to sucrose (e) or 5 mM quinine (f) passively received. Gray shade indicates s.e.m. g Comparison of the mean Z-score within a 0–2 s window after the onset of licking per se (without liquid delivered, n = 7), or in response to sucrose or quinine for Vgat+ neurons (n = 75 and 11, respectively) and to sucrose/quinine for Vglut2+ neurons (n = 19). ****p < 0.0001, one-way ANOVA with post-hoc Tukey’s test, two-sided. h Population average of peri-stimulus Z-score for Vgat+ neurons (n = 11) in response to sucrose of different volumes (3 µL, 6 µL, or 10 µL). Gray shade indicates s.e.m. i Mean Z-score plotted against sucrose volume, n = 11 cells. Dark red solid line shows the best-fit linear regression line. Dashed lines, 95% confidence intervals. Source data are provided as a Source Data file.