Fig. 6: SOM but not PV MS neurons encode reward signals.

a Spikes of an example SOM (top) and PV (bottom) MS neuron to pulses of LED light (blue dot) in optrode recording. Right inset, comparison of spike waveforms evoked by LED (blue) and sucrose (red). b Top, heatmap plot of peri-stimulus Z-score for responses of SOM neuron to sucrose. 19/22 units showed significant excitatory responses while 3/22 units did not show significant responses (divided by the white horizontal line). Bottom, population average of Z-score for neurons showing excitatory (red) or no (black) responses. c PV neuron responses to sucrose. 3/23 units showed significant inhibitory responses while 20/23 units did not show significant responses. d Proportion of responsive versus non-responsive neurons in SOM and PV groups. e Mean Z-score value for all the recorded SOM (n = 22) and PV (n = 23) neurons. ****p < 0.0001, two-sided t test. All error bars in this figure indicate s.d. f Fiber photometry recording setup. GCaMP6s was expressed in SOM neurons. g Average calcium signals in response to sucrose (red) or water only (black) (2 animals, 25 trials in each animal). Shades indicate s.e.m. h Top, slice recording from tdTomato-labeled MS SOM neurons while photo-stimulating axon terminals from ChR2-expressing PBN neurons. Bottom, LED-evoked EPSC recorded under -70mV holding potential in an example MS SOM neuron, in the presence of TTX and 4AP. Scale bar, 10 pA, 25 ms. i Average EPSC amplitudes of 8 out of 19 MS SOM neurons evoked by LED stimulation of PBN axons. Error bars represent s.d. j Optogenetic activation of SOM or PV neurons in MS in behaving mice. k Movement tracks for an example animal in RTPP test with photoactivation of SOM neurons. l Percentage time spent in the LED-On chamber for GFP control and ChR2-expressing groups. ***p = 0.0002, two-sided t test, n = 10 mice in each group. m, n RTPP test with photoactivation of PV neurons. **p = 0.001, two-sided t test, n = 10 mice in each group. Source data are provided as a Source Data file.