Real-time place preference test

We placed individual mice in a custom-made behavioral arena (50 × 50 × 30 cm white plastic chamber) for 15 min per session. The wall between the left and the right chamber was half-open for the freely behaving of mouse connected with optical patch cable. We conducted baseline and stimulation sessions, and examined the effect of stimulation or inhibition of NI NMB neurons. In the activation experiments, animals that entered the optogenetic-stimulation chamber received blue laser pulses (5 ms per pulse at the frequencies of 50 Hz, 20 mW, 470 nm). We used 5 s on/5 s off laser stimulation protocol to avoid continuous running so that the mouse cannot cross back into the non-stimulation side, that might cause false-positive reward phenotype. In the inhibition experiments, the mice received constant blue laser (4 mW, 470 nm) until they crossed back into the non-stimulation side. The locations of the mouse were assessed from the video recording data using a custom MATLAB program.