Average discharge rate of Nb+/Orx+ neurons with S/Q and S/NS procedures. The discharge of all Orx neurons varied significantly as a function of the period (before, during tone, and after), the tone (Tone 1 or 2), and the training (S/Q or S/NS). A, With the S/Q procedure (n = 8 cells, 57 trials), the discharge rate of Nb+/Orx+ neurons varied significantly across periods and tones. The average discharge rate during Tone 1 was significantly higher than that during Tone 2, reflecting discrimination of auditory cues associated with appetitive versus aversive valences. B, With the S/NS procedure (n = 3 cells, 29 trials), the discharge rate also varied significantly across periods and as a function of tone. The average discharge rate was significantly higher after Tone 1 (S) than after Tone 2 (NS), reflecting learned association with the receipt of appetitive sucrose. *p < 0.05 for period and or with tone in two-way mixed RM-ANOVAs for each procedure; *p < 0.05, according to post hoc comparisons; see text.