a–c, Putative GABA neurons in the dopamine identification experiment (Fig. 1). d–f, Putative GABA neurons in the GABA stimulation experiment (Fig. 2). a, b, Average firing rate of putative GABA neurons to unexpected (a) or expected (b) rewards of various sizes. c, Population responses (mean ± s.e.m. across putative GABA neurons) for different reward sizes. Orange, unexpected reward. Black, expected reward. Responses were averaged over a 600 ms window after reward delivery. d, e, Average firing rate of putative GABA neurons to rewards of various sizes, delivered with (e) or without (d) optogenetic GABA stimulation. f, Population responses (mean ± s.e.m. across putative GABA neurons) for different reward sizes. Blue, reward with laser stimulation. Black, reward without laser stimulation. Responses were averaged over a 600 ms window after reward delivery.