Dat tta

20 both female and male mice, 2–14 months old were used in this study. We used heterozygote for DAT-Cre (Slc6a3^{tm1.1(cre)Bkmn}; The Jackson Laboratory, 006660)⁴⁹ , DAT-tTA (Tg(Slc6a3-tTA)2Kftnk; this study), VGluT3-Cre (Slc17a8^{tm1.1(cre)Hze}; The Jackson Laboratory, 028534)^{50 (link)}, LSL-tdTomato (Gt(ROSA)26Sor^{tm14(CAG-tdTomato)Hze}; The Jackson Laboratory, 007914)^{51 (link)}, and Ai148D (B6.Cg-Igs7^{tm148.1(tetO-GCaMP6f, CAG-tTA2)Hze}/J; The Jackson Laboratory, 030328)^{52 (link)} transgenic lines. VGluT3-Cre lines crossed with LSL-tdTomato were used for experiments with DA sensor, without use of Cre recombinase. Seven mice (5 males and 2 females) were used for first-time learning, twelve mice (9 males and 3 females) were used for reversal learning, and five mice (4 males and 1 females) were used for repeated learning. Mice are housed on a 12 hr dark (7:00–19:00)/12 hr light (19:00–7:00) cycle. Experiments were performed in the dark period. Ambient temperature is kept at 75±5 F° and humidity is kept below 50%. All procedures were performed in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals and approved by the Harvard Animal Care and Use Committee