Incorporation of possible secondary effects of DA depletion into the model. Incorporation of possible secondary effects of DA depletion into the model. A, A circuit mechanism of TD-RPE calculation in DA neurons that has been suggested, in which DA neurons receive input representing the obtained reward from a subpopulation of the PPN neurons. VTA, ventral tegmental area; SNc, substantia nigra pars compacta; NAc, nucleus accumbens. B, Schematic diagram of the secondary effect that we incorporated into the model. The PPN neuronal activity representing the obtained reward was assumed to gradually increase after DA depletion. C, Assumed gradual increase in the gain of the obtained-reward-representing input to DA neurons, corresponding to the coefficient (C) of the obtained-reward term in the formula of TD-RPE as shown in the bottom. The solid and dashed lines indicate the gain increase up to twice and three times of the original assumed in the simulations in Figs. 5 and 6 and Fig. 8, respectively. Kenji Morita, and Ayaka Kato eNeuro 2018;5:ENEURO.0021-18.2018 ©2018 by Society for Neuroscience