Motivated behavior unfolds across multiple timescales, requiring animals to balanceengagement with a current reward against preparation for the next reward opportunity.
　Although midbrain dopamine neurons are central to motivated behavior, how these distinct　motivational components are coordinated within the dopamine system remains unclear. In this　seminar, I will present our recent work using a self-paced, multi-step decision-making task　in freely moving rats, combined with pathway- and cell-type-specific optogenetic　identification and dense electrophysiological recordings. We tested whether dopamine neurons associated with current reward engagement and future-oriented trial initiation form distinct subpopulations, and whether these subpopulations differ in their within-trial temporal response patterns. We identified two dopamine neuron subpopulations with distinct projection biases, reward-related dynamics, and behavioral correlates. One subpopulation, biased toward ventromedial striatal projections, showed gradual, seconds-scale increases in activity during reward approach and was 　referentially associated with future-oriented trial initiation. In contrast, the other, biased toward ventrolateral striatal projections, showed declining approach activity followed by a sharp pre-reward increase and sustained post-reward activity, and was preferentially associated with current reward engagement.
　Their relative dominance shifted across behavioral transition points within single trials, as behavior moved from current reward engagement toward preparation for the next reward opportunity. These findings suggest that distinct dopamine neuron subpopulations are dynamically reweighted across motivational components within single trials, raising the possibility that they contribute to motivation over different temporal horizons.