The study investigates the distinct roles of direct and indirect pathway striatal neurons in reinforcement learning. By optogenetically activating D1- or D2-receptor-expressing striatal projection neurons in mice, the researchers found that stimulating D1-expressing neurons (dMSNs) induced persistent reinforcement, while stimulating D2-expressing neurons (iMSNs) induced transient punishment. This suggests that activation of these circuits is sufficient to modify the probability of performing future actions. The findings highlight the importance of understanding the specific roles of these neurons in reinforcement and punishment, which are fundamental processes that shape animal learning and are implicated in various psychiatric disorders. The study also demonstrates that the level of dMSN activation correlates with the magnitude of reinforcement, and that dopamine signaling is not necessary for the acquisition of trigger preference, as DA antagonists did not impair the learning process. These results provide insights into the neural substrates of reinforcement and punishment, which could inform future therapeutic approaches for psychiatric disorders.The study investigates the distinct roles of direct and indirect pathway striatal neurons in reinforcement learning. By optogenetically activating D1- or D2-receptor-expressing striatal projection neurons in mice, the researchers found that stimulating D1-expressing neurons (dMSNs) induced persistent reinforcement, while stimulating D2-expressing neurons (iMSNs) induced transient punishment. This suggests that activation of these circuits is sufficient to modify the probability of performing future actions. The findings highlight the importance of understanding the specific roles of these neurons in reinforcement and punishment, which are fundamental processes that shape animal learning and are implicated in various psychiatric disorders. The study also demonstrates that the level of dMSN activation correlates with the magnitude of reinforcement, and that dopamine signaling is not necessary for the acquisition of trigger preference, as DA antagonists did not impair the learning process. These results provide insights into the neural substrates of reinforcement and punishment, which could inform future therapeutic approaches for psychiatric disorders.