““Every squirt of dopamine ends, alas, and you only get more when your brain sees another chance to approach a reward. The fleetingness of dopamine was illuminated by a recent monkey study. The animals were trained to do a task and get rewarded with spinach. After a few days, they were rewarded with squirts of juice instead of spinach. The monkeys’ dopamine soared. That seared the information: “This reeeally meets your needs” into their neurons. The experimenters continued giving the monkeys juice, and in a few days something curious happened. No dopamine spike. The monkeys’ brains stopped reacting to rewards that just came on its own. In human terms, they took it for granted. When there’s no new information, there’s no need for dopamine. When you need to record new survival rewards or new ways of getting them, your dopamine is there. This experiment has a dramatic finale. The experimenters switched back to spinach, and the monkeys reacted with fits of rage. They screamed and threw the spinach back at the researchers. They had learned to expect juice, and even though it no longer made them happy, losing it made them mad””
