From addiction to everyday decision-making, impulsivity shapes much of our behavior. A new study reveals how dopamine, reward size, and learned expectations combine to push us toward premature actions—even when we know better. By showing that impulsivity rises with the value of anticipated rewards, the research offers a new framework for understanding why we sometimes sabotage our own best interests.

[Hebrew University of Jerusalem]– Why do we sometimes act impulsively even when we know it will cost us? A study led by Prof. Eran Lottem from the Edmond and Lily Safra Center for Brain Sciences (ELSC) at the Hebrew University of Jerusalem offers an illuminating answer: impulsivity is a predictable consequence of how our brains process value.

Published in the journal Biological Psychiatry, the study reveals that the more valuable a reward is perceived to be, the harder it becomes to resist the temptation to act prematurely, even when waiting would lead to a better outcome. This paradoxical finding suggests that impulsive behavior can be understood as a form of Pavlovian bias, where anticipated rewards automatically trigger action—even when that action is inappropriate.

To explore this phenomenon, Prof. Lottem and Hebrew University colleagues—including Zhe Liu, Robert Reiner, and Prof. Yonatan Loewenstein—designed an experiment in which subjects were trained to perform a waiting task. Participants had to delay their responses in order to receive water rewards of varying sizes. The team found that premature actions were significantly more likely when larger rewards were at stake.

The team developed a computational model of reinforcement learning that integrated Pavlovian bias to explain this behavior. They also used fiber photometry to monitor dopamine release in the ventral striatum, a brain region involved in value learning and decision-making, and optogenetic stimulation to manipulate dopamine signals directly. Their findings confirmed that dopamine activity both predicted and influenced the animals’ impulsivity—with larger expected rewards driving greater temptation to act.

“Our results show that impulsive behavior isn’t necessarily irrational—it’s often tied to how we’ve learned to value outcomes over time,” said Prof. Lottem. “The brain’s reward system can push us to act before we think, especially when high-value rewards are involved.”

These insights may have broader implications for understanding impulse-control disorders such as ADHD, gambling, and addiction. By linking impulsivity to reward valuation and dopamine dynamics, the study offers a new framework for studying—and potentially treating—self-defeating behavior.