In the Dudman Lab at HHMI's Janelia Research Campus, thirsty mice performed a simple task and were rewarded either with a few generous gulps of water or many tiny sips. The difference was dramatic: the mice given large rewards learned the task in a single day after fewer than 10 repetitions, while those receiving small rewards took many days and thousands of trials to master the same skill. This unexpected finding is forcing neuroscientists to rethink a foundational assumption they've held for decades.
For years, the field operated on a straightforward logic: learning depends on experience—the number of times you try and succeed. A poker player becomes better through volume of play, not the size of the pot. Neuroscientists applied this thinking to animal research, assuming they would need to train animals for weeks, gradually teaching them tasks through hundreds of small, incremental rewards. No one had bothered to question whether the reward's magnitude itself might accelerate learning. "The whole field has been doing it for decades and I mean this quite literally; no one ever checked," says Janelia Senior Group Leader Josh Dudman.
When the team finally tested this assumption, the results upended established doctrine. Beyond the speed of learning, something equally striking happened: the variability between individual animals collapsed. Normally, one mouse might become an expert in a week while another took a month to learn an identical task. With larger rewards, all the animals learned in a few days, moving together through the learning curve. "But instead, now in a day, I'm watching these mice just nail it," says Luke Coddington, the senior scientist who led the study.
The mechanism behind this acceleration lies in dopamine, a chemical messenger in the brain that regulates learning and motivation. The researchers discovered that larger rewards triggered more substantial dopamine releases—but crucially, these signals lasted longer. When the team artificially extended dopamine signals associated with small rewards, they found learning also accelerated. This sustained dopamine signal altered three key components of learning: how much the animals absorbed from each repetition, how well they retained knowledge between sessions, and critically, how engaged they remained throughout training.
Coddington describes the shift in vivid terms: "We think that when we make dopamine responses way bigger in these experiments, we're turning all the 'kids' in our 'classroom' into really engaged students." That engagement—the sustained attention and motivation that comes from bigger rewards—emerged as the strongest predictor of individual variation in learning speed. Animals weren't just learning faster; they were learning while fully present.
The implications reach far beyond understanding mouse behavior. This discovery is already reshaping how neuroscience labs conduct research. By dramatically reducing training time and eliminating the variability that makes learning difficult to study, larger rewards make the learning process itself a clearer experimental subject. The Dudman Lab has reorganized their work around these findings. "It changed how, more or less, all of our current projects are done now," Dudman notes. Moreover, the ability to train animals more quickly suggests mice could master far more complex tasks than previously thought possible, opening new avenues for studying learning and cognition that seemed out of reach before. The research, published in the journal Science, signals a shift in how neuroscientists will approach skill training—one where the size of the reward is no longer an afterthought but a central lever in understanding how brains learn.