Reconstructing dopamine's link to reward (2024)

Summary

“It’s a more realistic way of thinking about the anatomy,” says Ilana Witten, professor of neuroscience at Princeton University, who led the 2019 study and co-authored the new paper with Daw. The team’s feature-specific model also makes sense in terms of how the brain might solve the complicated problem of learning in a multi-modal environment, Witten says. “It can just make the problem less complicated to predict reward based on any one modality” for certain dopamine projections, she says. “It’s a lower-dimensional problem.” Researchers had already tweaked the RPE model to better fit a series of observations about the dynamics of dopamine activity. Once experiments moved from classical conditioning, as in the original monkey study, to rodents navigating virtual environments, researchers began seeing an unusual ramping up of dopamine signals as the animals approached a reward, as first reported in a 2013 paper. These “ramps” are more consistent with dopamine signaling a reward’s value than they are with it signaling errors in reward prediction, others proposed in the years after. But later work directly contradicted that idea and found that the classic RPE model could, with appropriate adjustments, account for those ramps. “It’s not a disqualifying feature of the prediction model,” says Samuel Gershman, professor of psychology at Harvard University, who conducted that work. After accounting for ramps and considering the ways in which prediction errors can generalize, the theory remains a useful way to account for dopamine’s role, Gershman and his colleagues argue in the recent perspective article. Daw and his colleagues have a similar view when it comes to the traditional RPE model: “I wouldn’t say we’re apologists for it,” Daw says. “But we’re trying to preserve what’s good about it, and sort of extend it.” T his series of RPE rewrites has not assuaged a litany of concerns that other teams have raised, including the model’s flexibility. “There’s a danger that [RPE]...