Novelty and uncertainty regulate the balance between exploration and exploitation through distinct mechanisms in the human brain.

Both novelty and uncertainty are potent features guiding exploration; however, they are often experimentally conflated, and an understanding of how they interact to regulate the balance between exploration and exploitation has proved elusive. Using a task designed to decouple the influence of novelty and uncertainty, we identify separable mechanisms through which exploration is directed. We show that uncertainty-directed exploration is sensitive to the prospective benefit offered by new information, whereas novelty-directed exploration is maintained regardless of its potential advantage. Using a computational framework in conjunction with fMRI, we show that uncertainty-directed choice is rooted in an adaptive bias indexing the prospective utility of exploration. In contrast, novelty persistently promotes exploration by optimistically inflating reward expectations while simultaneously dampening uncertainty signals. Our results identify separable neural substrates charged with balancing the explore/exploit trade-off to foster a manageable decomposition of an otherwise intractable problem.