Neural representations of reward-related memories shift across development

Rewards signal information in the environment that is valuable and thus useful to remember. Rewards benefit memory across development, but how reward-associated memories are represented in the brain has not been well characterized. Here we conducted pattern similarity analyses of fMRI data in male and female participants aged 8-25 to elucidate how neural representations in key memory-related brain areas are influenced by reward, and how these relationships change across childhood and adolescence. We found that reward information was reflected in pattern similarity during encoding in ventral temporal cortex and in changes in similarity from encoding to retrieval in anterior hippocampus (aHC). Strikingly, aHC reward-sensitive representations also varied with age such that adults' memory benefitted from stability of hippocampal representations, whereas younger participants' memory improvements were associated with greater drift in representations over time. Moreover, across all participants, reward-related univariate activation in the ventral tegmental area was associated with a greater tendency toward representational drift in aHC. Taken together, our findings demonstrate that reward modulates neural memory representations, and that the representational patterns supporting reward-motivated memory shift with age.Significance statement Rewards benefit memory across development, but how these memories are represented in the brain has not been well characterized. Here we looked at multivariate patterns of brain activity in children, adolescents, and adults and found that the reward level (high versus low) assigned to pairs of pictures influenced participants' neural patterns both during learning and when they retrieved the pairs from memory. Strikingly, in the hippocampus, adults' memory for high-reward pairs benefitted from pattern stability over time, while children and adolescents' high-reward memory benefits were associated with greater change in hippocampal patterns from encoding to retrieval. These results demonstrate that neural representations of reward-associated memories change with age across development.