Summary: A new Columbia University study finds that overnight the brain selectively preserves memories tied to rewarding events while allowing less relevant details to fade. These findings reveal how memory consolidation helps shape future decisions and behavior.
Source: Columbia University
How does the brain decide which experiences to keep and which to discard? New research shows that reward plays a central role in shaping which memories are consolidated for future use.
Researchers at Columbia University report that the brain automatically replays and strengthens memories for events associated with reward, while neutral or inconsequential details are gradually filtered out. Published in Nature Communications, the study sheds light on memory consolidation, reward processing, and the ways memory supports decision making.
“Memory is not a perfect record of experience,” said Daphna Shohamy, senior author and principal investigator at Columbia’s Mortimer B. Zuckerman Mind Brain Behavior Institute and a professor of psychology. “We cannot store everything, so the brain prioritizes information that will be most useful later.”
The researchers found that this prioritization is not immediate. “The strengthening of memories tied to reward takes time,” said Erin Kendall Braun, a co-author and recent graduate student in the Shohamy lab. “Our results indicate that both a brief window after receiving a reward and an extended overnight period, likely including sleep, work together to reorganize which events are remembered.”
To test these ideas, participants explored computer-simulated mazes in search of a hidden gold coin worth one dollar. As they navigated the grid-like mazes, images of ordinary objects—such as an umbrella or a mug—appeared at different locations. Later, without prior warning, participants were given a memory test for those objects.
When the surprise memory test occurred 24 hours after exploration, participants were more likely to recall the objects that had appeared closest in time and space to the reward—the moment they found the coin—while objects farther from the reward tended to be forgotten. This indicates a retroactive effect of reward: items that were neutral at the time of encoding became more memorable because they were associated with a subsequent reward. Notably, the same pattern did not appear in tests given immediately after exploration, suggesting that consolidation processes unfolding over hours, including overnight sleep, were necessary for reward-driven memory prioritization.
The finding was robust: the experiment was replicated in six variations with a combined total of 174 participants.
“Many of the experiences we encounter seem mundane when they happen, yet our memories for them can be reshaped later if they become meaningful,” Shohamy said. “These results show that memory retention is systematic rather than random: the brain automatically preserves experiences that matter for future behavior.”
The study suggests a likely role for dopamine—an important neurotransmitter in reward signaling—and the hippocampus, the brain region essential for long-term memory. However, the precise neural circuit mechanisms that implement retroactive, graded prioritization remain unknown and will require further research.
Shohamy noted that a logical next step would be to study how negative or aversive events influence memory consolidation, although such experiments present ethical and practical challenges. Understanding how motivation, whether positive or negative, shapes memory could have implications for education, behavior change, and mental health interventions.
Funding: The research was supported by the National Institutes of Health (grant 5R01DA038891 to D.S.), the McKnight Foundation (MCKNGT CU16-0460 to D.S.), and the National Science Foundation (Career Award BCS-0955494 to D.S. and Graduate Research Fellowship DGE-1144155 to E.K.B.).
Source: Carla Cantor, Columbia University
Publisher: Organized by NeuroscienceNews.com
Image source: NeuroscienceNews.com (public domain)
Original research: Braun, E. K., Wimmer, G. E., & Shohamy, D. “Retroactive and graded prioritization of memory by reward,” Nature Communications, published November 20, 2018. doi: 10.1038/s41467-018-07280-0
Retroactive and graded prioritization of memory by reward
Decisions often rely on an internal model built from past experience, but how that model is constructed and stored in memory is not fully understood. This study tested whether reward retroactively prioritizes memory for items encountered along sequences of events. Human participants encountered neutral objects while exploring mazes for reward. Across six data sets, reward systematically modulated memory for neutral objects, retroactively strengthening memory for objects nearest the reward. This effect emerged only after a 24-hour delay and was stronger for sequences followed by a longer rest interval, consistent with a role for post-reward replay and overnight consolidation as observed in animal studies. These findings indicate that reward retroactively prioritizes memory along a temporal gradient, supporting adaptive decision-making.
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