NOV 26, 2018 10:20 PM PST

Most Rewarding Experiences Take The Top Spot In Memory

Prioritizing the daily to-do list to maximize productivity is something that is suggested to be successful. One classic way of prioritizing is analyzing the reward of what is to be done to the risk associated with it. Our brain follows the same principle as well to prioritize which memories get stored. The most significant memories like your birthday, graduation, wedding among others get stored and flowers you saw passing by on your drive, a restaurant menu gets the least preferred. This sorting allows for decluttering and remembering the most important things.

Research done by the Columbia University researchers published on the Nov. 20 in the journal Nature Communications shows that brain filters out neutral, inconsequential events, retaining only the memories that are useful to future decisions. Not only is the rewarding moment stored, but also the events leading up to the reward are stored, and this allows for memory shaped decision making. Sometimes we could anticipate the reward and before the onset of the reward, beneficial effects might be seen. However, often the reward is unexpected and post reward; the brain must replay the events to find the line of events that led to the reward, thereby strengthening the memory trace.

To know more about the reward pathway in the brain:

“Our memory is not an accurate snapshot of our experiences. We can’t remember everything,” said Daphna Shohamy, senior study author and principal investigator at Columbia’s Mortimer B. Zuckerman Mind Brain Behavior Institute and a professor in the Department of Psychology. “One way the brain solves this problem is by automatically filtering our experiences, preserving memories of important information and allowing the rest fade.”

The effect, however, is not immediate. “The prioritization of rewarding memories requires time for consolidation,” said study co-author Erin Kendall Braun, who conducted this research as part of her doctoral work in the Shohamy lab at the Zuckerman Institute and in psychology at Columbia’s Graduate School of Arts and Sciences. “Our findings suggest that the window of time immediately following the receipt of the reward – as well as a longer overnight window including sleep – work jointly to modulate the sequence of events and shape memory.”

To carry out their study, the researchers asked participants to explore a series of computer-simulated mazes looking for a hidden gold coin, for which they were paid one dollar. The labyrinth was made up of a grid of grey squares, and as participants navigated it, they were shown pictures of everyday objects, such as an umbrella or a mug. The researchers surprised participants with a test of their memory for these objects immediately afterward.

When the memory test was given 24 hours later, participants remembered the objects closest to the reward (the gold coin) but not the others. This suggests the reward had a retroactive effect; a memory for objects that had no particular significance when initially seen was later recalled only because of their proximity to the reward. To the researchers’ surprise, this pattern was not found when they tested memory immediately — the brain needed time to prioritize memory for the events that led to the reward. The test was replicated six times in different variations with a total of 174 participants, with similar results. The image below shows the experimental design to test the retroactive effect of reward on memory.

“The experiment demonstrates that what gets remembered isn’t random and that the brain has mechanisms to preserve memories important for future behavior automatically,” said Shohamy. “For memories to be most useful for future decisions, we need them to be shaped by what matters, and it’s important that this shaping of memory happen before choices are made.” Memory is biased towards activities of high reward.

The previous study published in Neuron showed evidence that humans replay the most rewarding memories to strengthen connection and fix the memory in place when resting. Dr. Charan Ranganathm, senior author and Professor at UC Davis says that “Are you remembering what you really need to know? It could depend on what your brain does while you are at rest."

Despite the findings that provide information onto the memory playback structure, the detailed specifics of how this manifests still eludes the neuroscience community.  The process probably involves dopamine, a chemical known to be essential for signaling rewards, and the hippocampus, the brain region associated with long-term memory. Further research is needed to understand the mechanism by which this occurs. A vital follow-up question would be the effect of adverse events on memory, a study “that would be a lot less fun for the participants,” said Shohamy. But like the current study, “it would help us understand how motivation affects memory and decision making. This understanding would have important implications for education and also for mental health.”

Source: Columbia News, Nature Communications, Medical Express, Neuron

About the Author
  • Aswini Kanneganti is an experienced research scientist from Dallas, Texas. Her interests include neuroscience, medical devices, and neuromodulation.
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