To keep, or not to keep ‒ that is the question.

(Cohen 2016)

Memory is very a interesting yet highly complex process and therefore mostly still a mystery. However, much work is currently being done to help us understand the mechanism by which we encode, store and retrieve memories.

The article titled “Memory replay prioritizes high-reward memories,” recently published by ScienceDaily, discusses a study that looked at how high-rewards can affect our memory. Professor Charan Ranganath, a neuroscientist at UC Davis, and his postdoctoral fellow, Matthias Gruber conducted the study using fMRI scanning to view brain activity during reward-motivated learning as well as at rest both before and after learning. During the test, participants were asked questions like, “Do these objects weigh more than a basketball?” and were told that they would receive either a large or small monetary reward for providing a correct answer. The objects on a background image for context were presented and at the end of a series, the participants were told how much money they had accumulated. After a resting period, they were given a surprise memory test for objects that were shown. Data collected showed that for objects that had been associated with a high value reward, participants were able to remember both the objects and their backgrounds. Researchers also found that the pattern of activity that had been observed while participants performed the task was also seen during the period of rest that followed it. They concluded that during this period they were strengthening connections and fixing memories in place by replaying the rewarding memories. In essence, the study shows that our brain prioritizes memories that are deemed to be more valuable by replaying them while we are at rest.

A very similar study performed by Michael Cohen, a postdoctoral researcher at Northwestern University looked the neural mechanisms by which the brain does the prioritizing observed in the previous study. In his paper, titled,  Effects of aging on value-directed modulation of semantic network activity during verbal learning, Dr. Cohen discusses a study done in which he looked at whether the temporal and spatial patterns of brain activation differed in older adults when compared to younger adults during encoding of high and low value words. In the study, participants were given a cue indicating how many points they would receive if they remembered the word they were about to see in a future memory recall test. Using fMRI scanning, researchers analyzed the brain activity that occurred and found that individuals regulated activity depending on whether the word had a high value or a low one across the left-lateralized brain regions that are involved in semantic processing. In particular, young adults showed increased activity in those areas when the word was associated with a high value while older adults refrained from using those areas when words associated with low values were presented.

By using a similar reward-based paradigm, both studies offer interesting insights into the process by which the brain decides to keep what it does. In Dr. Cohen’s study we see that both younger and older adults use left lateralized brain regions to encode information they deem valuable although through different mechanisms. Dr. Gruber’s study explains what happens after we have decided that information should be kept. His study suggests we replay memories that are rewarding in order to fix them in place. Therefore the answer to question, to keep or not to keep, depends on whether the information is of high value.

References

• Cohen, M. S., Rissman, J., Suthana, N. A., Castel, A. D., & Knowlton, B. J. (2016). Effects of aging on value-directed modulation of semantic network activity during verbal learning. NeuroImage, 125, 1046-1062.

• University of California - Davis. (2016, February 12). Memory replay prioritizes high-reward memories. ScienceDaily. www.sciencedaily.com/releases/2016/02/160212130132.htm