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Developmental biology - Memory

Past Memories Help Us Juggle Information

Our brain has limited storage space, only keeping representations of events for milliseconds...


Everyday tasks require people to combine information from multiple sources. For example, when driving.

All information is stored in working memory, a limited-capacity system allowing humans to 'represent' information for short intervals - milliseconds. Working memory assigns information different levels of importance. In heavy traffic you must maintain accurate 'representations' of how far you are from other cars. As the relative importance of information changes at a moment's notice, like when a car suddenly cuts you off, you immediately recalculate distance based on the last cue stored in your working memory.

Re-prioritizing 'representations' is critical for many simple tasks, yet little is known about how our brain re-prioritizes information change, if at all.

In a study published in The Journal of Neuroscience, scientists from Florida Atlantic University (FAU) examined how brains store 'representations'. Using electroencephalography (EEG), they tracked brain activity while participants were asked to hold a set of cues in working memory. Some participants were shown a cue that predicted which location they would be asked to report at the end of the trial - giving them strong incentive to prioritize that location over a non-cued location.

Results from the study show that cues can influence the neural representation of cued and non-cued locations, but the effect of the cue depends on when it appears. When no cue was given, neural 'representation' of each location gradually decayed with time. When the cue appeared immediately after a memory display, neural 'representation' of the cue location remained strong and constant throughout the remaining storage interval, and the 'representation' of the non-cued location was quickly washed away.
By using EEG to track neural 'representations' of each location, researchers could see how those 'representations' are influenced by cues. They demonstrated that cues have different effects on neural 'representations' depending on when they appear. This suggests the brain has several mechanisms it uses to boost memory performance following sudden changes in priority or relevance.

"It's been difficult to pinpoint exactly how the brain re-prioritizes information following changes in the environment, in part because earlier studies have relied on relatively slow measures of brain activity. The benefit of EEG is that we can track changes in brain activity on a scale of a few to tens of milliseconds - about an order of magnitude faster than other methods such as functional MRI," said Edward Ester PhD, assistant professor, Department of Psychology, FAU's Charles E. Schmidt College of Science, and a member of the FAU Brain Institute. "Our findings suggest the brain can use several different methods to re-prioritize mental 'representations' depending on how long they are stored."

A key insight from the study came from the pattern observed when a cue is presented mid-way through a storage interval. In the first half of the storage interval, the neural representation of each location decayed with time. However, decay was partly reversed for that same location when the cue was presented, suggesting the brain is able to "boost" representation of a now-relevant location which facilitates memory.
"Working memory capacity is strongly correlated with a person's intelligence. Given that dysfunction in working memory is a major symptom in common psychiatric disorders such as schizophrenia and autism, it's important that neuroscientists gain a true understanding of how it works."

Asal Nouri, doctoral student, Department of Psychology, Center for Complex Systems and Brain Sciences, FAU Brain Institute, Florida Atlantic University, co-author of the paper with Laura Rodriguez.

Abstract
Working memory (WM) enables the flexible representation of information over short intervals. It is well-established that WM performance can be enhanced by a retrospective cue presented during storage, yet the neural mechanisms responsible for this benefit are unclear. Here, we tested several explanations for retro-cue benefits by quantifying changes in spatial WM representations reconstructed from alpha-band (8-12 Hz) EEG activity recorded from human participants (both sexes) before and after presentation of a retrospective cue. This allowed us to track cue-related changes in WM representations with high temporal resolution (tens of milliseconds). Participants encoded the locations of two colored discs for subsequent report. During neutral trials an uninformative cue instructed participants to remember the locations of both discs across a blank delay, and we observed a monotonic decrease in the fidelity of reconstructed spatial WM representations with time. During valid trials a 100% reliable cue indicated the color of the disc participants would be probed to report. Critically, valid cues were presented immediately after termination of the encoding display (“valid early”, or VE trials) or midway through the delay period (“valid late” or VL trials). During VE trials the gradual loss of location-specific information observed during neutral trials was eliminated, while during VL trials it was partially reversed. Our findings suggest that retro-cues engage several different mechanisms that together serve to mitigate information loss during WM storage.

Significance Statement
Working memory (WM) performance can be improved by a cue presented during storage. This effect, termed a retrospective cue benefit, has been used to explore the limitations of attentional prioritization in WM. However, the mechanisms responsible for retrospective cue benefits are unclear. Here we tested several explanations for retrospective cue benefits by examining how they influence WM representations reconstructed from human EEG activity. This approach allowed us to visualize, quantify, and track the effects of retrospective cues with high temporal resolution (on the order of tens of milliseconds). We show that under different circumstances retrospective cues can both eliminate and even partially reverse information loss during WM storage, suggesting that retrospective cue benefits have manifold origins.

Authors
Edward F. Ester, Asal Nouri and Laura Rodriguez


About the FAU Brain Institute:
Inaugurated in 2016 on the John D. MacArthur Campus in Jupiter, Fla., the FAU Brain Institute supports research, education and community outreach among more than 100 faculty level researchers at FAU and its affiliate research centers. One of FAU's four pillars that guide the University's goals and strategic actions, the Institute seeks to unlock the secrets of brain development, function and plasticity and how the mechanisms uncovered can be compromised to drive devastating brain disorders. From the study of neuronal development and signaling to investigations of brain diseases including addiction, autism, Parkinson's and Alzheimer's disease, researchers from FAU's Brain Institute seek to generate knowledge that benefits society. For more information about the Institute and its members, visit http://www.ibrain.fau.edu.

About Florida Atlantic University:
Florida Atlantic University, established in 1961, officially opened its doors in 1964 as the fifth public university in Florida. Today, the University, with an annual economic impact of $6.3 billion, serves more than 30,000 undergraduate and graduate students at sites throughout its six-county service region in southeast Florida. FAU's world-class teaching and research faculty serves students through 10 colleges: the Dorothy F. Schmidt College of Arts and Letters, the College of Business, the College for Design and Social Inquiry, the College of Education, the College of Engineering and Computer Science, the Graduate College, the Harriet L. Wilkes Honors College, the Charles E. Schmidt College of Medicine, the Christine E. Lynn College of Nursing and the Charles E. Schmidt College of Science. FAU is ranked as a High Research Activity institution by the Carnegie Foundation for the Advancement of Teaching. The University is placing special focus on the rapid development of critical areas that form the basis of its strategic plan: Healthy aging, biotech, coastal and marine issues, neuroscience, regenerative medicine, informatics, lifespan and the environment. These areas provide opportunities for faculty and students to build upon FAU's existing strengths in research and scholarship. For more information, visit http://www.fau.edu.


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Sep 20, 2018   Fetal Timeline   Maternal Timeline   News   News Archive




The brain uses different methods to store and keep order in its limited space. Cues for representations of events are only stored for milliseconds in the brain. Each cue triggering another related cue,
until all are retreived as a complete memory. Illustration in the public domain.


Phospholid by Wikipedia