ScienceDaily (Dec. 16, 2009) — The conversations neurons have as they form and recall memories have been decoded by Medical College of Georgia scientists.
The breakthrough in recognizing in real time the formation and recollection of a memory opens the door to objective, thorough memory studies and eventually better therapies, said Dr. Joe Tsien, neuroscientist and co-director of MCG's Brain & Behavior Discovery Institute. He is corresponding author on the study published Dec. 16 in PLoS ONE.
Artist's rendering of neurons. (Credit: iStockphoto)
"It's a beginning, a first glimpse of a memory," Dr. Tsien said. "For the first time it gives us the ability to look at the brain dynamic and tell what kind of memory is formed, what are the components of the memory and how the memory is retrieved at the network level." The finding could help pinpoint at what stage memory formation is flawed and whether drugs are improving it.
For their studies, MCG scientists combined new technology and computational methods with century-old Pavlovian conditioning.
In the memory center of the brain, they used 128 electrodes capable of monitoring a handful of neurons each to simultaneously record the conversations of 200 to 300 neurons as mice learned to associate a certain tone with a mild foot shock 20 seconds later.
A computational algorithm translated the neuronal chatter into a discernable and dynamic activity pattern that provided scientists a trace or picture of what the memory looked like as it was formed and recalled.
"By listening to the neuronal activity we were able to decipher the real-time dynamic pattern and the meaning of those conversations so this is really satisfying," said Dr. Tsien, the Georgia Research Alliance Eminent Scholar in Cognitive and Systems Neurobiology.
The trace changed slightly each time it was recalled -- likely as the mood or situation of the rodent changed -- but still remained recognizable as a specific memory.
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Journal Reference:
Guifen Chen, L. Phillip Wang, Joe Z. Tsien*
Brain and Behavior Discovery Institute and Department of Neurology, School of Medicine, Medical College of Georgia, Augusta, Georgia, United States of America
PLoS ONE, 2009; DOI: 10.1371/journal.pone.0008256
Abstract
One of the fundamental goals in neurosciences is to elucidate the formation and retrieval of brain's associative memory traces in real-time. Here, we describe real-time neural ensemble transient dynamics in the mouse hippocampal CA1 region and demonstrate their relationships with behavioral performances during both learning and recall. We employed the classic trace fear conditioning paradigm involving a neutral tone followed by a mild foot-shock 20 seconds later. Our large-scale recording and decoding methods revealed that conditioned tone responses and tone-shock association patterns were not present in CA1 during the first pairing, but emerged quickly after multiple pairings. These encoding patterns showed increased immediate-replay, correlating tightly with increased immediate-freezing during learning. Moreover, during contextual recall, these patterns reappeared in tandem six-to-fourteen times per minute, again correlating tightly with behavioral recall. Upon traced tone recall, while various fear memories were retrieved, the shock traces exhibited a unique recall-peak around the 20-second trace interval, further signifying the memory of time for the expected shock. Therefore, our study has revealed various real-time associative memory traces during learning and recall in CA1, and demonstrates that real-time memory traces can be decoded on a moment-to-moment basis over any single trial.
Citation: Chen G, Wang LP, Tsien JZ (2009) Neural Population-Level Memory Traces in the Mouse Hippocampus. PLoS ONE 4(12): e8256. doi:10.1371/journal.pone.0008256
Editor: Ehsan Arabzadeh, University of New South Wales, Australia
Received: October 7, 2009; Accepted: November 19, 2009; Published: December 16, 2009
Copyright: © 2009 Chen et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This research was supported by funds from National Institute of Mental Health (NIMH), National Institute of Aging (NIA), MCG fund, and Georgia Research Alliance (All to JZT). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
* E-mail: jtsien@mcg.edu
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