A computational model developed by scientists at the Salk Institute for Biological Studies now suggests that newborn brain cells—generated by the thousands each day—add a time-related code, which is unique to memories formed around the same time.
“By labeling contemporary events as similar, new neurons allow us to recall events from a certain period,” speculates Fred H. Gage, Ph.D., a professor in the Laboratory for Genetics, who led the study published in the Jan. 29, 2009, issue of the journal Neuron. Unlike the kind of time stamp found on digital photographs, however, the neuronal time code only provides relative time.
Ironically, Gage and his team had not set out to explain how the brain stores temporal information. Instead they were interested in why adult brains continually spawn new brain cells in the dentate gyrus, the entryway to the hippocampus. The hippocampus, a small seahorse-shaped area of the brain, distributes memory to appropriate storage sections in the brain after readying the information for efficient recall.
“At least one percent of all cells in the dentate gyrus are immature at any given time,” explains lead author Brad Aimone, a graduate student in the Computational Neuroscience Program at the University of California, San Diego. “Intuitively we feel that those new brain cells have to be good for something, but nobody really knows what it is.”
Each of these newborn neurons undergoes a prolonged maturation process, during which it changes from hyper-excitable to composed and reaches out to mature brain cells that are already well-connected within the established circuitry. Exercise, learning, and environmental enrichment increase proliferation and survival of new neurons, while pathological (chronic) stress and age send their numbers plummeting. Despite an increasing understanding of how new neurons become part of the existing dentate gyrus network, it is still unclear what their exact function is.
Trying to ascertain the newcomers’ job in adult brains, the Salk researchers took every piece of available biological information and fed it into a computer program designed to simulate the neuronal circuits in the dentate gyrus. “Most modelers test a specific hypothesis and build a model around it,” says Aimone. “We tried not to make any big assumptions about the function of new neurons. Instead we asked, ‘What is the biology, and what does the math suggest?’”
It quickly became clear that overly excitable youngsters respond indiscriminately to incoming information. “The circuit in the dentate gyrus is designed to separate incoming memories into distinct events, a process called pattern separation, but immature cells get into the way by blurring the lines,” says Aimone. “And if they keep muddling the picture, there’s almost no point.”
But nothing lasts forever. Even the most highly strung nerve cells that used to get excited by just about anything will eventually quiet down. As they mature into fully functional granule cells, they take their place in the existing circuitry while the next generation of newborn neurons takes their place firing away at new events.
Yet, independent events that had nothing in common but the fact that they occurred around the same time will now be connected forever in our minds—explaining why discussing the movie we saw a couple of months ago might bring back the name of the café we visited afterward but whose name has been eluding us.
“Current thinking holds that when we bring up a certain memory, it passes back to the dentate gyrus, which pulls all related bits of information from their offsite storage,” says Gage. “Our hypothesis suggests that cells that were easily excitable bystanders when the memory was formed are engaged as well, providing a hyperlink between all events that happened during their hyperactive youth.”
The study was funded by the James S. McDonell Foundation, the Kavli Institute for Brain and Mind, the NSF Temporal Dynamics of Learning Center, and the U.S. National Institutes of Health.
Janet Wiles, Ph.D, a professor at the School of Information Technology and Electrical Engineering, University of Brisbane, Australia, also contributed to the study.
The Salk Institute for Biological Studies in La Jolla, California, is an independent nonprofit organization dedicated to fundamental discoveries in the life sciences, the improvement of human health, and the training of future generations of researchers. Jonas Salk, M.D., whose polio vaccine all but eradicated the crippling disease poliomyelitis in 1955, opened the Institute in 1965 with a gift of land from the City of San Diego and the financial support of the March of Dimes.
Gina Kirchweger | Newswise Science News
Cryo-electron microscopy achieves unprecedented resolution using new computational methods
24.03.2017 | DOE/Lawrence Berkeley National Laboratory
How cheetahs stay fit and healthy
24.03.2017 | Forschungsverbund Berlin e.V.
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
24.03.2017 | Materials Sciences
24.03.2017 | Physics and Astronomy
24.03.2017 | Physics and Astronomy