Old and stooped in nostalgia? Researchers explain that this phenomenon, with the help of a computer model, can be connected to a study of the newborn brain cells add a time-related code.
However, the model developed by scientists at the Salk Institute for Biological Studies showed that, unlike the kind of time stamp found on digital photographs, neuronal time code only provides relative time.
"By labelling 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.
The researchers, instead of finding out how the brain stores temporal information, set out to know why adult brains continually spawn new brain cells in the dentate gyrus, the entryway to the hippocampus.
The hippocampus, 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. Intuitively we feel that those new brain cells have to be good for something, but nobody really knows what it is," explained lead author Brad Aimone, a graduate student in the Computational Neuroscience Program at the University of California, San Diego.
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.
In order to find out the newcomers' job in adult brains, the 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. 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?'" said Aimone.
And it was found 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. And if they keep muddling the picture, there's almost no point," said Aimone.
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.
Still, 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 caf? we visited afterward but whose name has been eluding us.
The study is published in the latest issue of the journal Neuron.