Not
sure what we can do with this yet but it seems we are getting a far clearer
understanding about what is happening during the biological process of learning. The logic of the process is also been
developed.
What
I would like to see is a clear understanding of time frames for various processes
to firm up.
This
is a fine snapshot of our present understanding.
Competition Between Brain Cells Spurs Memory Circuit Development
Released: 6/20/2011 12:00 PM EDT
Newswise — ANN ARBOR, Mich. — Scientists at the University of Michigan
Health System have for the first time demonstrated how memory circuits in the
brain refine themselves in a living organism through two distinct types of
competition between cells.
Their results, published today in Neuron, mark a step forward in
the search for the causes of neurological disorders associated with abnormal
brain circuits, such as Alzheimer’s disease, autism and schizophrenia.
“Much of our understanding of the brain’s wiring has come from studying
our sensory and motor systems, but far less is understood about the mechanisms
that organize neural circuits involved in higher brain functions, like learning
and memory,” says senior author Hisashi Umemori, M.D., Ph.D., assistant
research professor at U-M’s Molecular and Behavioral Neuroscience Institute and
assistant professor of biological chemistry at the U-M Medical School.
Brain cells grow and extend along pathways to link different parts of
the brain, Umemori explains. As the brain develops, these connections fine-tune
themselves and become more efficient. Problems with this refinement process may
be responsible for some neurological disorders.
“We wanted to know how brain circuits become more efficient during the
brain’s development,” Umemori adds. “Does the brain choose to keep good
connections and get rid of bad ones and, if so, how?”
To examine how neural activity organizes memory circuits, researchers
used mice that had been genetically modified so that neurons of interest
purposefully could be switched off.
The scientists focused on an important connection between the
hippocampus, which is crucial for learning and memory, and the cerebral cortex,
which is key for perception and awareness. They deactivated about 40 percent of
the neurons in the connection and, over a matter of days, watched as the brain
eliminated the inactive neural connections and kept only the active ones. A subsequent
part of the experiment showed that if all the neurons were deactivated, their
connections were not eliminated.
“This tells us that the brain has a way of telling among a group of
neurons which connections are better than others,” Umemori says. “The neurons
are in competition with each other. So when they’re all equally bad, none can
be eliminated.”
The researchers also looked at a part of the hippocampus called the
dentate gyrus, which is only one of two areas of the brain that continues to
generate new neurons throughout life. Here they found a second distinct type of
competition: newborn cells were competing with mature cells, rather competition
occurring between mature cells.
When scientists blocked the dentate gyrus’ ability to make new cells, the
elimination stopped and the brain kept the existing cells even if they were
deactivated.
“The better the brain is at eliminating bad connections to keep the
circuitry at its most efficient, the more efficient learning and memory will be
as well,” Umemori explains.
He adds, “The better we understand how these mechanisms work,
the better we’ll be able to understand what’s happening when they aren’t
working.”
Additional Authors: Masahiro Yasuda, Ph.D.; Erin M. Johnson-Venkatesh,
Ph.D.; Helen Zhang, M.S.; Jack M. Parent, M.D.; Michael A. Sutton, Ph.D.; all
of U-M
Funding: U-M Center for Organogenesis, Ester A. & Joseph
Klingenstein Fund, the Edward Mallinckrodt Jr. Foundation, the March of Dimes
Foundation, the Whitehall
Citation: “Multiple Forms of Activity-Dependent Competition Refine
Hippocampal Circuits In Vivo,” Neuron, June 22, 2011
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