Brain May Grow
New Cells Daily

"Brain
May Grow New Cells Daily," by Nicholas Wade,
A new challenge to the longstanding belief that adults never generate new
brain cells, biologists at Princeton University have found that thousands
of freshly born neurons arrive each day in the cerebral cortex, the outer
rind of the brain where higher intellectual functions and personality are
centered.
Though based on research in monkeys, the finding is likely to prove true of
people, too.
If so, several experts said, it may overturn ideas about
how the human brain works and open new possibilities for treating
degenerative brain diseases.
MORE GRAY MATTER
Researchers have found that the brains of macaque monkeys
produce new brain cells that migrate to the cerbral cortex,
where higher functioning is centered.
Frontal view of brain
1. Neural stem cells, neurons in their early stage of
development, are produced in the central area of the brain.
2. The neurons develop as they migrate.
3. The mature neurons reach the outer cortex, the location
of advanced functions in the brain.
Source: Science |
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If the new brain cells, or neurons, are involved in memory and learning --
perhaps with each day's batch of new cells recording that day's experiences
-- scientists will have to make major revisions in the longtime view that the
adult brain's neurons are static in number and that memory is stored only in
the way they interconnect.
In addition, if the brain's cells are in constant turnover,
as the new finding suggests, physicians may discover ways to
use the brain's natural regeneration system for replacing cells
that are lost in diseases of aging.
The discovery, by Elizabeth Gould and Charles G. Gross, is reported
in Friday's issue of the journal Science.
The belief that the adult brain does not make new cells rested
on careful, well-known studies by Pasko Rakic of Yale University,
who looked for the formation of new neurons in the monkey brain
and found none.
But the Princeton work is likely to be convincing, because it
builds on previous reports of brain cell turnover, notably by
Fernando Nottebohm of Rockefeller University, who showed that
canaries grow new neurons to learn new songs, and recent studies
showing that new cells are formed in the hippocampus, a brain
region where initial memories of faces and places are formed.
"The scientific community can easily believe something
it is 50 percent ready to absorb, but not something that comes
out of left field," said Eric R. Kandel, a leading neuroscientist
at Columbia University. "But here, we are prepared for it."
Kandel compared the likely change in view to the paradigm shifts
described by the historian of science Thomas Kuhn as occurring
when one major scientific theory is replaced by another.
Although the new study was done in macaque monkeys and has yet
to be confirmed in humans, as fellow primates monkeys are usually
quite predictive of what occurs in people.
Gould, who has studied new cell formation in the hippocampus,
and Gross, an expert on the cerebral cortex, injected macaques
with a chemical that is incorporated in the new DNA formed when
a cell divides.
They found that a stream of new neurons were generated in the
monkeys' brains in a zone just above the brain's fluid-filled
central chambers. This zone was recently identified by other
scientists as the home of the brain's stem cells, the source
cells from which an organ is replenished.
The new neurons migrated toward the cortex, matured and sent
out axons to make connections with other brain cells, the Princeton
biologists found.
The researchers looked for new neurons in four areas of the
cortex, and found them in three areas where memories are known
to be stored: the frontal cortex, used for decision-making, and
two areas on the side of the brain used for visual recognition.
No new neurons were detected in the fourth area, the striate
cortex, a region at the back of the head that simply processes
visual information from the eyes and passes it on to other parts
of the cortex.
Whatever the new cells are doing in the cortex, they
affect regions of the brain that are central to human thought
and identity.
The Princeton work, said Ronald D. G. McKay, an expert on brain
stem cells at the National Institutes of Health, "places
new neurons in the region of the brain involved in the highest
level of personality: it's the frontal cortex that is important
in determining who you are in a very human way."
Gould said it was possible that the new neurons arriving in
the cortex would be particularly sensitive to recording information
for a certain period while they matured.
"They would become integrated in the circuitry and represent
the information being learned at that particular time," she
said, after which they would not record anything more.
In other words, the conveyor belt of new neurons might record
successive days' experiences almost like a moving tape.
"We know the characteristic of memory is that events are
tagged with times," Gross said. "We have no idea how
that is done. But since we have now shown there are new cells
added every day, which cover a spectrum of ages, these cells
could possibly provide the substrate for the temporal dimension
of memory."
Kandel, of Columbia University, said the idea was perfectly
possible, given how little was now known about the brain's system
for ultimate long-term memory storage.
"How do you distinguish the memory of 20 years ago from
the memory of 30 years ago? You would have to mark the birthday
of the cell in some way," Kandel said, suggesting that the
train of new neurons offered a plausible mechanism whereby the
brain might somehow do this.
The notion that new memories are stored in a train of new nerve
cells was advocated in the 1960's by Joseph Altman, then of the
Massachusetts Institute of Technology. But his proposal was not
widely accepted. And when Rakic, an authority on neuron formation
in the embryonic monkey brain, reported in 1985 that no new neurons
were formed in the adult monkey's brain, this became the accepted
view.
Even when Gould and others showed recently that new cells were
formed in the hippocampus, Rakic argued that this was a primitive
area of the brain -- even reptiles have a hippocampus -- and
that brain organs acquired more recently in evolution, like the
primates' cerebral cortex, would not be expected to behave the
same way.
Gould said it was this argument that had made her determined
to look for new cells being formed in the cerebral cortex, despite
the expense of doing work on monkeys and the risk in "redoing
an experiment that a very well respected person," Rakic,
had already performed.
Rakic's office said he was traveling yesterday and unavailable
for comment.
If indeed the brain is constantly renewing the cells in its
cortex, hippocampus and maybe other areas, the prospects for
learning how to repair the aged or damaged brain begin to look
much more hopeful.
"Degenerative diseases of the brain are really defined
by loss of nerve cells," Kandel said. Though diseases like
Parkinson's affect specific areas of the brain, it might become
possible to channel young new neurons into the areas of disease. "This
is pie in the sky," he said, "but at least there is
now the possibility of thinking about it."
William T. Greenough, a neuroscientist at the University
of Illinois, said the Princeton work created a "whole new ball
game" for addressing brain diseases, by harnessing the brain's
own restorative potential.
The Princeton biologists plan to follow up their discovery by
blocking the formation of new neurons in monkeys' brains and
seeing what happens. If the new neurons are essential for memory
and learning, then serious deficits should appear in the monkeys'
performance.
The researchers as yet have no idea whether the loss of brain
cells and the generation of new ones are separate events or part
of the same cycle.
"Our discovery," Gross said, "suggests
more questions than answers."
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Salk Institute Study Finds Brains
Can Grow New Cells
Brain nutrient can help maximize memory.
by Ronald M. Lawrence, M.D., Ph.D.
According to a recently completed animal study conducted by the Salk Institute,
it turns out that regular exercise helps an "old brain" build new
brain cells (Van Praag 2002). Just as importantly, researchers have found that
the daily use of powerful brain nutrients can support the brain by boosting
membrane function (Kidd 1998). It's all good news for aging brains.
The Salk Institute study, published in the science journal Nature, found that
in mice, new brain cells were generated in the hippocampus, the area of the
brain responsible for learning and memory. After only four months, these new
brain cells were found to mature into functional neurons (Van Praag 2002).
The researchers don't know what these new brain cells actually do, but they
hope to someday replicate the effects in other areas of the brain. Imagine
the implications for neurodegenerative diseases like Alzheimer's or for diseases
such as stroke that destroy brain cells (Newswise 2002).
Nutrient to Assist Thinking and Memory
For the present, there is encouraging news about maintaining brain health,
especially through the use of the naturally occurring compound phosphatidylserine
(PS). PS is a key building block for brain cells. Specifically, it helps maintain
the integrity and the fluidity of brain cell membranes, which are a kind of
sheath that has many functions. Cell membranes protect the cells while simultaneously
letting nutrients in and waste products out, and their flexibility is crucial
for enhancing swift communication between neurons (Kidd 1998).

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