Sara S
02-12-2010, 08:33 AM
from delancyplace.com:
In today's encore excerpt - the brain can grow
new neurons, but these disappear unless cognitively
challenged:
"Fresh neurons arise in the brain every day. ... Recent
work, albeit mostly in rats, indicates that learning
enhances the survival of new neurons in the adult
brain, and the more engaging and challenging the
problem, the greater the number of neurons that stick
around. These neurons are then presumably
available to aid in situations that tax the mind. It
seems, then, that a mental workout can buff up the
brain, much as physical exercise builds up the
body. ...
"In the 1990s scientists rocked the field of
neurobiology with the startling news that the mature
mammalian brain is capable of sprouting new
neurons. Biologists had long believed that this talent
for neurogenesis was reserved for young, developing
minds and was lost with age. But in the early part of
the decade Elizabeth Gould, then at the Rockefeller
University, demonstrated that new cells arise in the
adult brain - particularly in a region called the
hippocampus, which is involved in learning and
memory. ...
"Studies indicate that in rats, between 5,000 and
10,000 new neurons arise in the hippocampus every
day. (Although the human hippocampus also
welcomes new neurons, we do not know how many.)
The cells are not generated like clockwork, however.
Instead their production can be influenced by a
number of different environmental factors. For
example, alcohol consumption has been shown to
retard the generation of new brain cells. And their birth
rate can be enhanced by exercise. Rats and mice that
log time on a running wheel can kick out twice as
many new cells as mice that lead a more sedentary
life. ...
"Exercise and other actions may help produce extra
brain cells. But those new recruits do not necessarily
stick around. Many if not most of them disappear
within just a few weeks of arising. Of course, most
cells in the body do not survive indefinitely. So the fact
that these cells die is, in itself, not shocking. But their
quick demise is a bit of a puzzler. Why would the brain
go through the trouble of producing new cells only to
have them disappear rapidly?
"From our work in rats, the answer seems to be: they
are made 'just in case.' If the animals are cognitively
challenged, the cells will linger. If not, they will fade
away."
Tracey J. Shors, "Saving New Brain Cells,"
Scientific American, March 2009, pp. 47-48.
And, further:
In today's excerpt - human brains have almost
all of their 100 billion neurons in place at
birth, with some 250,000 being born every
minute during gestation, and these brains are
almost identical to all other human brains,
since even a slight variation can be lethal:
The trajectory by which a fusion of human
sperm and
ovum results, over nine months gestation, in
some 3-4 kilos of baby,
fully equipped with internal organs, limbs,
and a brain with most of its
100 billion neurons in place, is relatively
easy to describe, even
when it is hard to explain.
All humans are alike in very
many respects, all are different in some. (No
two individuals, not even
monozygotic twins, are entirely identical,
even at birth.) Yet chemically,
anatomically and physiologically there is
astonishingly little obvious variation to be
found between brains, even from people from
widely different
populations. Barring gross developmental
damage, the same structures
and substances repeat in every human brain,
from the chemistry of their
neurotransmitters to the wrinkles on the
surface of the cerebral cortex.
Humans differ substantially in size and
shape, and so do our brains, but
when a correction is made for body size, then
our brains are closely
matched in mass and structure, though men's
brains are slightly heavier
on average than are women's. So similar are
they though, that imagers
using PET (positron emission tomography) and
MRI (magnetic resonance imaging) have been
able to develop algorithms by which they can
transform and project the image derived from
any individual into a 'standard' brain.
Brains are so finely tuned to function, so
limited by
constraints, that anything more than
relatively minor variation is simply
lethal.
Of no body organ is the developmental
sequence more simultaneously dramatic and
enigmatic than the brain. How to explain the
complexity and apparent precision with which
individual neurons are
born, migrate to their appropriate final
sites, and make the connections
which ensure that the newborn on its arrival
into the outside world has
a nervous system so fully organized that the
baby can already see, hear,
feel, voice her needs, and move her limbs?
The fact that this is possible
implies that the baby at birth must have most
of her complement of
neurons already in place - if not the entire
100 billion, then getting on
for that number. If we assume a steady birth
of cells over the whole
nine months - although of course in reality
growth is much more
uneven, with periodic growth spurts and lags
- it would mean some
250,000 nerve cells being born every minute
of every day over the period.
As if this figure is not extraordinary
enough, such is the density of
connections between these neurons that we
must imagine up to 30,000
synapses a second being made over the period
for every square
centimeter of newborn cortical surface. And
to this rapid rate of production must be
added that of the glia, packing the white
matter below the
cortex and surrounding the neurons within it
- though admittedly they
do not reach their full complement by birth
but continue to be generated throughout
life.
Steven Rose, The Future of the Brain, Oxford,
Copyright 2005 by Steven Rose, pp. 57-63.
----------------------------------------
In today's encore excerpt - the brain can grow
new neurons, but these disappear unless cognitively
challenged:
"Fresh neurons arise in the brain every day. ... Recent
work, albeit mostly in rats, indicates that learning
enhances the survival of new neurons in the adult
brain, and the more engaging and challenging the
problem, the greater the number of neurons that stick
around. These neurons are then presumably
available to aid in situations that tax the mind. It
seems, then, that a mental workout can buff up the
brain, much as physical exercise builds up the
body. ...
"In the 1990s scientists rocked the field of
neurobiology with the startling news that the mature
mammalian brain is capable of sprouting new
neurons. Biologists had long believed that this talent
for neurogenesis was reserved for young, developing
minds and was lost with age. But in the early part of
the decade Elizabeth Gould, then at the Rockefeller
University, demonstrated that new cells arise in the
adult brain - particularly in a region called the
hippocampus, which is involved in learning and
memory. ...
"Studies indicate that in rats, between 5,000 and
10,000 new neurons arise in the hippocampus every
day. (Although the human hippocampus also
welcomes new neurons, we do not know how many.)
The cells are not generated like clockwork, however.
Instead their production can be influenced by a
number of different environmental factors. For
example, alcohol consumption has been shown to
retard the generation of new brain cells. And their birth
rate can be enhanced by exercise. Rats and mice that
log time on a running wheel can kick out twice as
many new cells as mice that lead a more sedentary
life. ...
"Exercise and other actions may help produce extra
brain cells. But those new recruits do not necessarily
stick around. Many if not most of them disappear
within just a few weeks of arising. Of course, most
cells in the body do not survive indefinitely. So the fact
that these cells die is, in itself, not shocking. But their
quick demise is a bit of a puzzler. Why would the brain
go through the trouble of producing new cells only to
have them disappear rapidly?
"From our work in rats, the answer seems to be: they
are made 'just in case.' If the animals are cognitively
challenged, the cells will linger. If not, they will fade
away."
Tracey J. Shors, "Saving New Brain Cells,"
Scientific American, March 2009, pp. 47-48.
And, further:
In today's excerpt - human brains have almost
all of their 100 billion neurons in place at
birth, with some 250,000 being born every
minute during gestation, and these brains are
almost identical to all other human brains,
since even a slight variation can be lethal:
The trajectory by which a fusion of human
sperm and
ovum results, over nine months gestation, in
some 3-4 kilos of baby,
fully equipped with internal organs, limbs,
and a brain with most of its
100 billion neurons in place, is relatively
easy to describe, even
when it is hard to explain.
All humans are alike in very
many respects, all are different in some. (No
two individuals, not even
monozygotic twins, are entirely identical,
even at birth.) Yet chemically,
anatomically and physiologically there is
astonishingly little obvious variation to be
found between brains, even from people from
widely different
populations. Barring gross developmental
damage, the same structures
and substances repeat in every human brain,
from the chemistry of their
neurotransmitters to the wrinkles on the
surface of the cerebral cortex.
Humans differ substantially in size and
shape, and so do our brains, but
when a correction is made for body size, then
our brains are closely
matched in mass and structure, though men's
brains are slightly heavier
on average than are women's. So similar are
they though, that imagers
using PET (positron emission tomography) and
MRI (magnetic resonance imaging) have been
able to develop algorithms by which they can
transform and project the image derived from
any individual into a 'standard' brain.
Brains are so finely tuned to function, so
limited by
constraints, that anything more than
relatively minor variation is simply
lethal.
Of no body organ is the developmental
sequence more simultaneously dramatic and
enigmatic than the brain. How to explain the
complexity and apparent precision with which
individual neurons are
born, migrate to their appropriate final
sites, and make the connections
which ensure that the newborn on its arrival
into the outside world has
a nervous system so fully organized that the
baby can already see, hear,
feel, voice her needs, and move her limbs?
The fact that this is possible
implies that the baby at birth must have most
of her complement of
neurons already in place - if not the entire
100 billion, then getting on
for that number. If we assume a steady birth
of cells over the whole
nine months - although of course in reality
growth is much more
uneven, with periodic growth spurts and lags
- it would mean some
250,000 nerve cells being born every minute
of every day over the period.
As if this figure is not extraordinary
enough, such is the density of
connections between these neurons that we
must imagine up to 30,000
synapses a second being made over the period
for every square
centimeter of newborn cortical surface. And
to this rapid rate of production must be
added that of the glia, packing the white
matter below the
cortex and surrounding the neurons within it
- though admittedly they
do not reach their full complement by birth
but continue to be generated throughout
life.
Steven Rose, The Future of the Brain, Oxford,
Copyright 2005 by Steven Rose, pp. 57-63.
----------------------------------------