Hi brunews:
Thank you for the fascinating question- it certainly stretched my
brain and rearranged a few of my connections! ;-)
Connections between neurons are more commonly referred to as
"synapses".
After quite a bit of searching, I found a matching graph on page 8 of
a 44 page presentation - "Implementing California's Children's
Environmental Health Protection Act" - by Dr. Melanie Marty of the
California Environmental Protection Agency.
The presentation can be viewed in PDF format at:
Minnesota Department of Health
http://www.health.state.mn.us/divs/eh/children/seminars/martypp.pdf
Scroll down to page 8 and have a look at the figure labeled "The
Brain: Synaptic Pruning".
This shows (as did my other research) that the number of synapses
increases rapidly from birth until age 2 - 3, decreases rapidly from
synaptic pruning during the next 12 - 13 years (the most rapidly
during the ages 10 -15), and decreases more gradually during adult
life.
For a textual overview of Dr. Marty's entire presentation, go to:
http://www.health.state.mn.us/divs/eh/children/seminars/marty.html
For a very compact description of synapse growth and synaptic pruning,
please read:
Brain Plasticity: What Is It?
http://faculty.washington.edu/chudler/plast.html
where it is written:
"Over the first few years of life, the brain grows rapidly. As each
neuron matures, it sends out multiple branches (axons, which send
information out, and dendrites, which take in information), increasing
the number of synaptic contacts and laying the specific connections
from house to house, or in the case of the brain, from neuron to
neuron. At birth, each neuron in the cerebral cortex has approximately
2,500 synapses. By the time an infant is two or three years old, the
number of synapses is approximately 15,000 synapses per neuron
(Gopnick, et al., 1999). This amount is about twice that of the
average adult brain. As we age, old connections are deleted through a
process called synaptic pruning."
While I realize that the above graph does not include the "fetal time"
(as you put it from minus nine months), the following information will
help you extrapolate:
It is known that synaptic development in the fetus starts around the
three month, or thirteen week, timeframe. Before that, the neurons are
too busy shifting around to their correct positions.
"By the age of three months gestation, the brain of the fetus already
has considerable complexity (Kotulak, 1996). The brain stem is formed
and functioning. The cerebrum is forming and has begun to function.
Most brain cells are formed by the first three months and are moving
into place. Once migrated, brain cells develop many dendrites
(branches of "antennae") that receive messages from other brain cells.
They also develop axons (a long "leg" with a "foot" of little
branches) which transmit a message to another cell in the form of an
electrical impulse. A brain cell’s axon transmits it’s message to
another cell’s dendrite by releasing a chemical or neurotransmitter.
The neurotransmitter is actually released into a space between the
axon and dendrite, called a synapse. In this way, the brain cells
"talk" to each other and process their "conversation." Cells that have
migrated to the auditory and memory sites of the cerebrum are
beginning to function and interact."
From: http://www.kidfaith.org/Articles.htm
The synapses continue growing rapidly over the next six month of
pregnancy until they reach the figure shown at age 0 (NB) on the
graph.
I hope that this answer is sufficient for your needs. From the other
questions I've see you asking, you must be putting something pretty
interesting together. :-)
If you need any clarifications of what I've presented, please ask me
using the Clarification process - before you rate this answer.
Thanks!
websearcher-ga
Search Strategies on Google:
graph number synapses age
://www.google.com/search?q=graph+number+synapses+age&hl=en&lr=&ie=UTF-8&start=10&sa=N
"The Brain: Synaptic Pruning"
://www.google.com/search?hl=en&lr=&ie=ISO-8859-1&q=%22The+Brain%3A+Synaptic+Pruning%22
"Synaptic Pruning"
://www.google.com/search?hl=en&lr=&ie=ISO-8859-1&q=%22Synaptic+Pruning%22+
synapses growth fetus
://www.google.com/search?hl=en&lr=&ie=ISO-8859-1&q=synapses+growth+fetus
synapses growth begins fetus
://www.google.com/search?hl=en&lr=&ie=ISO-8859-1&q=synapses+growth+begins+fetus |
Request for Answer Clarification by
brunews-ga
on
14 Sep 2002 21:33 PDT
Thank you Websearcher.
Looks like you are right: I have followed all your links, some of them
very interesting and kept for further reading, but the only graph
around seems to be:
the figure labeled "The Brain: Synaptic Pruning".
by Stubasaki and Miyazaki, 1992 (research on those names doesn't lead
very far.)
I must say that I am a little confused: I thought that this kind of
graph would be available, at least in a corner somewhere. Now we have
a graph, found at least in 2 documents where it is shown totally out
of context, as proof for a vague notion of some activity in the brain.
No number used in the graph is explained or discussed.
If we can't find a better graph, at least we can try to understand
this one:
1- Synapses/mm(3) x 10(8)
facing a scale: 5, 10, 15, 20
It's a measurement of volume, which can't be related to a number of
synapses.
2- NB seems to mean: age
3- Synapse count
OK
4- Amplitude of visual Me
is a mystery to me
5- I don't understand what the scale on the right is about.
Any idea?
As for "putting something interesting together", thank you: I am just
trying to understand the dynamics of the web; I look for different
mapping systems in a variety of related fields. An it turns out that
it's not as easy as I thought first. ;-)
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Clarification of Answer by
websearcher-ga
on
15 Sep 2002 07:10 PDT
Hi brunews:
I will fully admit I share your confusion about the lack of other
graphs of this phenomenon. I also thought there would be more of them
available on the Web....
Let's look at the graph we do have and try to explain the various
parts of it.
1- Synapses/mm(3) x 10(8)
facing a scale: 5, 10, 15, 20
Yes, as you point out, this is a volume related measurement, plotting
the number (in units of 100,000,000) of synapses per square millimeter
of brain tissue versus age. While this does not immediately provide
the total number of synapses, it does provide for a good
representation of how that total varies with age. All the supporting
literature that I found supports this.
Since brain volume itself increases dramatically during the first two
years of life, then continues to grow but more slowly during the rest
of childhood, and stops growing altogether (even decreasing) during
adulthood, the overall number of synapses would provide a similar
looking graph (with similar peaks and angles).
2- NB seems to mean: age
Actually, I'm pretty certain that NB represents "NewBorn" and that
they have simply neglected to label the horizontal axis as "age".
4- Amplitude of visual Me
is a mystery to me
If you use the magnifying glass feature of your browser's PDF viewer
to enlarge the figure, you'll see that this actualy reads "Amplitude
of visual Nc".
This stands for "Amplitude of visual neocortex". The neocortex is...
"the structure in the brain that differentiates mammals from other
vertebrates and it is assumed that the neocortex is responsible for
the evolution of intelligence"
From: http://serendip.brynmawr.edu/bb/kinser/Int6_neo.html
It is believed that measuring the amplitude (size) of the brainwaves
in the visual neocortex is a good measure of overall brain efficiency,
or maturation. The following page provided the "simplest" explanation
of this I could find - although it is still rather "deep".
Long-Term Potentiation (LTP)
http://www.psych.ucalgary.ca/CourseNotes/old/PSYC476/LTP.html
As you can see, the values for the amplitude (the triangular symbols)
match up almost prefectly with the synapses count function - verifying
that they are related.
5- I don't understand what the scale on the right is about.
The scale on the right is meant for the "Amplitude of the visual Nc"
symbols. Often, when someone wants to plot two functions with
differing scales on the same plot, they will use one scale on the left
(in this case, the number of synapses) and another scale on the right
(in this case, the amplitude of the visual neocortex). While this is
tricky to read, once you get the hang of it, it's not so bad. For
example, at age 5 (if you find the triangular symbol above 5 on the
horizontal azis and read over to the right), the value for amplitude
would be about 32.
I believe the label on the righthand scale refers to "neocortex
micro-volts at the fronto-central electrode", which basically means
"the amplitude measured in very small units at the front of the
brain". I found some of these same symbols in a paper here:
"The MMN amplitude increases in hypnosis: a Case Study"
http://users.utu.fi/shakal/LMMN%20and%20hypnosis.pdf
I hope this clears some things up for you and enables you to continue
your web dynamics work.
websearcher-ga
Search Strategy:
neocortex
://www.google.com/search?hl=en&lr=&ie=ISO-8859-1&q=neocortex+
neocortex amplitude growth
://www.google.com/search?hl=en&lr=&ie=ISO-8859-1&q=neocortex+amplitude+growth
fz amplitude
://www.google.com/search?hl=en&lr=&ie=ISO-8859-1&q=fz+amplitude
|
Request for Answer Clarification by
brunews-ga
on
20 Sep 2002 11:34 PDT
This is not a "Request for Answer Clarification". This would be more
like a comment, but not other place is available.
So: thank you very much Websearcher, I award you the top count of
stars as a researcher: you have found and explained everything I could
verify that is available on Google.
My point is more a point for Google and Google Answers: the
information I am looking for is around somewhere, as shown by the
crappy graph found by Websearcher.
How come Google doesn't have access to scientific information which is
somewhere around, I am sure on several files and studies? Why Google
doesn't have access to Internet 2, perhaps as a read-only fonction?
Or: how come no scientific researcher who may have access to this kind
of information is available for or even aware of Google Answers?
My question, and others I have in my sleeves, show a huge hole at the
center of available knowledge on the web: a huge hole in Google reach.
I must say I am disappointed with Google Answers and will pursue my
reaserch the old fashion way: one scientist at a time. :)
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