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> How Many Synapses in the Human Brain?
GodConsciousness
post Jun 19, 2009, 06:01 AM
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Figures seem to vary widely up to 500 trillion
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lucid_dream
post Jun 19, 2009, 07:47 PM
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100 trillion (10^14) is what I've heard, assuming 10 billion neurons (10^10), each having an average of 10,000 synapses.

the methods for computation rely on statistical sampling, which are liable to large errors. Even saying the figures computed for total synapses in the human brain using statistical sampling fall within a "ballpark" range is probably too optimistic. IMHO, nothing short of a comprehensive mapping (and counting) will offer a satisfactory answer.

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GodConsciousness
post Jun 20, 2009, 03:22 AM
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Hopefully you can elucidate this further in your work LD. Just shows how ambitious a project mapping every synapse really is!
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Phi
post Jun 20, 2009, 04:38 AM
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at that point, it seems pointless to compare the amounts. Utilization seems more productive....

All i know is that theres a shitload, so try to make the best out of what you have....and it seems like a great selection
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maximus242
post Jun 20, 2009, 09:02 PM
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Could probably come up with some kind of synapse imaging technology using nanotechnology based sensors along with computational algorithms to figure it out. Use molecular properties of the synapse to trigger a molecular sensor, kind of like how supramolecular chemistry works and then use that to send a count signal to a "counter" maybe like a modified DNA string, then mark the synapse in some way to avoid it from being counted again.

Things are a little tricky on the nanoscale for computation, but its doable for something so simple. Then processing the information you could even just have multiple counters, thousands or millions of things that keep the count and billions of "counting" molecules. Then simply extract the counter molecules and run some kind of machine that detects the number of a counting molecule. Basically you could just use amino acids for the counting molecule and instead of having it for genetic code, use it for computation.

Theres been some work on modifying DNA like that for computation.
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Hey Hey
post Jun 21, 2009, 03:45 PM
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I wonder what the variability is? And the male-female differences? And the change with age? But accuracy could be quite important to make any sense of the differences.
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astroidea
post Jun 26, 2009, 05:34 PM
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Also, don't forget that in the number of synapses will vary by 35-50% in a sleep wake cycle.

As you are awake in the day, you build synapses as you interact with your environment and experience.
In the night, sleep prunes away those synapses via slow wave activity, to refresh them back to a baseline state after every full sleep. Only a small trace of the synapses are left to retain memory. This helps save energy and creates space for new synapses to be formed.
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kortikal
post Jun 28, 2009, 10:53 PM
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QUOTE(astroidea @ Jun 26, 2009, 06:34 PM) *

Also, don't forget that in the number of synapses will vary by 35-50% in a sleep wake cycle.

As you are awake in the day, you build synapses as you interact with your environment and experience.
In the night, sleep prunes away those synapses via slow wave activity, to refresh them back to a baseline state after every full sleep. Only a small trace of the synapses are left to retain memory. This helps save energy and creates space for new synapses to be formed.


Source?
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astroidea
post Sep 27, 2009, 05:20 PM
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QUOTE(kortikal @ Jun 28, 2009, 11:53 PM) *

QUOTE(astroidea @ Jun 26, 2009, 06:34 PM) *

Also, don't forget that in the number of synapses will vary by 35-50% in a sleep wake cycle.

As you are awake in the day, you build synapses as you interact with your environment and experience.
In the night, sleep prunes away those synapses via slow wave activity, to refresh them back to a baseline state after every full sleep. Only a small trace of the synapses are left to retain memory. This helps save energy and creates space for new synapses to be formed.


Source?


Sorry for the late response, haven't checked this thread in a while
http://www.ncbi.nlm.nih.gov/pubmed/16376591
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lucid_dream
post Sep 28, 2009, 06:42 AM
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great, but that reference does not claim that number of synapses varies by 30-50%, only that synaptic strength varies.
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astroidea
post Sep 29, 2009, 01:50 AM
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QUOTE(lucid_dream @ Sep 28, 2009, 07:42 AM) *

great, but that reference does not claim that number of synapses varies by 30-50%, only that synaptic strength varies.

I stand corrected.
I misunderstood what synpatic weight was when reading the article, which I thought was due to both quantity and strength. I feel a bit sheepish now presenting that to my class. My TA didn't catch me on that.

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GodConsciousness
post Dec 20, 2010, 07:55 AM
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Finally getting around to reading "The Synaptic Organization of the Brain" (awesome book by the way!!) and Shepherd says that there are somewhere in the neighborhood of 60 trillion synapses in the human cortex. Not sure if Shepherd revises this estimate in the latest Microcircuit book and I know we are working with extremely rough estimates here and a precise mapping will be the only way to get precise numbers, but it is interesting how much variation there is in sampling estimates.
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