#4. Guess: Are there more brain connections in one human brain or leaves in the whole Amazon?

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neural connections

QUESTION: How many neu­rons does your brain have, and how many con­nec­tions can each neu­ron have? Then, how many total brain con­nec­tions are there in your brain…and how many leaves in the whole Amazon?

ANSWER: Your brain is made up of around 100 bil­lion neu­rons — about the same as the num­ber of trees in the Ama­zon rain­for­est. And each neu­ron is con­nect­ed to around 10,000 oth­ers. So the total num­ber of con­nec­tions in your brain is about the same as the num­ber of leaves in the rain­for­est — about 1,000 tril­lion. Yes, a quadrillion, to make some sharp com­menters below happy 🙂

Next brain teas­er in Sharp­Brains’ top 25 series:

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  1. Predman says

    Each nerve cell is direct­ly con­nect­ed to 10,000 oth­er nerve cells? Because all the pic­tures of nerve cells only show 5–10 con­nec­tions com­ing in and out… Maybe they mean “con­nec­tion” like the con­nec­tion between NY and LA — thru Cleve­land, Indi­anapo­lis, St. Louis, Den­ver and oth­er nerve cells along the way.

    So the answer to the ques­tion would then be a ques­tion of inter­pre­ta­tion. If you go with “direct con­nec­tions” then there are more leaves in the Amazon…

    The link is a 404, btw.

  3. gil says

    Hi Pred­man and Alvaro-
    Actu­al­ly you should­n’t be fooled by the sim­plis­tic dia­gram­mat­ic appear­ance used to por­tray brain neu­rons. These images are often cre­at­ed by inject­ing cells with floures­cent mark­ers that allow us to see a sin­gle cell. What we don’t see are the count­less divi­sions occur­ring as the den­drites spread out from the cell (like infi­nite­ly divid­ing branch­es on a tree) and oth­er nerve den­drites attached at var­i­ous points to that cell, like count­less leaves from oth­er trees inter­twined with and attached at thou­sands of points to our ‘tree’. I think that wike­pe­dia does a good job of describ­ing neu­ro­log­ic synaps­es and clear­ly states the total num­ber of synaps­es in our brains is between 100 and 500 tril­lion. (http://en.wikipedia.org/wiki/Synapse). This would trans­late to 1 to 5 thou­sand synaps­es per neu­ron and is more in keep­ing with the num­ber of leaves on an Ama­zon tree.

  4. Alvaro Fernandez says

    Gil, thank you for the addi­tion­al context.

    Indeed, Mar­i­an Dia­mond did a great job when she titled her clas­sic book Mag­ic Trees of the Mind.