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

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 🙂

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5 Responses

  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.

  2. Alvaro says:

    Hello Predman, very good point. Yes, it depends on the definition of “connections”

  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. ( 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. 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.

  5. […] Your brain is a truly impressive piece of hardware. It has about 100 billion neurons, with as many synaptic connections as there are leaves in the Amazon Rainforest. […]

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