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Approximately how many neurons and neural connections are there in the mature human brain?

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William Delaney | (Level 1) Distinguished Educator

Posted March 9, 2013 at 3:42 AM via web

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Approximately how many neurons and neural connections are there in the mature human brain?

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belarafon | High School Teacher | (Level 2) Educator Emeritus

Posted March 10, 2013 at 5:49 PM (Answer #1)

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The number of neurons in the human brain has long been estimated at about 100 billion, with neural connections -- synapses -- placed at about 100 trillion. However, these estimates have been proved to be baseless; researchers have shown that there is no proper research behind the 100 billion estimate, and it is simply a statistic of convenience, repeated until taken at face value. A 2009 study by Azevedo et al. showed that the male human brain at around the age of 50 contains around 86.1 ± 8.1 billion neurons, fewer than the accepted estimate and closer to that of a standard primate brain. This study was only based on the brains of adult males, so the number of neurons across the mature adult human spectrum could vary; the acceptable error of ± 8.1 billion is a safe estimate for other human brains, so the actual number could be anywhere from 78 - 94 billion. As for synapses, a single neuron can have up to a thousand synapses, making this number much harder to estimate; based on the new number of about 86 billion neurons, the brain might have up to 0.15 quadrillion synapses. The most important aspect of this research is that it shows the human brain to be less-different from standard primate brains than originally assumed; while the human brain contains more neurons than a primate brain, it is only on an isometric scale, meaning that the human brain is remarkable more in its size than in its composition.

 

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William Delaney | (Level 1) Distinguished Educator

Posted March 10, 2013 at 10:26 PM (Answer #2)

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The number of neurons in the human brain has long been estimated at about 100 billion, with neural connections -- synapses -- placed at about 100 trillion. However, these estimates have been proved to be baseless; researchers have shown that there is no proper research behind the 100 billion estimate, and it is simply a statistic of convenience, repeated until taken at face value. A 2009 study by Azevedo et al. showed that the male human brain at around the age of 50 contains around 86.1 ± 8.1 billion neurons, fewer than the accepted estimate and closer to that of a standard primate brain. This study was only based on the brains of adult males, so the number of neurons across the mature adult human spectrum could vary; the acceptable error of ± 8.1 billion is a safe estimate for other human brains, so the actual number could be anywhere from 78 - 94 billion. As for synapses, a single neuron can have up to a thousand synapses, making this number much harder to estimate; based on the new number of about 86 billion neurons, the brain might have up to 0.15 quadrillion synapses. The most important aspect of this research is that it shows the human brain to be less-different from standard primate brains than originally assumed; while the human brain contains more neurons than a primate brain, it is only on an isometric scale, meaning that the human brain is remarkable more in its size than in its composition.

 

Thank you very much. I appreciate this up-to-date information.

 

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