The National Numeracy Network > Numerous Neurons

Numerous Neurons

Nathan Grawe
published Nov 12, 2013

The current (Nov 7, 2014) issue of Nature is all about recent science surrounding the human brain. One interesting tidbit I picked up is that our current best guess is that the human brain includes 86 billion neurons.

Now, that's a pretty big number. But just how big is it? I poked around Nature's website and found this interesting blog that gave me an answer. Author Bradley Voytek notes that the most common comparison is that "there are as many neurons in the human brain as there are stars in the Milky Way." But Voytek tells us that this isn't quite right--our best guess for stars in the Milky Way is between 200 and 400 billion.

He also shares some details about how we estimate the number of neurons. (Turns out counting one by one isn't a good strategy--who knew?!) Problems abound. The brain isn't uniformly dense with neurons, so sampling matters. And the neurons are so intertwined that the current best estimate comes from a strategy of disolving brain samples and introducing a dye that sticks to the nuclei of neurons. All in all, a pretty interesting example for teaching ideas of representative sampling and estimation techniques. An interesting problem to which your students can apply a few of those neurons!

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