# What is so special about the human brain?



## David Baxter PhD (Nov 26, 2013)

*Suzana Herculano-Houzel: What is so special about the human brain?*
TED Talks
June 2013

 						The human brain is puzzling -- it is curiously large given the  size of our bodies, uses a tremendous amount of energy for its weight  and has a bizarrely dense cerebral cortex. But: why? Neuroscientist  Suzana Herculano-Houzel puts on her detective's cap and leads us through  this mystery. By making "brain soup," she arrives at a startling  conclusion. 					


 											 							Suzana Herculano-Houzel shrunk the human brain by 14 billion neurons -- by developing a new way to count them.



How many neurons make a human brain? For years, the answer has been  (give or take) 100 billion. But neuroscientist Suzana Herculano-Houzel  decided to count them herself. Her research approach involved dissolving  four human brains (donated to science) into a homogeneous mixture -- in  her lab at the Institute of Biomedical Sciences in Rio de Janeiro, they  call it "brain soup." She then took a sample of the mix, counted the  number of cell nuclei belonging to neurons, and scaled that up. Result:  the human brain has about 86 billion neurons, 14 billion fewer than  assumed -- but intriguingly, far more than other animals, relative to  brain size.


  She suggests that it was the invention of cooking by  our ancestors -- which makes food yield much more metabolic energy --  that allowed humans to develop the largest primate brain. She's now  working on elephant and whale brains to test her hypothesis.


----------



## David Baxter PhD (Nov 26, 2013)

*Lessons from brain soup: Suzana Herculano-Houzel at TEDGlobal 2013*
by Kate Torgovnick 
June 12, 2013



 For decades, scientists said that the human brain contains 100  billion neurons. However, when neuroscientist Suzana Herculano-Houzel  hunted for the source of this often-quoted number, she couldn’t locate  one. So she set out to count herself … by making brain soup.

 She brings a vial of brain soup with her onto the TEDGlobal 2013  stage. This substance was made by dissolving donated brains, destroying  the cell membranes but leaving the nuclei intact. This made a homogenous  mixture that allowed her to count the neurons in a sample. As it turns  out, the human brain really has 86 billion neurons.

 Why does this difference of 14 billion neurons matter? It answers a  vital question: What makes the human brain different, allowing us to get  together for thought-fests like TEDGlobal 2013, while other animals  don’t?

 For a long time, scientists thought that all mammal brains were made  of the same material. But if that were true, then mammals with larger  brains would be the most cognitively able. That simply isn’t true. Plus,  human brains reveal a few oddities. For instance, Herculano-Houzel  says, we have a larger cerebral cortex than it seems like we should  have, given the size of our bodies. Meanwhile, human brains use a  tremendous amount of energy. While the brain is 2% of the body, it uses  25% of the calories we need to function each day. Why should the rules  of evolution not apply to humans?

 This brings us back to Herculano-Houzel’s finding that the human  brain actually contains 86 billion neurons. The new baseline allowed her  lab to do comparisons to other animal brains. And they found that human  brains are proportional in terms of the number of neurons and energy  use to other primate brains — they are just larger. “It’s a great  reminder of our place in evolution,” says Herculano-Houzel.

 Which still leaves the question: Why would we have a larger brain  than a great ape that has a much larger body? The answer comes down to  the extreme energy cost of the primate brain. There appears to be some  kind of evolutionary trade-off between the size of the brain and the  size of the body — there’s a metabolic limitation, and primates can only  consume enough calories to support one or the other.

 So the next logical question is: What allowed us to transcend this  limitation and support this large brain? Herculano-Houzel points out  that our cerebral cortex is especially dense, containing 16 billion  neurons. It takes a lot of energy to support that.



 The answer is so simple, it’s something you’ve probably never thought  about. Herculano-Houzel states it in two words: We cook. Cooking is  essentially the act of using fire to pre-digest food, and thus to get  more energy out of the same amount of food. In fact, cooking food makes  it yield about three times as many calories. This is what allowed our  brains to get bigger in a relatively short period of time while  remaining a primate brain. Cooking also allowed us to support this large  cerebral cortex, which in turn supports complex thought.

 Wrapping it all up, Herculano-Houzel concludes, “I take a look at my kitchen, and I bow down to it.”

 She’ll just maybe skip the soup.


----------



## David Baxter PhD (Nov 27, 2013)




----------

