Suzana Herculano-Houzel: What is so special about the

human brain?

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.

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

Why you should listen to her:

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.

"It took me a couple of months to make peace with this idea that I was going to take somebody's brain or an animal's brain and turn it into soup. ... It's really just one more method that's not any worse than just chopping your brain into little pieces."