In early June, the Global Brain Health Institute hosted Suzana Herculano-Houzel, a Brazilian scientist who challenged the dogma that the brain has a hundred billion neurons. Herculano-Houzel could find no evidence or origin for this claim, so she set out to count every neuron herself. Her book The Human Advantage chronicles her journey into the brain to prove that humans fall short of this number. In the end, she found that the human brain has 86 billion neurons, far fewer than other species with bigger brains. Her message: humans aren’t as special as we think we are.
Herculano-Houzel is an amazing writer and speaker, and she has become a rock star in the neuroscience world. She moved to the United States a few years ago to continue her work at Vanderbilt University, but she spent much of her career in her home country (and mine) of Brazil. One night during her visit to the UCSF Memory and Aging Center, she shared a small stage with UCSF’s Bruce Miller and Lea Grinberg to talk about creativity and perseverance—what it takes to develop new ideas, how to prove them, and how to produce high-quality research with scarce resources. She stressed that the key is to ask difficult questions, particularly ones that others shy away from, and devise creative ways to answer them.
It was Herculano-Houzel’s relationship with Grinberg, who helped to create the first brain bank in Brazil, that allowed her to answer the human neuron number puzzle. The two women talked about the challenges young female scientists in developing countries face, including language, limited financial support, building trust in the scientific community, and the lack of government infrastructure and commitment to science. Herculano-Houzel advised the audience: “Follow your dreams. Do not give up against obstacles imposed by bureaucracy, prejudice, and controversy.”
These two strong and creative women scientists paved a path for other women to follow, and I resonated with their stories. Hearing them speak, I felt that I could return to Brazil and build my own roads to help people in my community understand the brain (and the rest of the body) and learn how to reduce their risks for brain diseases.
Herculano-Houzel’s visit to UCSF culminated in a riveting talk to a packed house of scientists, doctors, and other health professionals. She revealed the secret to counting billions of neurons (“brain soup”), compared the brain size of humans to other mammals in relationship to body size, and discussed what brain size might tell us about what it means to be a human, or a chimpanzee, or a mouse, or an elephant. For instance, the elephant brain has three times more neurons than the human brain, but virtually all of the elephant’s neurons—98 percent of them—are in the cerebellum. The human brain, by comparison, houses most of its neurons in the cerebral cortex.
So how did the human brain accumulate so many neurons in the cortex? Herculano-Houzel believes that it is because our ancestors learned how to cook. The brain consumes 25 percent of the body’s energy. If we wanted bigger brains the old fashioned way, we would have to eat for eight hours every day to feed our brains with the calories they need to support the additional cells. However, by processing food with tools and fire, it became possible to acquire more calories with less effort. This allowed our ancestral Homo to increase the numbers of neurons in the cortex, possibly allowing us to develop special abilities, such as language and the production of art.
Cooking was the key step in human evolution that made us different from other animals and enabled us to dominate them, build civilizations, and develop technologies. The result is that we live longer, but now we face a new set of problems as our body and brain have not evolved at the same speed as the advances in medicine. What will be the next crucial evolutionary step to overcome the disadvantages gained with our advantageous human brain? Can we protect our brain from neurodegeneration by building up its cognitive reserves and enhancing its connections and flexibility with more environmental stimuli?
Herculano-Houzel’s lessons will not be wasted on this audience. We learned that it is crucial to develop and diversify our research tools to understand brain aging and neurodegenerative diseases. We cannot be content with accepting previous theories and assumptions. We need to let our instincts flow, our creativity rise, and we need to think outside of the box when it comes to the brain diseases that we want to treat or prevent. Her optimism inspired us to ask and answer the tough questions, and we will face the dementia epidemic with the same creativity and rigor that she has given to counting neurons.
The author thanks Jamie Talan for reviewing the English.