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How Many Neurons Are in the Brain?

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How Many Neurons Are in the Brain? Image by Mark Miller (CC BY-SA 2.0)
Question: How Many Neurons Are in the Brain?
Answer: The human brain is made up of a complex network of neurons. These neurons serve as the building blocks of the nervous system, transmitting information to and from the brain and throughout the body. Just how many neurons are there in the human brain?

How Many Neurons are in the Human Brain?

According to most sources, the human brain contains around 100 billion neurons (give or take a few billion).

This estimate has been often reported for many years in neuroscience and psychology textbooks. Recently, however, Brazilian researcher Dr. Suzana Herculano-Houzel discovered that these estimates might not be entirely accurate. While the number is widely cited, she found that no one seemed to know where this number originated. She then decided to investigate in order to determine if the number is accurate. Researchers used a method that involves dissolving the cell membranes in order to create a sort of "brain soup" so that they can then count the number of cell nuclei.

How many neurons did the researchers find in the brains they analyzed?

"We found that on average the human brain has 86bn neurons. And not one that we looked at so far has the 100bn. Even though it may sound like a small difference the 14bn neurons amount to pretty much the number of neurons that a baboon brain has or almost half the number of neurons in the gorilla brain. So that's a pretty large difference actually," explained Herculano-Houzel.

So, according to this new research, the human brain likely has somewhere around 85 billion neurons.

Neurons in Other Animals

According to Herculano-Houzel, human brains are remarkably similar to primate brains with one important distinction: we have far more brain cells that require a tremendous amount of energy to fuel and maintain. Experts suggest that an estimated 25 percent of all our energy expenditure goes toward fueling these cells.

The sheer number of neurons present in the human brain becomes more apparent when compared to other species. So how many neurons are in the brains of other animals?

  • Fruit Fly: 100 thousand neurons
  • Cockroach: One million neurons
  • Mouse: 75 million neurons
  • Cat: One billion neurons
  • Chimpanzee: 7 billion neurons
  • Elephant: 23 billion neurons

Learn more about neurons and the human brain:

References

Herculano-Houzel S (2009). The human brain in numbers: A linearly scaled-up primate brain. Frontiers in Human Neuroscience, 3(31). doi:10.3389/neuro.09.031.2009

Orca, S. (2009, Nov 30). The race to reverse engineer the human brain. H + Magazine. Retrieved from http://hplusmagazine.com/2009/11/30/race-reverse-engineer-human-brain/

Randerson, J. (2012, Feb 28). How many neurons make a human brain? Billions fewer than we thought. The Guardian. Retrieved from http://www.guardian.co.uk/science/blog/2012/feb/28/how-many-neurons-human-brain

Williams, Robert W. (2000). "Mapping Genes that Modulate Mouse Brain Development: A Quantitative Genetic Approach". In: Mouse brain development (Goffinet AF, Rakic P, eds), Springer Verlag, New York, pp 21–49.

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