Humans have about 86 billion neurons
Fact

Humans have about 86 billion neurons on average.

How Many Neurons Does the Average Human Have?

Studies show the average human has about 86 billion neurons and roughly as many glial cells, however the exact number of neurons and glial cells remains unknown.

The 100 Billion Neuron Myth

Humans have about 86 billion neurons, not 100 billion.

It turns out the long-cited “100 billion and 10 more glial cells” line is junk science and lacks citation to any peer-reviewed study. Only one real study has been done on neuron counts, and that study showed the average male has about 86 billion neurons (+/- 8.1 billion) and 84.6 (+/- 9.8 billion) non-neuronal cells (glial cells). No study has ever shown 100 billion, although a study was done that myth-bused the 100 billion neuron claim and backed up the 86 billion neuron claim. With this in mind, the best we can do is give a rough estimate when teaching or writing. The exact number of neurons in the average human won’t be known without further studies to confirm the one singular study done. [1] [2]

86 billion neurons

The average human brain has 86 billion neurons.

86 Billion, Not 100 Billion Neurons (According to Peer-Reviewed Studies)

Here is an excerpt from the 2009 study mentioned above that shows the average human male has about 86.1 (plus or minus 8.1) billion neurons (not 100 billion):

“We find that the adult male human brain contains on average 86.1 +/- 8.1 billion NeuN-positive cells (“neurons”) and 84.6 +/- 9.8 billion NeuN-negative (“nonneuronal”) cells.” – Equal numbers of neuronal and nonneuronal cells make the human brain an isometrically scaled-up primate brain.

Here is an excerpt from the study that pointed out that the 100 billion neurons myth had persisted despite no one ever actually knowing the count before the 2009 findings:

How many neurons does the human brain have, and how does that compare to other species? Many original articles, reviews and textbooks affirm that we have 100 billion neurons and 10 times more glial cells (Kandel et al., 2000; Ullian et al., 2001; Doetsch, 2003; Nishiyama et al., 2005; Noctor et al., 2007; Allen and Barres, 2009), usually with no references cited. This leaves the reader with the impression that the cellular composition of the human brain has long been determined. Indeed, an informal survey with senior neuroscientists that we ran in 2007 showed that most believed that the number of cells in the human brain was indeed already known: that we have about 100 billion neurons, outnumbered by about 10 times more glial cells – but none of the consulted scientists could cite an original reference for these numbers (Herculano-Houzel and Lent, unpublished observations). – The Human Brain in Numbers: A Linearly Scaled-up Primate Brain.

Revising the numbers. How researchers got to a figure of 86 billion neurons, instead of the 100 billions previously estimated. 

FACT: For comparison a jellyfish has about 5.6 thousand neurons, a cockroach has about 1 million, a house mouse has about 71 million, a squirrel monkey about 3.24 billion, and an African elephant 267 billion. [3]

NOTE: Interestingly, the study that found the count of neurons also makes a comment on evolution: “This is the same ratio found in primates. These findings challenge the conventional view that humans stand out from other primates in their brain composition and indicate that, about numbers of neuronal and nonneuronal cells, the human brain is an isometrically scaled-up primate brain.”

Do We Grow New Neurons? Is That Why the Old Count Was Off?

Some parts of the brain contain neural stem cells. These stem cells continue to grow new neurons. The more you use the parts of your brain that contain these cells, the more new cells are produced. Despite this number of neurons a person has doesn’t change much from birth, although you can grow more neurons in certain parts of the brain, so it is unlikely this is the source of the number being off. [4]

TED Talks explains how you can grow new brain cells (neurons).

What are Neurons?

Neurons (or nerve cells) are “electrically excitable cells” that process and transmit information through electrical and chemical signals over synapses. Neurons are one of the main core components of the brain; they can also be found in the spinal cord, central nervous system, and throughout the body.

Each neuron connects to other neurons and cells via up to as many as 5,000 – 10,000 synapses creating a “neural network” of sensory information. [5]

Neurons are the brain cells where we store our sensory memories and are a big part of what makes us “us”. Our brains are constantly “rewiring” changing how we view the world.

A video explaining neurons in two minutes or less.

FACT: Synapses don’t just connect neurons to each other; they connect them to 1,000-10,000 other neurons, muscle cells, glands, etc.[6]

What are Glial Cells?

Glial cells are the supporter cells of neurons.

How Do We Store Information in Neurons?

When we perceive sensory input we store it as memories in our neurons (blips of sensory information, connected to through synapses, that our brain makes sense of through memory recall).

Each neuron is designed (via it’s DNA) to encode a different type of sensory information, so each of the many neuron types will be primed to store a particular type of sensory information.

When two neurons receive information at the same time, they connect to each other via synapses forming or strengthening “synaptic connections”. These synaptic connections between neurons form complex neural networks. These systems act as pathways associating bits of sensory information together to recall as needed.

How Do We Retrieve Information From Neurons?

When we recall a memory, we are grabbing sensory information from many different synaptically connected neurons. The brain pieces this information together to repaint a picture one sensory memory at a time. In other words, memories aren’t just one thing, but rather it’s many neurons and their connections that “store” a single memory.

It’s all in the Nervous System

Neurons relate to many different types of sensory memories, and there are many different types of neurons throughout our bodies’ nervous system. All of our memories, creativity, thought, ideas, abilities, and most of who we are “stems” from information stored in our neurons and the X trillion synaptic connections between them.



Notes

Authors Notes on 100 Billion versus 86 Billion Plus or Minus 8.

As I was studying neurons in relation to other subjects like memory I ran across the numbers 86 and 100 billion almost interchangeably when discussing the average number of neurons a human has.

Upon research I realized that some sources were using this study: “Equal numbers of neuronal and nonneuronal cells make the human brain an isometrically scaled-up primate brain” While the 100 billion average camp was likely rounding up.

I originally titled the page “100 billion neurons” and rated it a myth, but ultimately I thought that was confusing as it wasn’t “common knowledge”.



The page now reads “the average human has 86 billion neurons on average” and is rated a fact to avoid confusion.


Conclusion

Humans have about 86 billion neurons, not 100 billion. Being off by 15 billion neurons is significant. Remember neurons aren’t just in the brain, we have neurons throughout our entire bodies.


Citations

  1. The Human Brain in Numbers: A Linearly Scaled-up Primate Brain” ncbi.nlm.NIH.gov
  2. Equal numbers of neuronal and nonneuronal cells make the human brain an isometrically scaled-up primate brain.” ncbi.nlm.NIH.gov
  3. List of animals by number of neurons” Wikipedia.org
  4. How to Grow New Neurons in Your Brain” Psychologytoday.com
  5. Department of Brain and Cognitive Sciences” web.MIT.edu
  6. Brain Cells” Enchantedlearning.com


"Humans Have About 86 Billion Neurons" is tagged with: Cells, Collective Intelligence, Human Brain, Memory, Neurons, Systems


Vote Fact or Myth: "Humans Have About 86 Billion Neurons"

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Rohit Kanade on

humans have 100 billion neurons

Thomas DeMichele
Thomas DeMichele on

No, i was confused by this and tis why I created the page. The studies all show that 100 billion neurons is some estimate given in a TED talk and the actual number is 86+- as presented above. That said, more studying is needed.

If you disagree, please drop a citation, peer-reviewed citation ideally since we are talking about counting neurons.

Rohit Kanade on

I have a question
what is the difference between 86 and 100?

Thomas DeMichele
Thomas DeMichele on

Well it is 86 billion neurons +/- (plus or minus) 8.1 billion. So it is between 78 billion and 94 billion. Thus, the difference is as many as 22 billion neurons.

If I offer you $100 and give you $75, you’ll probably ask for the other $25. If I give you $94, maybe you’ll let it slide. Those numbers are closer.

Point being, rounding 86 billion neurons (+/- 8.1 billion) and 84.6 (+/- 9.8 billion) non-neuronal cells (glial cells) (for a total of very roughly 180 billion brain cells) to 100 billion neurons, is too rough of an estimate. Better to say, “according to studies about 85 billion plus or minus a few billion neurons”… or just “roughly 85 billion neurons according to one study” something like that.

I’m not an expert or the end-all-be-all here, just researched the “100 million neurons claim after hearing it a few times” then found this: //www.ncbi.nlm.nih.gov/pmc/articles/PMC2776484/

That study explains their own research. In their research they discovered everyone was just parroting the 100 million number without citations up until their 2009 report.

All this to say, not a big deal in general, and I’d think more studies should be done, but if we want to be accurate, this is the data. Pull from it what you will.

Rohit Kanade on

Isn’t it a little difference?