Even if Herculano-Houzel's method somehow skews the ratio too close to 1:1, the evidence as a whole certainly does not support anything near a 10:1 ratio. And some scientists who study glia are reluctant to admit that these once overlooked cells might not constitute the majority. Some researchers, however, will not fully accept the new method until Herculano-Houzel directly compares it to more traditional cell-counting techniques. The most compelling evidence for a 1:1 ratio comes from a 2009 study by neurophysiologist Suzana Herculano-Houzel and her colleagues, who invented a new, highly efficient way to count cells and applied it to four whole human brains. We found many studies from as early as the 1950s that settled on a ratio much closer to 1:1 in the brains of humans and other primates, although most of these studies focused solely on the intricately wrinkled outer layer of the vertebrate brain, known as the cortex, which probably does not have the same glia to neuron ratio as the rest of the brain. If anyone knows of such a study, please cite it in the comments section. We decided to investigate further.Īfter surveying the research literature, we did not find a single published study that directly supports a 10:1 glia to neuron ratio in the whole human brain.

Noah Gray a senior editor at Nature, and Mo Costandi a neuroscientist turned freelance writer, responded to our post on Twitter, citing recent evidence that the 10:1 glia to neuron ratio is a myth and that the ratio in human and other primate brains is much closer to 1:1. Glia 'outnumber neurons by as much as 50 to one,' we wrote, echoing Eric Kandel's widely used textbook, The Principles of Neural Science, which states: 'Glial cells far outnumber neurons-there are between 10 and 50 times more glia than neurons in the central nervous system of vertebrates.' Other textbooks, including Mark Bear's Neuroscience-Exploring the Brain, make similar claims, as have many articles in the popular press. Last time on Know Your Neurons, we talked about glia-one of two major types of cells in the brain and nervous system alongside neurons. Chapter 1: The Discovery and Naming of the NeuronĬhapter 2: How to Classify Different Types of NeuronsĬhapter 4: What is the Ratio of Glia to Neurons in the Brain?

How many neurons in the human brain