How Many Neurons in Your Brain?

Homer Simpson's brain may contain fewer brain cells or neurons than the average cartoon character's (except maybe SpongeBob SquarePants - sponges don't have brains). But the question remains - what is the average number of neurons in the human brain? Now a new study, led by neuroscientist Dr. Suzana Herculan-Houzel from Brazil, has found out.

Houzel and her team of researchers used some nasty sounding techniques to determine the number of neuronal cells in the brain. Using four brains from individuals who donated their organs to science, the scientists turned the brain tissue in to a "brain soup". They then dissolved the cell membranes, therefore mixing up all the nuclei. They then sampled the soup, counted the number of neuronal nuclei, scaled up the figure and hey presto! 

So what is the average number of cells in the brain? Well, the brain consists of neurons and other cells called neuroglia or just glia (these glial cells help maintain homeostasis, form the insulating myelin, and provide support and protection for neurons in the brain - they include Schwann cells which you might have heard about). The researchers found that, on average, there are 86 billion neurons and 84 billion glial cells in the brain. This is far less than originally thought, with many scientist estimating the figure was closer to 100 billion.

The researchers also found that the ratio between glial cells and neurons in the human brain structures are similar to those found in other primates, and their numbers of cells match those expected for a primate of human proportions. The findings challenge the common view that humans stand out from other primates in their brain composition and indicate that, with regard to numbers of neuronal and glial cells, the human brain is just a scaled-up primate brain.

The research is published in Journal of Comparative Neurology.

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