Who Counted All The Neurons? – Exploring Cognitive Science 🧠

We've all heard it before: 100 billion neurons make up our brain. Is that really true? And who counted all the neurons anyway?
Today on “Exploring Cognitive Science”, we discover the story of Suzana Herculano-Houzel's "isotropic fractionator".

For decades, textbooks repeated the estimate of 100 billion neurons, based on indirect and inconsistent measurement methods. In this video, we explore how scientists have tried to count brain cells using histology techniques, sampling tissue slices under the microscope, and DNA-based methods that estimate cell numbers from total DNA content — along with the limitations of each approach.

The story changes with the work of Suzana Herculano-Houzel and colleagues, who developed the isotropic fractionator, a clever “brain-cell counting recipe” that breaks tissue into a suspension of labeled nuclei. Using fluorescent markers to distinguish neuronal cells, this method provided a more precise estimate of about 86 billion neurons — and revealed that the number of glial cells is similar to neurons, not 10:1 as once believed.

Join me to see how scientists actually count the cells that make us who we are, why earlier estimates were off, and what modern neuroscience tells us about the true cellular makeup of the brain.

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