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Jul 18, 2023

The Mighty T-Rex Brain with Dr. Suzana Herculano-Houzel (podcast)

Can the number of neurons a brain has — or had — tell us about the cognitive capabilities of different species?

By Templeton Staff

The idea that humans "use only 10% of their brain" is a widespread misconception. Dr. Suzana Herculano-Houzel, a comparative neuroanatomist at Vanderbilt University, has said that the notion that "the proportion of glial to neuronal cells in the brain increases with brain size, or with body size, to the point that glial cells represent about 90% of all cells in the human brain has recently become so common in the neuroscientific research literature, as well as in textbooks, that stating it no longer requires citing the original sources." Motivated to explore how many cells compose the brains of different animals, she began the Herculano-Houzel lab in 2005, with the publication of the cell-counting method she created, the isotropic fractionator, which Herculano-Houzel says "consists of... turning brains into soup!" Listen in as she discusses her thought-provoking work for this episode of Many Minds.

Many Minds podcast host, cognitive scientist, and writer Kensy Cooperrider introduces the episode:

"When dinosaurs terrify us it’s because of their giant jaws and their sheer size, not because they were especially clever or crafty. (Except for those velociraptors in Jurassic Park, of course — they were terrifyingly wily.) But, in any case, who really knows? It’s all just fantasy and guesswork, right? I mean, how could we ever know how clever the dinosaurs actually were?

My guest today is Dr. Suzana Herculano-Houzel, a comparative neuroanatomist at Vanderbilt University. She studies the diversity and composition of brains across the biological world. For more than a decade now, Suzana and her colleagues have made the case that one of the most revealing things about a brain is not how big it is or how big it is relative to the body, but simply how many neurons it has. This basic variable, she argues, can tell us a lot about the cognitive capabilities of different species. Which means that if we were able, in some way, to estimate the number of neurons in the brain of some extinct creature, we could start to make inferences about its mind and its behaviors. 

Here, Suzana and I discuss a recent study of hers in which she does exactly that. She was able to reconstruct the make-up of the brains of certain dinosaurs — such as the theropods, a group that included the venerable Tyrannosaurus Rex. But, before we get to the T-Rex, we first lay some important groundwork. We talk about how Suzana counts neurons, by making a kind of brain soup. We discuss how number of neurons proves to be a better predictor of complex cognition than does the much-discussed Encephalization Quotient (or EQ). We then describe how the brains of different groups of animals tend to obey predictable scaling laws. And with that groundwork laid, we dig into Suzana’s estimate that, in terms of number of neurons, a T-Rex’s brain was comparable to a baboon’s. Which would mean that it was significantly cleverer than we long thought, that it was probably quite behaviorally flexible and long-lived and may have even had culture. As you might imagine, this study caused quite a bit of a stir and so, finally, Suzana and I discuss some of the criticisms that have been leveled against it."

Play the full episode with the above player.

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Templeton World Charity Foundation's Diverse Intelligences is a multiyear, global effort to understand a world alive with brilliance in many forms. Its mission is to promote open-minded, forward-looking inquiry in animal, human, and machine intelligences. We collaborate with leading experts and emerging scholars from around the globe, developing high-caliber projects that advance our comprehension of the constellation of intelligences.

Many Minds is a project of the Diverse Intelligences Summer Institute (DISI), made possible through a grant from TWCF to the University of California, Los Angeles (UCLA). The Many Minds podcast is hosted and produced by Kensy Cooperrider, with help from assistant producer Cecilia Padilla. Creative support is provided by DISI Directors Erica Cartmill and Jacob Foster. Artwork featured as the podcast badge is by Ben Oldroyd.