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A Whale of a Brain: Comparing Whale and Human Neuroanatomy
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ResearchBlogging.orgHere's a pretty cool recent article in Scientific American that talks about two relatively recent studies and their implications for whale and dolphin cognition.

The author starts out by noting that whales have bigger brains than humans. I've made the argument here before that the human neocortex expanded through evolution finding a scalable modules (the minicolumn) and largely increasing the number of those modules.

So if cognitive ability is linked to the size of the brain, does that mean that whales are smarter than people?

Well, the first paper, "Cetaceans Have Complex Brains for Complex Cognition" by Marino et al., discusses some of the comparative neuroanatomy between cetaceans (dolphins and whales) and other mammals. Cetaceans apparently arose about 55 million years ago (that'd be about 10 million years after the dinosaurs went bye-bye). And so they have some interesting differences from other mammals. For one, they have a lot more gyri (those are the convolutions in the cortical sheet that make it look wrinkly). This may or may not be significant. It could just be a by-product of trying to cram a larger cortical sheet into a skull that's unable to increase in size due to other constraints (like the size of the birth canal).

Also, our neocortex has 6 layers, with layer 4 acting as the primary input layer. Whales don't even have a layer 4, so there are significant differences in how it is organized. Also, our layer 1 has very few neurons, while theirs is much more cell-rich. Whales also have spindle neurons, which were previously thought only to exist in primates and humans.

So are whales smarter than humans?

The second paper the article talks about is "Total neocortical cell number in the mysticete brain" by Nina Eriksen and Bente Pakkenberg. They specifically looked at the brain of Minke whales (a type of baleen whale with an unusually thick neocortex). Their cellular estimate for the Minke whale neocortex was 12.8 billion neurons. That's a lot more than most other mammals, but considerably less than the average human, with about 20 billion neocortical neurons. However, the whales have a lot more glial cells, which were once thought only to act as scaffolding for neurons, but have recently been shown to carry out some forms of processing. In whales, the large number of glia are thought to be necessary for thermoregulation of their brains.

Also, the SA article mentions that baleen whales generally have less sophisticated brains because they filter plankton and krill as opposed to whales that hunt. So I'm not sure if the kind of analysis done by Eriksen and Pakkenberg has been done on hunting whales.

So are whales smarter than humans?

Who the hell knows? They certainly have large, sophisticated neocortices. However, we're still just scratching the surface of how the primate neocortex works, so carrying out a direct comparison with a species that diverged that long ago, and which has a different global organization...well, that's rough.

This type of work is pretty interesting though. It's far from providing solid answers, but it gives us more pieces to fit in the puzzle.

Eriksen, N., Pakkenberg, B. (2007). Total neocortical cell number in the mysticete brain. The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology, 290(1), 83-95. DOI: 10.1002/ar.20404

Marino, L., Connor, R.C., Fordyce, R.E., Herman, L.M., Hof, P.R., Lefebvre, L., Lusseau, D., McCowan, B., Nimchinsky, E.A., Pack, A.A., Rendell, L., Reidenberg, J.S., Reiss, D., Uhen, M.D., Van der Gucht, E., Whitehead, H. (2007). Cetaceans Have Complex Brains for Complex Cognition. PLoS Biology, 5(5), e139. DOI: 10.1371/journal.pbio.0050139

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