Which animal is smarter? Dogs or cats. It's an eternal argument and one virtually impossible to answer due to the abstract nature of intelligence. Throwing some scientific evidence into the debate is a new study from an international team of scientists attempting to quantify an animal's smarts by calculating the number of neurons in their cerebral cortex. The results don't bode well for our feline friends.

The research relied on a novel method for accurately measuring the number of neurons in a brain, specifically the cerebral cortex, developed by Suzana Herculano-Houzel, Associate Professor of Psychology and Biological Sciences at Vanderbilt University who is one of the authors of the new study. The cerebral cortex is the largest layer of the brain and is associated with many complex behavioral characteristics.

"I believe the absolute number of neurons an animal has, especially in the cerebral cortex, determines the richness of their internal mental state and their ability to predict what is about to happen in their environment based on past experience," says Herculano-Houzel.

So what was the final count for dogs versus cats? Dogs won out overwhelmingly with approximately 530 million cortical neurons, while cats were only found to have approximately 250 million cortical neurons. For a relative comparison, a human brain holds around 16 billion cortical neurons.

It's quite a significant difference, but what makes the metric even more interesting is that, when applied to other animals, the study did not see a consistent brain size to cortical neuron ratio. So the bigger the brain didn't necessarily mean more cortical neurons.

The brain of a common golden retriever dog, for example, was found to have more cortical neurons than a brown bear, which has a brain three times larger. In fact a brown bear was found to have a similar number of neurons as a cat.

As a side note, one of the brainiest animals from a brain size to neuron density perspective was the raccoon, which has a brain the size of a cat, but a neuronal density similar to that of a dog.

"Raccoons are not your typical carnivoran," says Herculano-Houzel. "They have a fairly small brain but they have as many neurons as you would expect to find in a primate … and that's a lot of neurons."

Of course, this kind of arbitrary brain measurement isn't an objective metric for such a complicated trait like intelligence. Feline intelligence is in fact a quite understudied academic area, mainly because cats are incredibly difficult to study. One comparative psychologist even went so far as saying, "it's easier to work with fish than cats."

This new study certainly isn't the end of the debate, but as Herculano-Houzel suggests, "we now have some biology that people can factor into their discussions about who's smarter, cats or dogs."

And regardless of which animal is smarter, at least cat owners can console themselves with another recent study that claims they are smarter than dog owners.

The new study was published in the journal Frontiers in Neuroanatomy.

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