Big Dogs or Small Dogs? In Memory Tests, Big Brains Come Out on Top

Don’t tell grandma, but little dogs just don’t measure up to their larger counterparts. In a recent study comparing dog size and intelligence, scientists determined that bigger pups have better short-term memory and self-control than smaller pups, no matter how clever you think your Yorkie is. The findings could explain why big dogs like Labrador retrievers can always snoop out secret scraps.

The large brains of these large dogs are key to these findings, but brain size isn’t the whole story here. In fact, studying the extent of the link between brain size and intelligence in dogs was one of the goals of the Animal Cognition study, said study co-author and University of Arizona Ph.D. student Daniel Horschler.

The study reveals a link between dog brain size and a specific type of intelligence called “executive functioning,” which is often linked to self-regulation. It also allows individuals to plan, focus attention, remember instructions, and handle multiple tasks at once. Fortunately for small dogs, it isn’t the only type of intelligence that exists among dogs.

Dogs come in a wide range of brain sizes — the noggin of a Great Dane, for example, is quite unlike that of a pug. Accordingly, Horschler and his team examined data drawn from more than 7,000 purebred domestic dogs representing 74 different breeds. They estimated brain size on the basis of breed standards, but the actual data on dogs’ intelligence came from a citizen science website called Dognition.com, which collects cognition data on dogs from their owners.

Dog owners participating in the project tested the short-term memory of their pets by hiding a treat, in view of the dog, under plastic cups. By placing the treat in front of a dog and forbidding the dog to take it while the owner covered their eyes or walked away, they measured their pets’ self-control. When they compared brain size with intelligence using these data, the research team excluded the data taken from dogs who have already been trained to look for and not take treats.

In the end, they found that large dogs waited longer to munch on the forbidden cookie and were better than small dogs at remembering where treats were hidden.

Those two skills, say the scientists, are linked to executive functioning, which in turn is linked to the dogs’ big brains. Previously, said Horschler, studies on the link between big brains and executive functioning focused mostly on primates. This is one of the first times this link was shown to be shared across animal species, showing that it is not, as Horschler says, an “artifact of unique aspects of primate brain evolution.”

The good news for little pups is that the big dogs didn’t outdo the small dogs on any other measures of intelligence.

“The jury is out on why, necessarily, brain size might related to cognition,” Horschler explains. “We think of it as probably a proxy for something else going on, whether it’s the number of neurons that matters or differences in connectivity between neurons. Nobody’s really sure yet, but we’re interested in figuring out what those deeper things are.”

That reasoning is in line with an overall, growing understanding that a big brain doesn’t mean greater intelligence in every respect. Human brains are larger than chimpanzee brains and smaller than sperm whale brains, but we are considered more intelligent than both (although, perhaps not by much). Scientists hypothesize that the structure of the brain and the thickness of the cerebral cortex are more important than size.

In the future, Horschler wants to examine this relationship between size and cognition. He’d like to do comparative studies next, perhaps comparing a large standard poodle to a miniature one. Brains, in the end, might reveal who gets to run with the big dogs — and who stays on the porch.

Abstract: Large-scale phylogenetic studies of animal cognition have revealed robust links between absolute brain volume and species differences in executive function. However, past comparative samples have been composed largely of primates, which are characterized by evolutionarily derived neural scaling rules. Therefore, it is currently unknown whether positive associations between brain volume and executive function reflect a broad-scale evolutionary phenomenon, or alternatively, a unique consequence of primate brain evolution. Domestic dogs provide a powerful opportunity for investigating this question due to their close genetic relatedness, but vast intraspecific variation. Using citizen science data on more than 7000 purebred dogs from 74 breeds, and controlling for genetic relatedness between breeds, we identify strong relationships between estimated absolute brain weight and breed differences in cognition. Specifically, larger-brained breeds performed significantly better on measures of short-term memory and self-control. However, the relationships between estimated brain weight and other cognitive measures varied widely, supporting domain-specific accounts of cognitive evolution. Our results suggest that evolutionary increases in brain size are positively associated with taxonomic differences in executive function, even in the absence of primate-like neuroanatomy. These findings also suggest that variation between dog breeds may present a powerful model for investigating correlated changes in neuroanatomy and cognition among closely related taxa.