Raccoons Are Rather Smart With Less Than 3% As Many Neurons as Humans

 A recent article in the Independent is entitled "I studied the brains of raccoons. Here’s what it tells us about human intelligence." We have an article written by a neuroscientist (Kelly Lambert) who correctly describes how smart raccoons are; but her article may lead to wrong ideas about the brains of raccoons. 

Speaking of raccoons, the neuroscientist states, "the species – Procyon lotor – is known for its impressive intelligence, curiosity and problem-solving skills." We have part of the article suggesting that raccoons were so clever that they were not used as research subjects, because the raccoons kept figuring out ways to escape through ventilation ducts in research laboratories.  We read this:

"And the role confusion continues today with glimpses of humanlike behaviors in raccoons as they enter our living spaces. One report described raccoons interacting with playground equipment at a child care center on Canada’s west coast in ways similar to human children, and even breaking into classrooms as if they were auditing the morning lesson....After introducing young raccoons to slinkies, puzzles and blocks, I sat in awe as they interacted with these objects with the focused enthusiasm of preschoolers on a mission....Early behavioral research suggested that raccoons can learn a task, walk away and later return to solve it accurately – as if having mentally rehearsed the solution. In contrast, other species, including dogs and rats, needed to maintain continuous focus. Scientists have speculated that raccoons have mental imagery capabilities similar to humans."

But none of this should be possible, according to "brains make minds" claims -- because raccoons have fewer than 3% of the cerebral cortex neurons that humans have. Humans are believed to have about 86 billion neurons, with about 20 billion of them in the cerebral cortex. But according to a paper co-authored by Lambert, "The raccoon cerebral cortex has an average 438 million neurons." 

Does Lambert tell us in her Independent article that raccoons have less than 3% of the cerebral cortex neurons of humans? She does not. Instead she gives us the following paragraph that seems designed to give us the wrong idea about raccoon brains: 

"Working with neuroscientist Suzana Herculano-Houzel, my laboratory at the University of Richmond has found that raccoons pack an astonishing number of neurons – an amount comparable to primates – into their brains. Scaled up to size, a raccoon brain would contain roughly the same number of neurons as a human brain."

The statement seems designed to give the casual reader the idea that raccoons have neurons numbers similar to humans. They do not. Raccoons have less than 3% of the cerebral cortex neurons of humans. And comparing total neurons in raccoons and humans, we find that the total number of neurons in raccoons (about 2 billion) is less than 3% of the total number of neurons in humans.  The page here gives the total numbers. 

Trying to explain why raccoons with so few neurons can be so smart, Lambert states this: 

"In collaboration with ecologist Sara Benson-Abram’s research team, we also found that raccoons with more sophisticated cognitive abilities had more neural cells in the hippocampus, reinforcing the idea that their learning and memory capacities map onto similar brain systems as those in people. Taxi drivers in London, who frequently use their knowledge of the 25,000 streets in London, also have a larger hippocampal area."

We have no paper reference for these claims, which are not well-founded. The first claim by Lambert is probably referring to the paper here, co-authored by her, Sara Benson-Abram and others. Its study group sizes were way too small for the study to qualify as any decent evidence for the claim that "that raccoons with more sophisticated cognitive abilities had more neural cells in the hippocampus." The study group size corresponding to "raccoons with more sophisticated cognitive abilities" was a study group of only 7 animals. No claim about a greater number of hippocampal neurons should be taken seriously unless that study group was 2 or 3 times larger, consisting of at least 15 or 20 animals. 

There is also no robust evidence that "taxi drivers in London, who frequently use their knowledge of the 25,000 streets in London, also have a larger hippocampal area." Such claims are based on the study  “Navigation-related structural change in the hippocampi of taxi drivers” which found no notable difference outside of the hippocampus, a tiny region of the brain. Even in that area, the study says “the analysis revealed no difference in the overall volume of the hippocampi between taxi drivers and controls.” The study's unremarkable results are shown in the graph below. 

The anterior part of the left half of the hippocampus was about 25% smaller for taxi drivers (100 versus 80), but the posterior part of the right half of the hippocampus was slightly larger (about 77 versus 67). Overall, the hippocampus of the taxi drivers was about the same as for the controls who were not taxi drivers, as we can see from the graph above, in which the dark bars have about the same area as the lighter bars. 

By claiming that "taxi drivers in London, who frequently use their knowledge of the 25,000 streets in London, also have a larger hippocampal area," Lambert is repeating one of the groundless "old wives' tales" of neuroscience, which is something that neuroscientists frequently do. 

Raccoons are not the only species that acts in a very smart way, despite having less than 3% of the neurons of humans.  Ravens show a wealth of high-level cognitive abilities, even though they have only about as many neurons as raccoons -- about 2 billion, which is less than 3% of the number of neurons that humans have.