Your aging dog might help crack one of medicine's hardest questions
Doges Editorial · 2026-05-10 · 5 min read
A University of Arizona researcher noticed something strange about dog brains: Great Danes and Chihuahuas age at roughly the same cognitive rate, despite wildly different lifespans. A new two-year study wants to understand why — and whether the answer has anything to do with Alzheimer's.
A Great Dane lives about 8 years on average. A Chihuahua lives closer to 15. By the standard logic of biology — larger animals burn through their cellular resources faster, age more rapidly, die sooner — you would expect a Great Dane's brain to show signs of decline far earlier. The cognitive assessments should reflect the shorter lifespan. They don't.
When Evan MacLean, associate professor of veterinary medicine at the University of Arizona, began reviewing data on cognitive aging across dog breeds, the pattern that came back was surprising. Brain aging, in dogs, appears to be decoupled from body size. A Great Dane's mind ages at roughly the same rate as a Chihuahua's, despite everything else being different.
The implication, MacLean noted, is strange and a little melancholy.
Based on their different lifespans, you might expect large dogs like Great Danes to develop signs of dementia around 8 years old, but small dogs like Chihuahuas to have a later onset — somewhere in their teens. But that's not what we find. The implication is kind of interesting: it means that big dogs may just die before they acquire any kind of cognitive dysfunction.
— Evan MacLean, associate professor of veterinary medicine, University of Arizona
What dogs can tell us about Alzheimer's
MacLean is now launching a new study designed to understand why some aging dogs retain their cognitive sharpness while others develop symptoms that look very much like dementia. The project is called SIGNAL — the Study of IGF-1, Neurocognitive Aging and Longevity — and it is explicitly designed to generate findings that matter for human medicine, not just veterinary care.
The study is supported by the American Kennel Club Canine Health Foundation and will include 75 medium-sized dogs from the Tucson community, tracked over two years through blood samples and a series of in-person cognitive assessments. The researchers are actively looking for dogs to enroll now — specifically animals aged 10 to 13 years who weigh between 33 and 55 pounds.
We're hoping that by answering these questions, we'll not only be able to make discoveries that can advance dog health, but that we'll also learn things that are very relevant to human cognitive health, and specifically which may help us develop effective treatments and interventions for conditions like Alzheimer's disease.
— Evan MacLean, University of Arizona
Why dogs, not mice
The case for studying companion dogs rather than laboratory mice is one MacLean makes carefully. Alzheimer's has been one of medicine's most stubborn failures: hundreds of promising drug candidates tested in mice have then collapsed in human trials. Part of the problem, MacLean argues, is the model.
Laboratory mice are typically genetic clones of each other, housed in controlled conditions, living out biological timescales that compress years of aging into weeks. The disease produced in a mouse lab may not be the same disease that develops in a human brain over decades, in a complex social and environmental context.
Animals play a huge role in all kinds of medical research, but that often happens with mice kept in artificial laboratory conditions. Their world is much different than our own, and these mice are often clones of one another so there is no genetic variance. Companion dogs on the other hand are much more genetically diverse, share our world in very meaningful ways and receive high-quality medical care throughout their aging.
— Evan MacLean, University of Arizona
What that means, in practice, is that a discovery made in a companion dog living in a family home, eating real food, going on walks, experiencing the ordinary stressors and joys of domestic life, is more likely to translate into a discovery that holds in humans. The Dog Aging Project, a nationwide research initiative that has informed much of MacLean's prior work, is built on exactly this premise.
The IGF-1 question
The specific biological question SIGNAL is designed to answer involves IGF-1 — insulin-like growth factor 1 — a hormone that, among other roles, drives the remarkable variation in dog body size. A Great Dane and a Chihuahua are the same species; the difference between them is driven largely by differences in IGF-1 signaling during development. What MacLean noticed is that this same hormone may also influence how the aging brain holds together.
Previous studies have shown that manipulating IGF-1 can influence aging rates in other organisms, and there is evidence linking it to cognitive health in both humans and other animals. The relationship isn't simple — higher IGF-1 is associated with some positive neurological outcomes but also with elevated cancer risk. What SIGNAL aims to determine is whether, within dogs of similar size, those with higher IGF-1 concentrations perform better on cognitive tasks as they age.
What the dogs will actually do
The 75 dogs enrolled in SIGNAL will participate in in-person cognitive assessments at the Arizona Canine Cognition Center over the course of two years, alongside periodic blood draws to track hormone concentrations. MacLean's team has developed a battery of tasks — measuring spatial memory, executive function, and social cognition — that are designed to be pet-friendly: accessible to older dogs, adjustable for sensory limitations, and not requiring the dog to do anything they'd find distressing.
The research team includes colleagues from Arizona State University, Colorado State University, and Tufts University. The dogs they're looking for are 10 to 13 years old, weighing between 33 and 55 pounds — the medium-sized sweet spot that holds body size constant so that IGF-1 variations can be studied without confounding breed-specific differences in lifespan. Interested owners can email dogs@arizona.edu or enroll online through the Arizona Canine Cognition Center.
The dog who lives in your house
There is something quietly remarkable about the arrangement this kind of research creates. A senior dog who spends a Tuesday morning in a Tucson research facility, working through a series of tasks that look like puzzles and games, then goes home to nap on the couch, is potentially contributing to what may one day become a treatment for a disease that robs millions of people of their final years. The dog gives up nothing but time.
MacLean conducts his research alongside his own aging dog, Sisu. He is precise about the limits of what SIGNAL will answer on its own — the study is designed to generate mechanistic understanding, not to produce a drug or a diagnostic tool by itself. But the question it's asking is one that owners of older dogs already live with: why some minds hold, and others start to slip, and whether anything can be done about the difference.
The dog who hesitates at a corner she used to round without thinking, who stands at the foot of the stairs working something out, who stares at a familiar room as if trying to remember why she came in — she might be fine. But she also might be the beginning of an answer.