By the time a cat reaches its late teens, it may start to behave differently — wandering the house at night, calling out more often, getting lost in familiar rooms. To many owners, these are signs of concerning ageing. To scientists, they are clues to a disease that could help solve one of medicine’s greatest mysteries.

A new study from the University of Edinburgh has found that cats with dementia develop brain changes strikingly similar to those in humans with Alzheimer’s disease. The work suggests that elderly cats could serve as a powerful natural model for the human condition, potentially accelerating the search for treatments.

“Dementia is a devastating disease — whether it affects humans, cats, or dogs,” said Dr. Robert McGeachan, the study’s lead author. “Our findings highlight the striking similarities between feline dementia and Alzheimer’s disease in people.”

When Dementia Comes to the Doorstep

For many cat owners, the signs of cognitive decline can be subtle — until they are impossible to ignore. Kägi, a cat owner in Switzerland, recently shared on Reddit the story of Maolo, an elderly cat from down the street. Maolo and his family had moved away from the home he once knew, but he continued to show up at Kägi’s door, as if it were still his own.

“This, with the strong suspicion that he has dementia, because he also often forgets that he has just eaten and then still asks for another meal, seems to be the most plausible explanation,” Kägi said.

Kägi’s own cats, Mocca and Cosmo, are much younger, but still demand a “dessert” after dinner. Maolo’s visits, however, feel different — more disoriented.

Such behaviour is more common than many realise. A PetMD article by Dr. Melissa Boldan notes that more than a quarter of cats aged 11 to 14 show at least one sign of dementia. That number jumps to about half in cats over 15. The symptoms include wandering aimlessly, using the wrong door to go outside, struggling to find their way out of rooms, becoming stressed in familiar places, and soiling inappropriately.

Other clues are more subtle: asking for food at odd times, sleeping in unusual patterns, waiting at the window for people who aren’t due home, or seeming indifferent to affection from those they once loved.

A short video of Maolo lingering outside Kägi’s door, posted to social media, quickly went viral — drawing thousands of sympathetic comments. “Awww poor thing. Might want to just lead him back home then,” one user wrote. Another urged, “Let him in and give food, pets, and snacks… seriously.”

A Toxic Hallmark Shared Across Species

The Edinburgh team examined the brains of 25 cats after death. Some had shown clear signs of feline cognitive dysfunction syndrome (CDS) in life. Symptoms include confusion, sleep disruption, changes in social behaviour, and loss of house-training. Others were old but cognitively normal, and a smaller group were young adults.

Under the microscope, the researchers found a familiar villain: amyloid-beta. This toxic protein, one of Alzheimer’s defining features, was lodged not just between brain cells but inside synapses, the microscopic junctions where nerve cells communicate. In humans, amyloid-beta is thought to disrupt those connections, eroding memory and cognition.

In both aged and CDS-affected cats, amyloid-beta was more abundant than in young cats. The protein’s presence inside synapses matched patterns seen in human Alzheimer’s brains and in laboratory mouse models.

The Brain’s Cleanup Crew Turns Destructive

The study went further, revealing that amyloid-beta may be triggering the brain’s own immune cells (microglia and astrocytes) to engulf synapses. In healthy brains, this pruning process shapes neural circuits during development. In disease, it can accelerate cognitive decline.

Using high-resolution confocal microscopy, the team showed that in regions rich in amyloid-beta plaques, microglia and astrocytes contained pieces of synapses. In cats with dementia, the amount of engulfed, amyloid-laden synapses correlated with the overall amyloid burden — a relationship not seen in cognitively healthy aged cats.

“Because cats naturally develop these brain changes, they may also offer a more accurate model of the disease than traditional laboratory animals, ultimately benefiting both species and their caregivers,” Dr. McGeachan said.

Why Cats Could Change Alzheimer’s Research

For decades, scientists have relied heavily on genetically engineered rodents to study Alzheimer’s. These models are useful, but they don’t naturally develop dementia. Cats do — and they share many of the same brain pathologies as humans, including amyloid plaques, tau tangles, and brain atrophy.

Professor Danièlle Gunn-Moore, an expert in feline medicine and a co-author of the study, believes this could transform care for both species.

“Feline dementia is so distressing for the cat and for its person,” she said. “It is by undertaking studies like this that we will understand how best to treat them. This will be wonderful for the cats, their owners, people with Alzheimer’s and their loved ones.”

The findings also open the door to testing whether new Alzheimer’s treatments — such as monoclonal antibodies targeting amyloid-beta — might help ageing pets. If successful, the research could bridge veterinary and human medicine in unprecedented ways.

The findings appeared in the European Journal of Neuroscience.