“They’re quite good,” he said admiringly.

But the story unfolding on their screens – about a young man helping his elderly father track down lost memories of their time together on board the family boat – gives him a pang. It makes him think of his grandmother, who died after being diagnosed with dementia years ago. And it makes him think of his patients with Alzheimer’s disease, who complain of finding themselves lost in familiar places. They have trouble finding the grocery store they’ve been to 100 times. Hornberger wonders how they would navigate this fictional world.

One day, he hopes, he’ll get to find out.

Hornberger, a dementia researcher at the University of East Anglia, is the brain behind an unlikely effort to turn a video game into a tool for research. His game, “Sea Hero Quest,” is aimed at helping to spot early signs of dementia, and it debuted to great fanfare this week. It’s already been downloaded some 150,000 times, according to Alzheimer’s Research UK, a non-profit that supported the project. If each person who downloaded plays for just two minutes, they’ll supposedly provide researchers with the equivalent of 70 years of lab data on human spatial memory and navigation.

All that data will help researchers establish a baseline understanding of how a healthy mind works – or how it makes its way through the icy rivers and bustling oceans of “Sea Hero Quest,” at any rate. From there, they can conduct clinical trials to see how the paths taken by patients with dementia differ. And after that?

“This game can be a diagnostic tool that will be available in every language in every country,” one of Hornberger’s collaborators, Hugo Spiers, proudly said.

Spiers is a neuroscientist at University College London and an expert in spatial perception – one of the earliest skills to deteriorate in a patient with early Alzheimer’s. When Hornberger first came up with the idea for a diagnostic video game, he knew he needed to contact his friend Hugo first.

“It was one of the strangest phone calls of my life,” said Spiers. “He said, ‘We’re thinking of running this giant project looking at navigation all across the world and using it to test for dementia, would you like to take part?’ And I just did a double take.”

Spiers, accustomed to the slow, incremental work typical of most scientific research – studies that spend years analyzing a few hundred or even a few dozen subjects’ test results – didn’t know if something so big and complex was even possible. “I’m a skeptical scientist,” he said, congenitally wary of hyped up theories and overblown claims.

But Spiers knew Hornberger, and he knew that a better diagnostic tool for Alzheimer’s was needed. For now, the disease often isn’t caught until patients begin showing signs of memory loss. At that point, it’s often too late to do much to slow the progress of the disease, let alone halt it. The tests that do exist are largely language-based and difficult to translate, so there’s no one tool that works worldwide. (A note on terminology: dementia is a general term for hazardous decline in mental ability. Alzheimer’s disease can cause dementia, as can brain tumors and other illnesses.)

But a game that examined navigation could be “absolutely monumental,” Spiers said. It was language-free. And, strange though it initially seemed, a video game was actually a natural fit for this kind of research – clinicians already use virtual reality to study how people perceive themselves in space.

By the end of the phone call, Spiers had jumped on board.

For the past year, with funding from the communications giant Deutsche Telekom, he, Hornberger and six other scientists worked with designers from the app company Glitchers to create a game that would serve science without seeming to.

There are two major types of challenge in the current version of Sea Hero Quest (a third will be added in an update to the game scheduled for later this year), all based on real tools already used by brain researchers. Spier calls them “experiments embedded within the game.” One challenge has players memorize maps, then use them to make their way to checkpoints. This tests memory and visual perception. The second asks players to sail to a spot and then “fire a flare” back to their starting point. In the narrative of the game, this is to let their friends on shore know where they are. But for the researchers behind the scenes, it tests players’ ability to situate themselves in space.

Both these skills rely on the hippocampus, a seahorse-shaped structure nestled in the middle of the brain. Hornberger remarked that this body part is measurably larger in London taxi drivers, who spend their whole careers learning how to know exactly where they are at all times. But the hippocampus is one of the first parts of the brain to deteriorate in patients with Alzheimer’s. That’s why so many find themselves misplacing things, or suddenly feeling disoriented in the middle of their own homes, long before they realize that something more insidious is going on inside their heads.

Every 500 milliseconds, information about players’ heading and position is anonymously sent back to Sea Hero Quest’s creators. They can then analyze that data to find the paths most and least often taken by navigators and to figure out where those who get lost go wrong. That will give them a basic understanding of how healthy brains respond to the tasks in the game, findings they plan to report on by the end of the year.

Eventually, Hornberger and his colleagues hope to conduct clinical trials based on the game, the first step toward getting it approved as a diagnostic tool.

That possibility is still a long way off, Spiers cautioned, and it’s by no means a silver bullet. Having a universal diagnostic test won’t stop people from getting Alzheimer’s or cure those who already have it. What it could do is help doctors catch the disease earlier, making it more likely that it can be treated. It might also help test the effectiveness of new treatments by giving an objective measure of whether a patient’s spatial perception is improving.

In the meantime, Hornberger will keep encouraging others to download the game. He’ll even give it a few tries himself.

“Oh, I’ve played it a hundred times,” he said, laughing. “It’s fun.”

(c) 2016, The Washington Post · Sarah Kaplan