The world's largest dementia research experiment, which takes the form of a video game, has indicated the ability to navigate declines throughout life.
The findings, presented at the Neuroscience 2016 conference, harnessed data from 2.4 million people who downloaded the game.
Getting lost is one of the first symptoms of Alzheimer's disease.
And the researchers at University College London believe the results could help make a dementia test.
Sea Hero Quest is a nautical adventure to save an old sailor's lost memories.
With the touch of a smartphone screen, players sail a boat round desert islands and icy oceans.
The game anonymously records the player's sense of direction and navigational ability as they work their way through the levels.
Some require them to weave through waterways and fire a flare back home, while others challenge them to memorise a sequence of buoys and then sail round them.
Data harnessed from the flare levels is the first to have been analysed, by scientists at University College London.
And it suggests the sense of direction declines consistently after the teenage years.
Players aged 19 were 74% accurate at firing the flare back home, but accuracy fell year by year until it reached 46% at age 75.
Dr Hugo Spiers told the BBC: "What we're able to announce to the world is it does decline across the lifespan, the ability to shoot the flare back to the target - that sense of direction."
The data also suggests men have a slight better sense of direction than women and that the Nordic nations outperform the rest in the world, although it is not yet clear why.
- people in better health, common in Nordic countries, retain their navigational abilities longer
- coastal nations create better navigators
- a genetic "Viking blood" boost to navigational skills
The point of the research is to develop a way of diagnosing dementia in its earliest stages - something not yet possible.
Becoming completely disorientated is normally rare, but is more common in people with Alzheimer's disease.
Having a record of the normal decline in the internal compass could help doctors spot patients developing Alzheimer's.
Dr Spiers added: "The value of a future test built from Sea Hero Quest is that we will be able to provide a diagnostic for Alzheimer's dementia and a tool that allows us to monitor performance in drug trials."
Hilary Evans, the chief executive of Alzheimer's Research UK, said: "Sadly, we hear all too frequently of people getting lost and being found miles away from home.
"Researchers believe that these problems with spatial navigation could form the basis of a diagnostic test for the early stages of diseases like Alzheimer's, which could add a valuable tool to a clinician's diagnostic armoury.
"For any new diagnostic tool to be effective, it must take into account natural variation in a particular skill or ability across the population."
Using the game has provided scientists with unprecedented amounts of data from across the globe.
The data collection from 2.4 million people passing some time in the evening or on the way to work would have taken 9,400 years in the lab.
This project was funded by Deutsche Telekom and the game was designed by Glitchers.
Michael Hornberger, a professor of applied dementia research at the University of East Anglia, said: "The amount of data that has already been generated by people playing Sea Hero Quest all around the world is phenomenal and is enabling us to reveal a vital global benchmark of how people, of all ages and from all over the use spatial navigation."
Australian woman gets pregnant twice in 10 days
An Australian woman who was told she might never become pregnant says she has given birth to twins conceived 10 days apart.
Kate Hill was receiving hormone treatment for polycystic ovary syndrome, a condition that meant she was not ovulating.
She apparently conceived twins at different times despite only having unprotected sex once during that time.
It is very rare for a woman to conceive a second time when already pregnant.
Most twins are the result of a woman releasing two eggs at the same time, or, less commonly, a fertilised egg subsequently splitting into two.
The twin girls, Charlotte and Olivia, were born 10 months ago with different sizes, weights and gestational development, according to reports.
"We actually did not realise how special that was until they were born," Mrs Hill told Australia's Seven Network.
Pregnancy normally stops the monthly cycle of ovulation but very rarely a woman can release another egg after conceiving. If this is fertilised it could also implant and develop into a healthy pregnancy.
It is believed only 10 cases of the phenomenon, known as superfoetation, have been documented across the world.
Speaking about the rare conception, Mrs Hill's husband Peter joked: "Hole in one, maybe."
The couple's obstetrician Brad Armstrong said the condition was so rare he was forced to search for it online.
"I could not find any literature in the medical review websites at all," he said.
NHS send-to-all email causes turmoil
An email that was accidentally sent to all the NHS's staff in England has caused havoc.
One of the health system's employees fired off the message on Monday morning without realising they had copied in 840,000 of their colleagues.
The action quickly clogged up the system and was exacerbated by users hitting "reply all" to complain.
The distribution list was disabled at 10:00 GMT, but some users continue to have problems.
The secure email system is used by NHS staff and other approved organisations to discuss healthcare and related activities.
"It's driving me bananas," one doctor - who asked not to be identified - told the BBC.
"The thing is hundreds of people have been replying to all.
"My NHS email is very important to me because it's the only secure way I can send and receive anything safely about my patients.
"So, this is a major problem [and] potentially a risk to patients."
A spokeswoman for NHS Digital said it was not a member of its IT team who had sent the message, but declined to identify the culprit, saying they were not to blame.
"A number of email accounts have been operating slowly," said NHS Digital in a statement.
"This was due to an NHS Mail user setting up an email distribution list which, because of a bug in the supplier's system, inadvertently included everyone on the NHS Mail list.
"As soon as we became aware of the issue, we deleted the distribution list, so that no-one else could respond to it.
"We anticipate the issue will be rectified very soon."
What do you think? Have you played this game yet? Would you be wqorried about the younger baby's health? What do you make of this blunder?
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