London cabbies who drive the city’s iconic black taxis have been required since 1865 to pass a difficult test known as “the Knowledge” to prove that they can find 100,000 businesses and landmarks in a labyrinth of tens of thousands of streets.

The series of exams — which take three to four years to complete — have been hailed as possibly the most difficult memorization test in the world. To be fully licensed with a “green badge” to drive anywhere in London, a cabbie needs to know how to plot routes without a GPS on about 26,000 streets spanning a six-mile radius from London’s center point, Charing Cross.

But London cabbies’ skills are now being tested for a different reason: to determine whether their brains hold clues that might be applied to Alzheimer’s disease research.

A project called Taxi Brains is underway at University College London to study the brains of London cabbies as they map out taxi routes while undergoing MRI scans.

“London cabbies have remarkable brains,” said Hugo Spiers, a professor of cognitive neuroscience who set up the project with three doctoral students. He cites a 2000 study done by Irish neuroscientist Eleanor Maguire showing that learning the Knowledge causes positive changes in a taxi driver’s brain.

The hippocampus regions of taxi drivers’ brains — which play an important role in learning and memory — appear to grow larger the longer the drivers are on the job, he said, while the same region is known to shrink in people with Alzheimer’s disease.

“We don’t know much about how taxi drivers use their hippocampus during route planning,” said Spiers. “And how do they use other brain regions to solve the task of navigating 26,000 streets? Can we explain why they might be quick to plan out one route and take a while to think out another one? It’s something we need to know more about.”

The answers could lead to the development of diagnostics to detect dementia earlier and treat patients sooner, he said, noting that he and his team plan to forward their study results to Alzheimer’s Research UK and have preliminary findings available sometime next summer.

Taxi drivers who signed up for the MRIs from July through October said they were happy to discover there was another way to use the memorization skills they’d acquired through the Knowledge. There are 30 cabbies in the study.

For Matt Newton, 44, there was also a more personal reason to participate. Newton’s father died of dementia in 2019, he said, so he felt a strong sense of duty to be part of it.

“I know what a devastating disease it is for the person [who has it] and the family,” he said. “It was only a few hours of my time, so I was happy to help.”

Newton, a cabbie since 2016, said he signed up for the Taxi Brains project when he spotted an ad over the summer calling for green badge taxi driver volunteers.

Inside an MRI scanner, Newton was shown photos of London landmarks and street names and asked to map out 120 routes in his mind from Point A to Point B while his brain was scanned, he said.

He and the other cabbies were also asked to play Sea Hero Quest — a video game often used in scientific research to test a brain’s complex spatial navigation abilities. For their time, they each received about $40 and an MRI photo of their brain, said PhD researcher Chris Gahnstrom.

“They were by far the nicest and most forthcoming group I’ve had the pleasure to run experiments with,” he said.

“London cabbies are ideal participants [for this study] because there is no other professional group quite like them, especially in the field of spatial navigation,” added Gahnstrom, 31. “They’re a large group of expert navigators who have all had to learn an immense amount of similar information that they are required to use on a daily basis.”

“This is what sets them apart,” he said, noting that the Taxi Brains team hopes to identify which subregions of the hippocampus are most significantly affected in the brains of those who have studied the Knowledge.

Newton said he wasn’t surprised to learn that London cabbies’ brains develop more volume the longer they’re on the job.

“I actually enjoyed studying the Knowledge, but it was extremely difficult — most people give up,” he said.

“I studied 12 hours a day, seven days a week for three and a half years,” added Newton, who worked as a network analyst for 20 years before he decided to switch careers and climb behind the wheel. Cabbies who complete the Knowledge earn in the range of $50,000 to $100,000 a year, depending on how many hours they drive.

“I started out learning the ‘Blue Book’ — a set of 320 runs between various points in London,” he said. “I started calling up 80 of these runs every day in my head, then driving the runs on a scooter. I learned hospital runs, theater runs, football runs, and ‘no traffic light’ runs before I applied to be a taxi driver.”

After he passed a written test, Newton then began the process of becoming a “black cabbie,” he said. At the beginning of his Knowledge quest, he was called into an examiner’s office every 56 days and asked to recite what streets he would take between two points in London for four different routes.

Once he’d scored enough points to move to the next level, Newton was called in every 28 days, and finally, every 21 days, he said.

“At each point, if you fail, you go back to the previous level,” he said. “You could study for three years and still end up back at the beginning. There is no guarantee that you’ll pass.”

Driver Rob Lordon became so fascinated by his own experience with the Knowledge that he decided to start a blog about it. And in 2018 he published a book, “The Knowledge: Train Your Brain Like a Cabbie.”

When he heard about the Taxi Brains project, he said he immediately felt compelled to sign up.

“I’m very fortunate that nobody in my family suffers from Alzheimer’s,” said Lordon, 40. “However, I’m fully aware of just how awful a disease it is, and if I’m able to help in just a small way, I thought it was important to do so.”

The test for the cabbie study was a cakewalk, he said, compared to negotiating London’s narrow, winding streets at rush hour.

“Driving in London has become increasingly stressful in recent years due to issues such as multiple road closures and ever-worsening traffic,” said Lordon. “So it was a pleasure to participate in the Alzheimer’s test. And good fun, too.”

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