Exercising your brain is the best way to avoid accidents. Just ask London's black cab drivers

Olivier Oullier examines the world's toughest memory test to explain the brain's functioning

A photo illustration shows the Uber app and a black cab in London, Britain June 26, 2018. REUTERS/Simon Dawson/Illustration
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As someone who travels far too much, I really enjoy any hack or app that eases my trips. The convenience of being able to order and pay for a car with my phone when I land in a new place is definitely something I enjoy a lot. But recently I had a couple of not so great experiences with Uber drivers who asked me for my phone to use Waze or Google maps because their own data plan had expired.

Without a navigation system, they were unable to deliver the service I was paying for.

This is the kind of unfortunate experience that is unlikely to happen if you go to London and take a black cab. To get you to your destination, London taxi drivers rely on their brains, not on apps or GPS. One of the reasons they do not need digital help to find their way is the training they undergo and the test they have to pass to get their taxi licence. Known as "The Knowledge", it is by far the hardest test in the world for taxi drivers. The amount of information one is expected to remember is simply astonishing.

To prepare for the test, drivers need to have fully memorised 25,000 London streets and roads located within a six-mile radius of Trafalgar Square. Add on top of this 20,000 points such as monuments, hospitals, police stations, theatres, shops and schools, and then you start understanding why The Knowledge’s success rate is as low as the test to join the United States Navy SEALs.

It takes between two to four years for drivers to complete The Knowledge, following several oral appearances. Preparing for those appearances is a full-time occupation, requiring candidates to drive around London on scooters and to study maps day and night. During the last oral interviews, in addition to the locations of theatres, drivers are also expected to know what shows are playing there.

Personally, it amazes me that people can memorise all of this and pass the test. But some do. So what makes the brains of London taxi drivers so special?

Several neuroscientists have tried to answer this question over the past 20 years thanks to structural and functional magnetic resonance imaging – big brain scanners one can find in hospitals that allow us not only to measure the volume but also to track changes of activity in brain areas.

In 1997, a group of London-based researchers led by Eleanor Maguire observed increased activity in the right hippocampus of licensed London taxi drivers as they were recalling a complex route. Dr Maguire and her colleagues concluded that this region of the brain known to contribute to memory processes “is involved in the processing of spatial layouts established over long time courses”.


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In subsequent studies, researchers found that the brains of London taxi drivers were physically different compared to other people. The volume of their posterior hippocampus was not only bigger than what was measured in non-taxi drivers but correlated positively with the number of years of they drove a taxi.

Similar differences were also found when comparing the brains of taxi and bus drivers. The latter, following a fixed route every day, were not relying on their visual memory in the way taxi drivers did, and the volume of some parts of their hippocampus was not as big as their peers driving taxis.

Where it gets even more interesting is when other researchers from the UK, Switzerland, Germany and Bahrain found that when a driver follows a satellite navigation system, the demand on the hippocampus is lower than navigating without digital assistance. And the researchers suggested that relying on navigation assistance such as Waze could lead to a decrease in the volume of the hippocampus.

So is the use of GPS while we drive going to make our brains shrink, as some concluded after the discoveries of the last study? Not really.

But memory needs to be exercised on a daily basis and everything we do to keep it active is good. It is interesting to realise that we now have a tendency to rely less on our neural memory and more on the memory of our smart devices and computers. Telephone numbers are stored in our phones and we use navigation apps even during our daily commutes, sometimes to be informed about traffic, but some other time because we are just lazy.

As I discussed a few weeks ago in this column, there is a global increase in the number of car accidents due to the use of smart phones and other digital devices while driving. Distracted driving has become a major road safety risk not only because of texting and driving, but also because of the increasing number of distractions provided by the dashboard of cars, such as GPS.

To my knowledge there is no comparative data available so far that would indicate that a taxi driver relying exclusively on his or her memory is less likely to end up in a road crash, as compared to drivers not keeping their eyes on the road all the time because they are checking their GPS.

But this is something worth keeping in mind the next time you need a ride.

Professor Olivier Oullier is the president of Emotiv, a neuroscientist and a DJ. He served as global head of strategy in health and healthcare and is a member of the executive committee of the World Economic Forum