The Knowledge is a memorised map of London, that all black cab drivers in central London has to have, which includes thousands of landmarks, some 25,000 streets and also all the theatres and the order of them on Shaftesbury Avenue.

The Knowledge of London Examination System, which often takes 12 attempts to pass, is a brutal learning process that can take between 3 to 4 years to complete. Even after the learning process, only half the trainee cabbies ace the exam.

Successfully learning The Knowledge, creates a greater volume of nerve cells in the brain’s hippocampus, according to a report published in the journal Current Biology.

Eleanor Maguire and Katherine Woollett from the neuroimaging center at University College London, conducted a lengthy study which involved following 31 controls who weren’t training to become taxi drivers and 79 trainee cab drivers. Over time, the pair studied their performance on memory tasks and took snapshots of their brain structure using MRI.

The participants of the research displayed no apparent differences in memory or brain structure at the beginning of the study. The anterior hippocampus and the posterior hippocampus, which had been shown in previous research, to be larger in London cab drivers, was currently the same across all participants.

Only 39 of the trainee participants passed the test, acquired commercial taxi insurance and became registered taxi drivers in the intervening years.

This gave the researchers an opportunity to further group the participants in segments; participants that passed, did not pass, and the controls who never trained.

Now with The Knowledge exam over, the researchers discovered an increase in grey matter, the nerve cells in the brain where processing takes place – in the back part of the hippocampus of the trainees who passed the test. Those who didn’t learn or even failed the exam, had no changes to their brain structure.

In memory tasks that involved recalling landmarks around London, both the successful and failed cabbies were better than the control group. On the other hand, other tests that were not related to London, such as recalling complex visual information, who failed The Knowledge, were better than the registered cabbies.

Maguire said, “By following the trainee taxi drivers over time as they acquired — or failed to acquire — ‘the Knowledge’, we have seen directly and within individuals how the structure of the hippocampus can change with external stimulation,

“The human brain remains ‘plastic‘even in adult life, allowing it to adapt when we learn new tasks.”

What isn’t so clear, is whether those people who passed the exam had some inherent advantage over those who failed.

Maguire said, “Could it be that those who qualified are genetically predisposed towards having a more adaptable, ‘plastic’ hippocampus?

“This leaves the perennial question of ‘nature versus nurture’ still open.”