It’s a brutal learning process that can take three to four years to complete, with a final test — the Knowledge of London Examination System — that often takes 12 attempts to pass. Even then, ultimately only half of the trainee cabbies ace the exam.
According to a report published in the journal Current Biology, successfully learning this mental atlas of London’s spaghetti streets causes structural changes in the brain, affects memory and creates a greater volume of nerve cells in the brain’s hippocampus.
In a lengthy study, Eleanor Maguire and Katherine Woollett from the neuroimaging center at University College London followed a group of 79 trainee taxi drivers and 31 controls (who weren’t in training to become cab drivers). Over time they took snapshots of their brain structure using MRI and studied their performance on memory tasks.
At the start of the study, the participants showed no discernible differences in brain structure or memory. The posterior hippocampus and the anterior hippocampus — which had been found, in previous studies, to be larger in London taxi drivers — was currently the same across all participants.
In the intervening years, only 39 of the trainee group passed the test and went on to qualify as registered taxi drivers. This gave the researchers an opportunity to further divide the volunteers into three groups: those that passed, those that trained but did not pass, and the controls who never trained.
Now, with the exam over, the researchers found 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 that failed, or never learned, had no changes to their brain structure.
In the memory tasks, both the successful and failed cabbies were better than the control group at recalling London landmarks. However, at other tasks not related to the capital, such as recalling complex visual information, the controls and the trainees who failed to qualify were better than the registered taxi drivers who had “the Knowledge”.
“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,” said Maguire in a press release. “The human brain remains ‘plastic‘ even in adult life, allowing it to adapt when we learn new tasks.”
What’s less clear is whether those who ultimately succeeded at the exam had some inherent advantage over those who failed. “Could it be that those who qualified are genetically predisposed towards having a more adaptable, ‘plastic’ hippocampus?” Maguire said in the release. “This leaves the perennial question of ‘nature versus nurture’ still open.”