The process of learning to navigate and locate thousands of city streets and places of interest causes structural changes in the brains of London taxi drivers, according to a new study published in Current Biology on 8 December. The findings should encourage those interested in life-long learning and undergoing rehabilitation after brain injury, as they show the adult brain is more “plastic” than we thought when faced with new challenges, said the authors.

To become licensed to drive a cab in London, would-be taxi drivers have to acquire what is commonly termed “The Knowledge”, which entails learning and locating 25,000 streets and 20,000 landmarks, as well as their intricate layout. It usually takes three to four years to accomplish the feat, and only around half the trainees eventually pass the exams.

Katherine Woollett and Eleanor Maguire of the Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, conducted the research. Maguire’s earlier studies of London taxi drivers found they have more gray matter in the back part of the hippocampus than non-taxi drivers, and less in the front part.

The hippocampus, which sits deep inside the brain in the medial temporal lobe, plays a key role in consolidating short-term memory into long-term memory and also in spatial navigation. Maguire’s earlier studies suggested that the observed changes occurred in order to accomodate an “internal map” of London’s streets and landmarks.

In this latest study, Woollett and Maguire looked for evidence that might support or disprove this suggestion. They enrolled a group of trainee taxi drivers, and another group of drivers who were not taxi drivers (as the controls) and measured them now and again over time. They took two types of measurements: brain scans and tests of memory.

At the start of the study period, there was no discernible difference between the two groups in either measure: their brain structures were largely similar and so were the scores on memory tests.

However, by the end of the study period, some three to four years later, those trainees who passed the exams showed an increase in grey matter at the back of the hippocampus, while those who did not pass did not, and neither did the non-taxi driver controls.

The authors found that the structural brain changes in those who passed occurred in step with changes in their memory test results.

“In those who qualified, acquisition of an internal spatial representation of London was associated with a selective increase in gray matter (GM) volume in their posterior hippocampi and concomitant changes to their memory profile,” write the authors.

Maguire told the press:

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

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,” she added.

She and Woollett suggest their findings may reflect the generation and persistence of new neurons in response to significant cognitive challenge: the hippocampus is known to be one of the few areas of the brain where new neurons do form.

Successful training could also help to strengthen the connections between existing neurons, they add.

However, what is not so clear, is whether those who passed the exams already had some inherent advantage that was not apparent in the measures at the outset.

“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,” said Maguire.

Written by Catharine Paddock PhD