14 December 2011

Taxi driver training changes brain structure

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Learning the locations of London's 20,000 landmarks and the 25,000 streets and 320 routes that connect them has changed the growth of taxi drivers' brains.
plastic brain

As London taxi drivers in training are busy learning how to navigate the city's thousands of streets and places of interest over a period of years, the experience actually changes the very structure of their brains, say scientists. Credit: iStockPhoto

SYDNEY: Learning the locations of London’s 20,000 landmarks and the 25,000 streets and 320 routes that connect them has changed the growth of taxi drivers’ brains.

A new study, published in the current issue of Current Biology, shows that learning alters the structure of the hippocampus – the horse shoe-shaped brain region that is responsible for memory and spatial navigation. This finding challenges the long-held notion that the brain is inflexible over an adult’s lifetime.

“The human brain remains ‘plastic’ even in adult life, allowing it to adapt when we learn new tasks,” said Eleanor Maguire, a neuroscientist at University College London and co-author of the study. Maguire said this evidence that the brain is much more adaptable than once thought suggests that it could sustain life-long learning and successful rehabilitation following an injury.

Changing the plastic brain

In previous research, Maguire showed that London taxi drivers have more grey matter – clusters of neurons and other brain cells – in the posterior hippocampus of their brains compared to control subjects. She also reported that London taxi drivers have smaller anterior hippocampi as well as a poorer ability to learn new visual information than others. According to Maguire, this shows that memory improvement in one domain may come at the expense of memory performance elsewhere.

This new study is the first to suggest that the learning of new information actually causes the hippocampus’ volume to increase over a period of three to four years.

“It shows undoubtedly that normative changes in brain structure are a result of environmental changes and demands, and this knowledge is pivotal to understanding the characteristic ability of the brain to adapt,” said Arne May, a neuroscientist at the University of Hamburg in Germany, who did not contribute to this study.

Acquiring ‘the Knowledge’

For the experiment, Maguire followed 79 taxi drivers over their entire training period as they learned what is called ‘the Knowledge': thousands of London landmarks, including Big Ben and St. Pauls, and streets and the major routes connecting them. Trainees are tested throughout the three-to-four year process – required to recite the easiest route between two points and name landmarks they would see along the way. Only about half of trainees ultimately pass their final exams.

Maguire and her colleague Katherine Woollett, also from University College London, conducted periodic Magnetic Resonance Imaging (MRI) scans and memory tests throughout the training period. Before the taxi drivers began memorising the information, trainees showed no difference in brain structure or learning ability. By their final examinations several years later, however, those 39 who qualified had larger posterior hippocampi than those who failed the tests or controls who were not training for exams. Trainees who passed spent about twice as much time on average studying than those who failed.

Because the changes were very subtle, using another imagining method to confirm the results would ensure that the observed pattern was real, said University of New South Wales neuroscientist Michael Valenzuela from Sydney, who was not involved in the study.

How the Brain Changes

Called neuroplasticity, the ability of the brain to adapt to its environment has been observed in a number of studies over the past decade. Henriette van Praag from the U.S. National Institute on Ageing found that exercise triggered the formation of new neurons in the hippocampi of mice, which coincided with increased memory and learning abilities. The work, she said, “suggests our behavioural choices have influence over the functionality of our brains”.

Although the mechanism is poorly understood, changes may be due to the more frequent generation of neurons in the hippocampus, one of the few regions in the brain where new neurons are generated. But strengthened connections and increased communication between neurons through synapses may also lead to the increased volume of grey matter scientists have observed.

“The challenge we face is to unravel the exact nature of the dynamic structural alterations and ultimately, to be able to adapt and modulate this knowledge for disease management,” May said.

In any case, these findings should motivate the addition of brain exercises to any workout routine, said Valenzuela. “The bottom line is that everyone needs to keep on learning new things and challenging one’s mind, particularly after retirement, in order to maintain optimal brain health.”

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