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Study shows
changes in London taxi drivers’ brains driven by acquiring the
'Knowledge’ |
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December 2011
Acquiring ‘the Knowledge’ - the complex layout of central London’s 25,000 streets and thousands of places of interest - causes structural
changes in the brain and changes to memory in the capital’s taxi
drivers, new research funded by the Wellcome Trust has shown. The study,
published today in the journal 'Current Biology', supports the
increasing evidence that even in adult life, learning can change the
structure of the brain, offering encouragement for lifelong learning and
the potential for rehabilitation after brain damage.
To qualify as a licensed London taxi driver, a trainee must acquire 'the
Knowledge' of the capital's tens of thousands of streets and their
idiosyncratic layout. This training typically takes between three and
four years, leading to a stringent set of examinations that must be
passed to obtain an operating licence; only around half of trainees
pass. This comprehensive training and qualification procedure is unique
among taxi drivers anywhere in the world.
Previous studies of qualified London taxi drivers, led by Professor
Eleanor Maguire from the Wellcome Trust Centre for Neuroimaging at UCL
(University College London), have shown a greater volume of grey matter
- the nerve cells in the brain where processing takes place - in an area
known as the posterior hippocampus and less in the anterior hippocampus
relative to non-taxi drivers.
The studies also showed that although taxi drivers displayed better
memory for London-based information, they showed poorer learning and
memory on other memory tasks involving visual information, suggesting
that there might be a price to pay for acquiring the Knowledge. The
research suggested that structural brain differences may have been
acquired through the experience of navigating and to accommodate the
internal representation of London.
To test whether this was the case, Professor Maguire and colleague Dr
Katherine Woollett followed a group of 79 trainee taxi drivers and 31
controls (non-taxi drivers), taking snapshots of their brain structure
over time using magnetic resonance imaging (MRI) and studying their
performance on certain memory tasks. Only 39 of the group passed the
tests and went on to qualify as taxi drivers, giving the researchers the
opportunity to divide the volunteers into three groups for comparison:
those that passed, those that trained but did not pass, and the controls
who never trained.
The researchers examined the structure of the volunteers' brains at the
start of the study, before any of the trainees had begun their training.
They found no discernible differences in the structures of either the
posterior hippocampus or the anterior hippocampus between the groups,
and all groups performed equally well on the memory tasks.
Three to four years later - when the trainees had either passed the test
or had failed to acquire the Knowledge - the researchers again looked at
the brain structures of the volunteers and tested their performance on
the memory tasks. This time, they found significant differences in the
posterior hippocampus - those trainees that qualified as taxi drivers
had a greater volume of grey matter in the region than they had before
they started their training.
This change was not apparent in those who failed to qualify or in the
controls. Interestingly, there was no detectable difference in the
structure of the anterior hippocampus, suggesting that these changes
come later, in response to changes in the posterior hippocampus.
On the memory tasks, both qualified and non-qualified trainees were
significantly better at memory tasks involving London landmarks than the
control group. However, the qualified trainees - but not the trainees
who failed to qualify - were worse at the other tasks, such as recalling
complex visual information, than the controls.
"The human brain remains 'plastic', even in adult life, allowing it to
adapt when we learn new tasks," explains Professor Maguire, a Wellcome
Trust Senior Research Fellow. "By following the trainee taxi drivers
over time as they acquired - or failed to acquire - the Knowledge, a
uniquely challenging spatial memory task, we have seen directly and
within individuals how the structure of the hippocampus can change with
external stimulation. This offers encouragement for adults who want to
learn new skills later in life.
"What is not clear is whether those trainees who became fully fledged
taxi drivers had some biological advantage over those who failed. Could
it be, for example, that they have a genetic predisposition towards
having a more adaptable, 'plastic' brain? In other words, the perennial
question of 'nature versus nurture' is still open."
In the research paper, Professor Maguire and Dr Woollett speculate on
the biological mechanisms that may underpin the changes to the brain
they observed.
One theory, supported by studies in rodents, is that when learning that
requires cognitive effort takes place and is effective, there is an
increase in the rate at which new nerve cells are generated and survive.
The hippocampus is one of the few brain areas where the birth of new
nerve cells is known to take place. Alternatively, it could be that the
synapses, or connections, between existing nerve cells grew stronger in
the trainees who qualified.
Dr John Williams, Head of Neuroscience and Mental Health at the Wellcome
Trust, says: "The original study of the hippocampi of London taxi
drivers provided tantalising hints that brain structure might change
through learning, and now Eleanor's follow-up study, looking at this
directly within individual taxi trainees over time, has shown this is
indeed the case. Only a few studies have shown direct evidence for
plasticity in the adult human brain related to vital functions such as
memory, so this new work makes an important contribution to this field
of research."
Article and image by kind permission of the Wellcome Trust
www.wellcome.ac.uk
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