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Navigation-related structural change in the hippocampi of taxi drivers
1. Eleanor A. Maguire*†,
2. David G. Gadian‡,
3. Ingrid S. Johnsrude†,
4. Catriona D. Good†,
5. John Ashburner†,
6. Richard S. J. Frackowiak†, and
7. Christopher D. Frith†
+ Author Affiliations
1. †Wellcome Department of Cognitive Neurology, Institute of Neurology, University CollegeLondon, Queen Square, London WC1N 3BG, United Kingdom; and ‡Radiology and Physics Unit, Institute of Child Health, University College London, London WC1N 1EH, United Kingdom
1. Communicated by Brenda Milner, McGill University, Montreal, Canada (received for review November 10, 1999)
 
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Abstract
Structural MRIs of the brains of humans with extensive navigation experience, licensedLondon taxi drivers, were analyzed and compared with those of control subjects who did not drive taxis. The posterior hippocampi of taxi drivers were significantly larger relative to those of control subjects. A more anterior hippocampal region was larger in control subjects than in taxi drivers. Hippocampal volume correlated with the amount of time spent as a taxi driver (positively in theposterior and negatively in the anterior hippocampus). These data are in accordance with the idea that the posterior hippocampus stores a spatial representation of the environment and can expand regionally to accommodate elaboration of this representation in people with a high dependence on navigational skills. It seems that there is a capacity for local plastic change in the structure of the healthyadult human brain in response to environmental demands.
One important role of the hippocampus is to facilitate spatial memory in the form of navigation (1). Increased hippocampal volume relative to brain and body size has been reported in small mammals and birds who engage in behavior requiring spatial memory, such as food storing (2). In some species, hippocampal volumes enlarge specificallyduring seasons when demand for spatial ability is greatest (2, 3). In the healthy human, structural brain differences between distinct groups of subjects (for example, males and females, ref. 4, or musicians and nonmusicians, ref. 5) have been documented. From existing studies, it is impossible to know whether differences in brain anatomy are predetermined or whether the brain is susceptible toplastic change in response to environmental stimulation. Furthermore, although lesion work (6, 7) and functional neuroimaging work (8) confirm the involvement of the human hippocampus in spatial memory and navigation, there is still debate about its precise role. Given the propensity of lower mammalian/avian hippocampi to undergo structural change in response to behavior requiring spatial memory (2, 3),the present study addressed whether morphological changes could be detected in the healthy human brain associated with extensive experience of spatial navigation. Our prediction was that the hippocampus would be the most likely brain region to show changes.
Taxi drivers in London must undergo extensive training, learning how to navigate between thousands of places in the city. This training iscolloquially known as “being on The Knowledge” and takes about 2 years to acquire on average. To be licensed to operate, it is necessary to pass a very stringent set of police examinations. London taxi drivers are therefore ideally suited for the study of spatial navigation. The use of a group of taxi drivers with a wide range of navigating experience permitted an examination of the direct effectof spatial experience on brain structure. In the first instance, we used voxel-based morphometry (VBM) to examine whether morphological changes associated with navigation experience were detectable anywhere in the healthy human brain. VBM is an objective and automatic procedure that identifies regional differences in relative gray matter density in structural MRI brain scans. It allows every...