Navigation-related structural change in the hippocampi of taxi drivers
Maguire et al (2000)
This study investigated the differences between the hippocampi of taxi drivers and a control group of non-taxi drivers. This was to see whether the hippocampi, which are linked to navigation and spatial awareness, were different in London taxi drivers. The researchers used two different analysis techniques to measure the volume of the left / right anterior and posterior hippocampi in 16 London taxi drivers, all male, aged between 32 and 62. The results showed that the taxi drivers had a larger posterior hippocampus, whereas the control group had a larger anterior hippocampus. There was also a correlation between the size of the right posterior hippocampi and length of time spent as a taxi driver. The results suggest that the volume of the hippocampus changes relating to environmental stimuli, indicating that this region of the brain has plasticity and differences are acquired.
- 16 right handed, male, licensed London taxi drivers, mean age 44 yrs, range 32-62 yrs who had all been taxi drivers for at least 1.5 yrs (mean 14.3 yrs, range 1.5-42 yrs). All had good general health.
- Control group consisted of 50 scans taken from the MRI database where the taxi drivers were scanned, after excluding females, left-handed males, those not aged 32-62 and those with any health problems. The mean age and age range were the same as for the taxi drivers and the ages were also spread across the whole range.
Measurement and AnalysisData was collected using images from Structural MRI scans which create a three-dimensional sequence of 108 images (slices of 1.5 mm).
VBM analysis was based on voxels (3D pixels) of 1.5X1.5X1.5 mm. Each image was standardised to a template image to adjust for differences in overall brain size. The template was based on 50 healthy males scanned on the same scanner (13 of which were in the control group). The images were then separated into gray matter, white matter and cerebrospinal fluid, then the gray matter images were smoothed to reduce the confounding effect of differences in brain anatomy. The gray matter of the taxi drivers was then compared to the control group based on a standard definition of the different hippocampal regions. Differences were analysed statistically using a t test and linear model (p<0.05).
Pixel Counting also used the standard definition of the different hippocampal regions and the images of the taxi drivers were compared to 16 of the control group of exactly the same ages. 26 slices for each hippocampus (left and right) of each subject were analysed by a person experienced in using the MRI technique who did not know whether the images were from the experimental or control group. The 2 most posterior slices were excluded due to variance, leaving 24 slices: 6 posterior, 12 body and 6 anterior. The total volume for each area of the hippocampi was calculated by counting the pixels in each slice and then multiplying this by the depth of the slice (1.5mm). The data was corrected for differences in ICV (intracranial volume – overall brain size).
Changes with Navigational Experience was measured by correlating the length of time in months spent as a taxi driver against the amount of gray matter measured in both techniques.