- An MRI Scan (Magnetic resonance imaging) subjects people to a strong magnetic field which is turned off and on rapidly in the presence of a radio wave. The atoms of the brain change their alignment because of the magnetic field when it is on and produce characteristic radio signals when it is turned off. A detector reads those signs and can map the structure of the tissue.
- 'The knowledge' is a requirement for taxi-drivers. It is a thorough knowledge of London, including the location of streets, squares, clubs etc. Everything you need to know to be able to take passengers to their destinations by t the most direct routes.
- Past research has indicated that the hippocampus plays a role in spatial memory. i.e. the ability of humans and animals to remember locations and navigate between them.
- Small mammals requiring spatial memory have an increased hippocampal volume
- Hippocampal volume increases in some species where the demand for spatial ability is great.
- There are structural differences in healthy human brains.
1 of 8
- To demonstrate that the hippocampus is the region of the human brain associated with spatial memory and naviation
- There are several unanswered questions
- 1) Are brain differences predetermined or is the brain capable of changing in response to environmental stimulation
- 2) What is the precise role of the hippocampus?
- 3) Does the human brain respond to expeirences requiring spatial memory in the same way as smaller mammals?
2 of 8
Procedure, Method and Sample
- 16, Right-handed, Male, London Taxi Drivers, licensed for more than 1.5 years, with the knowledge, and a mean age of 44. (32-62)
- Even spread of particpants in each age group. They all had healthy medical, neurological and psychiatric profiles.
- Control group of 16 men who were not taxi-drivers. They were age matched to the experimental group.
- Data was collected using structural MRI scans
- Voxel-based morphometry. This technique enables every point of the brain to be examined in an objective and unbiased way. VBM identifies differences in the density of grey matter. 'Grey matter' describes some parts of the brain - there is grey and white matter. Grey matter lies on the surface of the brain and also deep inside in places like the hippocampus. It is the parts of the brain that are the most dense in neural connections and therefore associated with high order thinking
- Pixel-counting. Calculates hippocampal volume. The pixels were counted in the images produced by the MRI scans. Each scan was of a photogenic slice made through the hippocampal region of the pps brains. At least 26 slides. Each slice was 1.5mm, therefore covering a total length of 4 cm.
The images were analysed by one person experienced in the technique who counted the pixels in each slice. This person was blind to whether the pp was a control or not and the VBM findings.
A correlation could be made in relation to total intercrainial volume.
3 of 8
- IV (occupation) was naturally varying
4 of 8
- Density of grey matter in the brain
- Ratio of hippocampal volume
5 of 8
- Occupation of the participant
6 of 8
- In the controls there was increased grey matter in the anterior hippocampus
- In the taxi drivers there was increased grey matter in the posterior hippocampus
- Taxi driver had a larger posterior hippocampus than the controls
- Controls had a larger right side than on the left.
- Controls anterior right hippocampus had a greater volume than in taxi driver
- Time spent as a taxi-driver positively correlated the the volume of the right posterior hippocampus and negatively correlated with the volume of the anterior hippocampus.
7 of 8
- Results suggest a relationship between navigational skills and the relative distribution of grey matter in the hippocampus
- Implies 'nurture' over 'nature'
8 of 8