Maguire et al

• Background:

  Research has shown increased hippocampal volume relative to brain and body size in small mammals and birds who show behaviour requiring spatial memory e.g. food storing.

  In some species, hippocampal volumes enlarge specifically during seasons when spatial ability is greatest.

  Research has also shown that there are differences in the structure of healthy human brains e.g. between males and females, musicians and non-musicians.
• Background pt2:

  However past research has not shown:

  Whether differences in brain structure is susceptible to plastic change in

  response to environmental stimulation.

  The precise role of the hippocampus in humans.

  Whether the human brain responds to experiences requiring spatial memory

  in the same way as smaller mammals and birds.

  Maguire therefore aimed to show that the hippocampus in the human brain

  is the structure associated with spatial memory and navigation.
• Aim: To investigate whether there was a difference in hippocampal volume between individuals who did, or did not have extensive navigational field.
• Research design:

  quasi/natural experiment

  independent measures

  matched participants
• Sample:16 right handed male licensed taxi driversControl group of 16 non-taxi drivers, matched on age range of taxi drivers

  Mean age 44 (range 32-62 years)
• IV: whether the participant was a London taxi driver or a person who did not drive taxis was naturally varying and so could not be manipulated or controlled by the researchers
• DV: the volume of the hippocampi including their anterior, body and posterior regions; measured by analysing MRI scans of participants’ brain using the two techniques of VBM and pixel counting.
• Method:

  The MRI scans of all participants were analysed using: VBM (voxel-based morphometry) which is an automatic procedure that ‘normalises’ the scans to a template to eliminate overall brain size as a variable and then identifies differences in grey matter density in different regions of the brain. The brains of the 16 taxi drivers were compared to those of 50 non-taxi drivers to see if there were any differences in structure.
• Method pt2:

  Pixel counting compared the volume of anterior, body and posterior cross-sections of the taxi drivers’ hippocampi with those of a previously age, gender and handedness-matched sample of 16 controls taken from the 50 used in the VBM analysis. The images were analysed by one person experienced in the technique and blinded to whether the scan was of a taxi driver or a control and the VBM findings. This procedure allowed the total hippocampal volume to be calculated
• Results:

  • VBM analysis showed no significant differences between the brains of the two groups except: Taxi drivers had significantly increased grey matter volume in the right and left posterior hippocampi compared to controls.
  • In the controls there was a relatively greater grey matter volume in the right and left anterior hippocampi compared to taxi drivers.
  • Pixel counting showed that although there was no significant difference in overall volume of the hippocampi between the two groups: Taxi drivers had a significantly greater posterior hippocampal volume than controls.
• Results pt2:

  • Controls had a significantly greater anterior right hippocampal volume than the taxi drivers.
  • A significantly greater hippocampal body volume on the right than the left in both the taxi drivers and the Controls
• Conclusion:

  • There are regionally specific structural differences between the hippocampi of licensed London taxi drivers compared to those who do not drive London taxis.
  • The professional dependence on navigational skills in licensed London taxi drivers is associated with a relative redistribution of grey matter in the hippocampus.
• Conclusion pt2:

  • It can be suggested that the changes in the arrangement of hippocampal grey matter are acquired i.e. due to nurture.
  • Findings also indicate the possibility of local plasticity in the structure of a normal human brain which allows it to adapt in response to prolonged environmental stimuli.