maguire

• concept of localisation of function illustrates a role of the hippocampus in navigation.

  hippocampus provides a 'cognitive map' - a mental representation of spatial relationships

  previous research documents how the hippocampus changes in volume with use in humans and animals

  neural plasticity - the idea that the brain structure and function can change with experience
• Lee et al (1998) - hippocampus in birds and mammals retains its ability to make new cells. Hippocampus changes, growing more cells and increasing in volume, when seasonal behaviours occur such as homing and catching food
• Smulders et al (1995) - birds such as the black-capped chickadee have their hippocampus increase in volume during the period when they are learning food-store locations.

  suggests that people who make greater use of navigational skills might develop hippocampi with a larger volume
• aim

  to investigate whether there was a difference in hippocampi volume between individuals who did, or did not, have extensive navigational experience
• hypothesis

  the hippocampi in London taxi drivers will be structurally different to the hippocampi in non-taxi drivers
• research method

  laboratory setting

  quasi experiment - ppts already belonged to the existing groups of 'taxi drivers' and 'controls'

  correlational analysis conducted to consider variables of hippocampal volume and time spent as a taxi driver

  IV - london taxi driver brain or non-taxi driver brain

  DV - structure & volume of hippocampi
• participants - experimental group

  16 right-handed male taxi drivers

  mean age 44 years (range 32-62)

  experience as licensed London taxi drivers varied between 1.5 years and 42 years (mean 14.3 years)

  time on knowledge took average of 2 years (range 10 months-3.5 years, some part time and some full time)

  all were medically, neurologically and psychiatrically healthy
• participants - control group

  matched control group of people on the MRI-scan database held at the unit where the experimental ppts were scanned

  females, left-handed males, those under 32 or over 62 and those with health problems were excluded

  scans of 16 people used as non-taxi driving controls
• procedure

  MRI scans of brains of 50 healthy, right handed, male, non-taxi drivers aged 33-61 were analysed to establish a comparison database of 'average hippocampi' - by Voxel Based Morphometry (VBM)

  MRI scans of brains of 16 taxi drivers and 16 matched controls were analysed by VMB and compared to the database of images - expert conducting analysis did not know whether MRI scan was taxi driver brain or not as a control
• findings

  taxi drivers have a higher volume of posterior hippocampi

  longer spent as a taxi driver, the larger the right posterior hippocampus

  taxi drivers had a greater volume in the posterior hippocampus but non taxi drivers had a greater volume in the anterior hippocampus indicating redistribution of grey matter in hippocampus
• conclusion

  structure of the brain changes in response to environmental demand and the mental map of the city of London is stored in the posterior hippocampi
• research method - strength

  scanning procedure was in a highly controlled environment and the sample was carefully selected - eliminates extraneous variables such as the hippocampal volume increasing with age

  laboratory procedures are straightforward to replicate as the controls and standardised procedures make them reliable
• sample - strengths

  age spread, the ranger and the nature of training and time in the job all contributed to a varied sample - matching of experimental to control ppts used several important criteria (age, gender and handedness)
• sample - weakness

  all male right handers which limits generalisability of the findings as navigation by females or left-handed people may differ
• quantitative data - strength

  could be analysed statistically, allowing researchers to be more certain about their conclusions

  measurements of length and volume are objective - reliable and independent of experimenter bias
• ethics - weakness

  ethical issues of informed consent and competence - MRI scanning isn't dangerous but carries risks if ppts have metal implants like pacemakers or pinned bones

  MRI scanner is a confined space and noisy - ppts may find this unpleasant or frightening -> claustrophobic
• ethics - strength

  control ppts were not given unnecessary brain scans as their data was retrieved from an existing store
• reliability - strength

  can be replicated and get the same results -> reliable - hippocampal volumes recorded from brain scans, one experienced individual assessed all of the images
• validity - weakness

  occupation interests of control group were not considered - possible the group included individuals with other reasons for a high demand on navigational skills -> people who go orienteering or drive to lots of places for work
• validity - strength

  lack of ecological validity not an issue - ppts did not have to perform a task but scanner is an artificial environment

  researcher assessing the scans was unaware of ppts' condition increasing validity of DV - less likely to be biased
• practical applications

  identification of brain plasticity in adults had implications for hope of rehabilitating people with brain damage

  study shows that the hippocampus can alter its neural circuitry in adulthood, but suggests other brain areas could too - potential to lead to advances in diagnosis and treatment, identify deterioration that puts people at risk and use environmental demand to encourage redevelopment of brain tissue -> Alzheimer's disease, stroke patients