Maguire

Question 1

Hippocampus

Answer 1

Located in medial temporal lobe-makes up part of limbic system(set of brain structures that support variety of functions including emotion and long term memory.
Humans & mammals have 2 hippocampi, one on each side of brain-plays important role in memory.
Hippocampus role is to facilitate spatial memory (navigation).

Question 2

Localisation

Answer 2

Particular brain structure to a particular brain function.

Question 3

Plasticity

Answer 3

Brains ability to change in response to environment and use.

Question 4

Context

Answer 4

In a review of research into hippocampal variations in nature, Lee et al (1998) found that the hippocampus in both birds and mammals, unlike most brain tissue, retains its ability to make new cells, so when seasonal behaviours occur that use the hippocampus, it changes, growing more cells and increasing in volume.

Question 5

Hypothesis

Answer 5

The hippocampi in London taxi drivers will be structurally different to the hippocampi in non-taxi drivers.

Question 6

Aims

Answer 6

• To investigate whether there was a difference in hippocampal volume between individuals who did or did not have extensive navigational experience.
  1) To investigate the role of the hippocampus in navigational spatial skills, and the extent to which the brain shows changes (plasticity) when exposed to navigational experience as demonstrated by London taxi drivers.
  2) Also, to see if there is a correlation between length of taxi driving experience and measure of grey matter volume.

Question 7

Participants: Experimental group

Answer 7

16 right handed males, licensed taxi drivers in London.
Aged 32-62 (mean 44 years old)
All had had their licenses for at least 1.5 years (ranged from 1.5-42 years) mean 14.3 years.
They all had healthy medical profiles.

Question 8

Participants: Control group

Answer 8

50 NON-taxi drivers, male, right handed.
Matched on age range (32-62 years old) mean age of 44.
The scans of the 50 ps in the control condition were selected from the structural MRI scan database at the same unit where the taxi drivers were scanned.
Ps below 32 years old and above 62 years old were EXCLUDED. As well as females, left handed males, and any with health problems.

Question 9

Method & Design

Answer 9

Natural/ Quasi experiment-cannot manipulate IV (taxi driver or non-taxi driver)
Matched pairs design/Independent measures design.
Correlational analysis was carried out to see if hippocampal changes increased with time as taxi driver, and were therefore likely to be environmentally determined.

Question 10

IVs

Answer 10

Taxi driver brain (London)
Non-taxi driver brain (London)

Question 11

DVs

Answer 11

Structure & volume of hippocampi.
Comparison of analysis of MRI scans.

Question 12

Procedure

Answer 12

Data was collected using structural MRI scans, scans were analysed using 2 techniques: VBM (voxel-based morphometry) and Pixel counting.

Question 13

MRI scan

Answer 13

A structural MRI (magnetic resonance imaging) scan involves using a computer software programme to produce a 3D image of the brain.

Question 14

Analysing the MRI scans:
1st Technique- Voxel Based Morphometry
(VBM)

Answer 14

Measures volume of areas of the brain (grey matter).
A voxel is a 3D measurement of volume that allows a computer to calculate the volume of area, in this case the grey matter in the brain in the structural MRI scans.
Grey matter has dense neural connections and is associated with higher order thinking.

Question 15

Analysing the MRI scans:
2nd Technique- Pixel counting

Answer 15

A pixel= a single point on a graphic image.
Person counting the pixels was blind to whether ps were taxi driver or control (non-taxi driver).
Image analysis technique produces 2D measurement of area.
In order to calculate hippocampal volume, pixels were counted on photographix ‘slices’ made through the brain using an MRI scan.
Pixels were counted for the anterior, posterior and body of hippocampus.

Question 16

Controls

Answer 16

-ps were all scanned using same scanner.
-hippocampal volume for each ps was calculated to include an adjustment for the size of each person’s brain, this was to ensure that all ps data was comparable.

Question 17

RESULTS

Answer 17

-VBM showed there was significantly MORE grey matter volume found in taxi drivers brains than control group, in the right and left hippocampus only (not anywhere else in brain).
-This was found only in the posterior hippocampus.
-Taxi drivers had LARGER posterior hippocampus but SMALLER anterior hippocampus.
-There were NO overall differences in pixel count.

Question 18

Correlations

Answer 18

(Data was correlated between time as taxi driver and volume of hippocampus)
POSITIVE CORRELATION- found only in right posterior hippocampus. i.e longer working as a taxi driver=greater volume of grey matter.
NEGATIVE CORRELATION- found between anterior hippocampus and time spent as taxi driver. i.e longer working as taxi driver= less volume of grey matter.
This indicates a REDISTRIBUTION of grey matter in hippocampus.

Question 19

Conclusions

Answer 19

Maguire states ‘professional dependence on navigational skills in licensed london taxi drivers is associated with a relative redistribution of grey matter in hippocampus.

The structure of the brain changes(shows PLASTICITY) in response to; environmental demand and stimulus (i.e effects of ‘the knowledge’).

Taxi drivers had larger posterior hippocampi and smaller anterior.

A basic spatial representation on London is established in the taxi drivers by the time ‘The knowledge’ is complete.
This representation of the city is much more extensive in taxi drivers than in the non-taxi drivers.

Among the taxi drivers, there is, over time and with experience, a further fine-tuning of the spatial representation if London, permitting increasing understanding of how routes and places relate to each other.

Mental map of London is stored in the posterior hippocampi, as this is fine-tuned the posterior hippocampus becomes larger.

The posterior hippocampus stores a spatial memory of the environment and so in the London taxi drivers, the volume of the posterior hippocampus expanded due to their high use of navigational skills.

Question 20

The anterior and posterior hippocampi have different roles:

Answer 20

Posterior: involved when previously learned spatial info is used.
Anterior: more involved during encoding of new environmental layouts.

Question 21

Correlation suggests:

Answer 21

This is a results of being taxi driver, not pre existing structure which predisposes a person to become a taxi driver.
Hippocampus is an old part of brain that may have evolved to deal with navigation.
Undoubtedly, in humans, the functions of the hippocampus have adapted to accommodate other types of memory, but the hippocampus retains an ability to store large-scale spatial info.
The LEFT hippocampus size does NOT correlate with length of time as taxi driver, but posterior is still higher in taxi drivers, so probably stores memories which don’y require spatial elements such as faces.

Question 22

Practical application:

Answer 22

This plasticity is useful for rehabilitation of brain injured patients as it suggests that brain structures can be altered.