Psychology - Maguire et al. (2000)

Maguire et al. (2000)

 

The hippocampus:

 

• Located in the medial temporal lobe.
• One on left, one on right side.
• Major function is to do with memory and spatial navigation.
• Argued that after a time, some memories are moved from the hippocampus to another part of the brain after it has been consolidated.
• Damage to hippocampus = inability to form new memories but previous memories are often spared.
• Gage

 THE ROLE IN NAVIGATION:

-Small mammals and birds that rely heavily on navigation have a much larger hippocampus relative to body size than those that rely less on it.

-Animals and birds have larger hippocampi during migration seasons than at other tie – plasticity.

-Neurons in hippocampus have spatial firing cells which fire when an animal finds itself in a particular location.

-Place cells have also been found in humans involved in finding their way around a virtual-reality town.

Aim of the study:

·        To determine whether changes could be detected in the brains of humans who have extreme experiences of spatial navigation.

Participants:

·        16 male black-cab drivers who had passed “the knowledge”.

·        All were right-handed

·        Aged between 32 and 62 (mean age – 44)

·        Licensed for at 18 months to 42 years (mean – 14.3 years)

·        Average time taken to pass the knowledge was 2 years.

·        All healthy medically, neurologically and psychiatrically.

CONTROL

·        50 MRI scans from the structural MRI scan database @ same centre cab drivers were scanned.

·        Healthy, right-handed males

·        Similar ages

Method:

• Quasi
• Data collected from 2 techniques of analysing MRI scans – Voxhel-based morphology & pixel counting.

VOXHEL-BASED MORPHOLOGY

-Voxhel represents the image in 3-D

-used to identify changes in a variety of neurological disorders, including schizophrenia and temporal lobe epilepsy.

-Also been used to identify structural abnormalities such as those found in patients with Alzheimer’s and multiple sclerosis.

PIXEL COUNTING

-Pixel represents the image in 2-D

What is an MRI scan?

·        Magnetic resonance imaging

·        Aligns atomic particles in body tissues by magnetism, then bombards them with radio waves.

·        This causes the particles to give off radio signals that differ depending on what type of tissue is present.

·        Computer software then converts this into a 3-D image of a greyish x-ray.

Results:

•  Analysis using VBM showed brains of cab drivers had significantly increased grey matter volume in right and left hippocampi.
• Difference was found in posterior hippocampus only.
• Control group had relatively larger grey matter volume in anterior relative to cabbies.
• No other differences found between 2 groups.
• Pixel-counting showed no significant difference in overall volume of hippocampi but confirmed regional differences as VBM showed.
• Volume of right hippocampus showed a positive correlation with the length of time as a cab driver, negative correlation in left side.
• Also a correlation between volume of posterior hippocampus and length of time as a cab driver in right side.

Conclusions:

•  Results suggest evidence of differences between hippocampi of licensed cab drivers and control group.
• Also suggest that more experience = larger volume of posterior hippocampus.

Evaluation:

 STRENGTHS:

-Quantitative data

-Used precise measuring equipment

-Unlikely to be subject to bias

-No demand characteristics

-MRI scans are safe.

-High control (No right-handed people or women)

WEAKNESSES:

-difficult to draw conclusions from quasi experiments as extraneous variables may have been involved.

-MRI not suitable for patients with pacemakers or metal plates.

-Children may not lie still

-Unsuitable for claustrophobics

REPRESENTATIVENESS:

-Cab drivers are not representative of general population, but researchers were not trying to apply the results to whole population.

-Good choice of cab drivers – all had good navigational skills in one particular area.