Two Key Studies of Neural Networks & Neural Pruning: Maguire (2000) & Draganski et al. (2004) (DP IB Psychology)

Key Study 1: Maguire (2000)

Aim: To investigate how neural networks form as a result of spatial navigation in London black cab taxi drivers

Participants: 16 healthy, right-handed male London black cab taxi drivers who had passed ‘The Knowledge’, a test of spatial navigation, aged 32-62 years with a mean age of 44 years. They had all been taxi drivers for at least 18 months, with the highest number of years as a taxi driver at 42 years

Procedure: The participants were placed in an MRI scanner and their brains were scanned. The MRI measured the volume of grey matter in the hippocampus of each participant, and this was then compared to pre-existing scans of 50 healthy, right-handed males (the control group). The grey matter was measured using voxel-based morphemetry (VBM) which focuses on the density of grey matter and pixel counting

Results: The posterior hippocampi of the taxi drivers showed a greater volume of grey matter than that of the controls, who had increased grey matter in their anterior hippocampi compared to the taxi drivers. Maguire also carried out a correlational analysis which showed a positive correlation between the volume of posterior hippocampal grey matter and the length of time spent as a taxi driver

Conclusion: The posterior hippocampus may be linked to spatial navigation skills due to a specific neural network of cells within the posterior hippocampus

Evaluation of Maguire (2000)

   Strengths

• The study used a highly controlled clinical method of obtaining objective data which could then be easily compared and analysed

• The correlational analysis of time spent as a taxi driver linked to increased volume of hippocampal grey matter lends validity to the idea that neural networks form as a result of  learning and experience

   Limitations

• A correlation cannot show cause-and-effect so it is impossible to know whether the taxi drivers already had naturally high levels of hippocampal grey matter

• Neural networks may have formed in the participants’ brain due to other, unknown factors

Key terms:

• Spatial navigation  

• Posterior hippocampus

• Neural networks

Key Study 2: Draganski et al. (2004)

Aim: To investigate whether structural changes in the brain would occur in response to learning and then ceasing juggling.

Participants: A self-selected sample of 24 adults aged 20-24 years old (21 female; 3 male) with no prior experience of juggling.

Procedure: The participants were randomly allocated to 2 conditions: jugglers or non-jugglers. Each participant underwent an MRI scan. Those in the juggling condition were taught a 3-ball cascade juggling routine. They were asked to practice this routine and to notify the researchers when they had mastered it. At that point the jugglers had a second MRI scan. After this second scan they were told not to juggle anymore and then a third and final scan was carried out 3 months later. The non-jugglers also underwent 3 separate MRI scans at pre-determined intervals. 

Results: The MRI scans showed that there was no difference in grey matter in the brains of jugglers and non-jugglers at the time of the first scan (before the juggling practice began). At the end of the first part of the study, when the jugglers had been practising juggling, they had a significantly larger volume of grey matter in their mid-temporal cortex in both hemispheres (an area of the brain associated with visual memory, co-ordination, and movement).

Three months after the jugglers had stopped juggling the amount of grey matter in this region had decreased. However, the jugglers still had more grey matter after the study than at their first scan. The non-jugglers’ brains showed no changes at all from first to final scan.

Conclusion: Grey matter appears to increase in specific brain regions (neuroplasticity) in response to environmental demands (learning to juggle) and shrinks in the absence of that learning (stopping juggling). Thus, this study provides evidence for both neuroplasticity and neural pruning (and neural networks as it is via these that the learning takes place).

Evaluation of Draganksi et al. (2004)

   Strengths

• This study has good internal validity as it took baseline measurements of the participants before the process began so as to ensure that real changes could be observed for comparison

• The findings have a useful application as they can be used to inform possible interventions and therapies to offset degenerative brain conditions such as Alzheimer’s

   Limitations

• This was a self-selecting sample which means that it is not representative of a wider population as self-selecting samples often share characteristics e.g. helpful, interested, extrovert

• The participants were not in controlled conditions when they were learning to juggle so some of them may have over-practised, under-practised or not practised at all which would mean that the neural growth and pruning was due to other factors

Key terms:

• Mid-temporal cortex  

• Visual memory  

• Structural changes