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SAQ sample: Neural pruning

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  • SAQ sample: Neural pruning

The following sample is for the question: Explain neural pruning with reference to one study.  

The sample below is an exemplary response.

What is this question asking?

  • The focus of the question is on an explanation of neural pruning. There should be a clear understanding of the process demonstrated.
  • A relevant study should be described in terms of the aim, procedure, and findings.
  • There should be an explicit explanation of what the study teaches us about neural pruning.

Sample response

Neuroplasticity is the process by which our brains adapt to changes in the environment.  One of the ways that our brains change is through the creation of neural networks. This happens because of long-term potentiation - that is, the repeated firing of neurons.  This leads to an increase in dendritic branching which leads to an increase in the number of synapses.  Another way that our brain can change is through neural pruning - which is a decrease in the number of synapses as a result of the removal of dendritic branches. Pruning can be the result of neuron cell death, hormones such as cortisol or the lack of use of a neural pathway.  The exact mechanism of neural pruning is not yet fully understood.

A study by Draganski showed that when neural pathways are not used, they may be pruned.  The sample was made up of 24 non-jugglers.  Each participant had an MRI scan at the beginning of the study in order to see the structure of the brain prior to the experiment.  The participants were randomly allocated to one of two conditions.  In one condition, they were asked to learn a juggling routine and to practice it daily until they had mastered it. When they did, they had a second MRI. Then they were told not to juggle anymore.  Three months later they had a third MRI.  The other group of participants simply served as a control group.

Using voxel-based morphometry the researchers measured the density of the grey matter in the brains of jugglers vs. non-jugglers. The jugglers showed a significantly larger amount of grey matter in the mid-temporal area in both hemispheres - an area associated with visual memory. Three months after the participants stopped juggling, the amount of grey matter in these parts of the brain had decreased.

This shows that when learning a new skill, new neural networks were created.  However, when the behaviour stopped and those neurons were no longer activated, the neurons were pruned.  Researchers hypothesize that neural pruning is a way to increase the efficiency of the brain.

347 words

What are common problems with answering this question?

  • There is only a limited explanation of neural pruning.
  • The study is not focused on neural pruning, but on the localization of function.
  • The study is not clearly described in terms of the aim, procedure, and findings.
  • There is no clear explanation of what the study teaches us about neural pruning.