Sample 2

Two techniques used to study the brain are magnetic resonance imaging (MRI) and functional magnetic resonance imaging (fMRI). MRIs use magnetic fields and radio waves to map the activity of hydrogen protons. Water molecules contain hydrogen protons and are present in brain tissue. MRIs create composite pictures of brain structures. The images can be viewed from any angle as a slice of the brain, or they can be used to create a three-dimensional image of the brain. Two possible ways to analyse MRIs are voxel-based morphometry (VBM) and pixel counting. VBM can be used to measure the density of grey matter and pixel counting can be used to calculate the area of certain brain structures. Unlike MRIs, which look purely at brain structure, fMRIs show actual brain activity and indicate which areas of the brain are active when engaged in a behaviour or cognitive process. fMRIs measure changes in blood flow as a measurement of brain activity. If a specific part of the brain is active, it requires more oxygen and thus blood flow to that part of the brain increases. fMRIs produce a film that demonstrates the changes in blood flow in the brain (and therefore also neural activity) during the period of the scan.

MRIs were used in a study by Maguire to look at whether the brain structure of London taxi drivers was somehow different as a result of their training and experience. The MRI scans of 16 right-handed male London taxi drivers were compared to the scans of 50 right-handed males who did not drive taxis, which were taken from an MRI database. All the taxi drivers had to have had their license for at least 1.5 years. The study was a single-blind study as the researcher did not know whether she was looking at the scan of a taxi driver or at a control. The density of the grey matter in the brain was measured using VBM and the area of the hippocampi was calculated using pixel counting. Maguire found that the posterior hippocampus of taxi drivers was significantly larger than the hippocampi of the controls taken from the MRI database. From the VBM, a correlation was found between the volume of the right posterior hippocampus and amount of time spent as a taxi driver. Maguire argued that this demonstrates that the structure of the hippocampus may change due to environmental demands.

The use of MRIs in Maguire’s study allowed her to find a correlation between hippocampus structure and environmental demands; however, there was no clear causation established. MRIs only indicate structure, they do not actually map what is happening in the brain.  The non-invasive nature of MRIs means that there was minimal risk of the taxi drivers experiencing undue stress or harm. However, MRIs can still cause anxiety and stress in some people due to the loud sounds the machines make. The resulting images of MRIs have high resolution, which gives the researcher a good sense of the brain.

In a study by Harris & Fiske, fMRI scans were used to investigate the role of the limbic system in reacting to out-groups such as homeless people and addicts. 22 university students were divided into two groups. One group acted as a control and was shown pictures of objects while they were in an fMRI, whereas the other group was shown pictures of people. The participants were then put inside the scanner and were shown six sets of ten photographs. The photographs were of a range of people, from rich business people and Olympic athletes to people with disabilities and homeless people. The researchers found that there was a clear difference in brain activity when the participants rated pictures of people in their ‘extreme out-groups’; in addition to the activation of the amygdala, the insula gyrus which is associated with disgust, was activated. This may show that prejudice is more hardwired than we would like to believe.

The use of fMRIs is very expensive. For Harris & Fiske’s study, this meant that they were only able to have a small sample size. This means that the results may not be generalizable to a larger population and that more research should be done to see if the results are reliable. One of the strengths of the use of fMRIs in Harris & Fiske’s study is that fMRIs do not allow for demand characteristics, as people are not able to control their involuntary brain activity that occurs as a response to an image. However, brain areas do activate for various reasons and we cannot be certain that a person is experiencing disgust when certain parts of the brain light up. Like MRIs, fMRIs are also very loud and many people may feel claustrophobic when they are in the machine. The participants’ reactions to the noise or the claustrophobia may influence the brain activity seen on an fMRI scan.  Despite this, fMRIs create high-resolution images that show brain activity over a period of time, which allowed Harris and Fiske investigate the reactions of people. This would not have been possible with an MRI because no change in brain structure occurred.

Both MRIs and fMRIs are useful techniques for studying the brain. They both are non-invasive and produce high-resolution images or film, however, it is important not to over-interpret the information they provide. Costs limit sample sizes making the reliability of much of the research questionable.

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