Background Information

The MRI was invented in 1977 and was a major breakthrough in brain research. MRIs can be used for any part of the body and you may have even had one yourself if you’ve suffered from an injury. However, in psychology they are used to study the brain and this is what our focus will be on.

MRIs use magnetic fields and radio frequency[1]. Because of the extreme magnets, MRIs are dangerous for people who have metal inside their bodies (e.g. screws or plates in their knees) as the magnet could cause severe pain to the person.

What does an MRI measure?

Images from an MRI machine show cross-sections, or “slices” of the brain. The images from an MRI allow researchers to see the structure of the brain, i.e. what it looks like. For example, if someone has a brain tumour growing inside their skull, the MRI will show this. Similarly, if people are missing parts of their brain, this will show up as an empty black space in the MRI images.

MRIs are often used in natural experiments where two groups are compared. These may be people who are suffering from a psychological disorder, such as Alzheimer’s or PTSD and they are compared with “control” groups. For example, the MRI can show the extent of the atrophy[2] in an Alzheimer’s patient in the image to the right compared with a healthy control subject. Other studies have also shown differences in brain development between children who have been severely neglected and those who have not.[3]

Maguire’s research used MRIs to compare the differences in brain structures between London bus drivers and taxi drivers.[4]

            There has also been extensive research on people with PTSD using MRI scanners. The PTSD subjects and the controls brains are scanned and their differences are noted. Results from these types of studies show that the hippocampi in people with PTSD are actually smaller than the healthy control subjects.
So does this show that a small hippocampus may be the cause of PTSD? Being able to answer questions like these regarding MRI use and research are really important to fully understand the limitations of using MRIs in psychological research.

An MRI machine

Here you can see how a bunch of images from MRI scans can be put together to form a 3D image. Can you recognize any areas of the brain?

Here you can see just how dangerous the magnets in MRIs can be if you are not careful to avoid putting any metal near MRIs.

Examples of Research:

  • Maguire’s study comparing London taxi driver with bus drivers (See Key Study Description)
  • Perry’s study comparing brain development of neglected children with “normal” children (Revision Text, p10)
  • Comparative studies of PTSD patients (see above)

Key Questions

  1. What do the scanned images from an MRI show?
  2. Why do studies with MRIs often use the natural experimental method?
  3. What are the strengths and limitations of using MRI scans?
  4. What is the relationship between brain structure and behaviour as shown in the results of one study using MRI?

Extension Critical Thinking Questions

  • How did one study use an MRI to investigate (and demonstrate) relationships between the brain and behaviour? (Application)
  • What are the fundamental differences between an MRI and an fMRI? (Analysis)
  • What are the strengths and limitations of using MRIs to investigate relationships between the brain and our behaviour? (Evaluation)



Hannibal, Jette. Crane, John. Psychology. Course Companion. Oxford Press. UK. 2009

Law, Alan et al. Psychology: Developed Specifically for the IB Diploma. 2010.

[1] See the blog and the Pearson Textbook p41 for more information on how exactly MRIs work.

[2] Wasting away and shrinking of a muscle or organ, in this case the brain

[3] Perry’s research in the Revision Text, p10.

[4] For more information see the “Key Study Description” handout.