Techniques used to Study the Brain: fMRI and PET
What is fMRI?
- Functional Magnetic Resonance Imaging (fMRI) measures oxygenated blood flow in the brain i.e. brain activity
- Oxygenated blood has a different resonance than deoxygenated blood: more active areas of the brain receive more oxygenated blood
- A computer transforms the information into a brightly coloured 3D image which is mapped using voxels (each voxel = thousands of neurons)
What is PET?
- Positron Emission Tomography (PET) uses a radioactive tracer to measure glucose metabolism of specific regions in the brain
- The tracer used in PET attaches to glucose molecules and – due to its bright intensity- can show which areas of the brain are active during a task
- If cells require more energy they will burn more glucose and this is what is shown in the scan
Which studies use PET?
- fMRI was used by Fisher et al. (2003) in her study of the link between romantic love and dopaminergic activity in the brain
- PET was used by Raine et al. (1997) to investigate the role of the prefrontal cortex in the brains of impulsive murderers
Both of these studies are available as separate Key Studies – just navigate the Brain and Behaviour section of this topic to find them.
Examiner Tip
fMRI and PET scans are interpreted according to the intensity and brightness of the image: the areas in ‘fiery’ colours such as red, orange and yellow indicate the highest levels of activity (with red showing the most activity) while the ‘cooler’ colours such as blue, green and black indicate very little or no activity.
What are the strengths and limitations of fMRI?
Strengths:
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- It enables researchers to measure oxygenated blood in specific brain regions which can inform them of brain activity linked to cognitive processes such as emotion
- It does not use radiation (unlike PET) so it is a non-invasive procedure
Limitations:
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- fMRI is slow, having a 5-second delay between brain activity and measurement and so it may miss some important information
- It is an expensive procedure (as is MRI) so its use is limited and may vary according to a hospital or research institute’s budget
What are the strengths and limitations of PET?
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- Strength: It is more sensitive than other scanning techniques and can highlight abnormalities and illness more successfully
- PET scans are not affected by small movements which makes it an easier procedure for the patient to endure
Limitations:
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- Using a radioactive tracer involves some risk to the patient
- The images produced by a PET scan are not as clear as those produced by fMRI
Examiner Tip
You might want to think about including some critical thinking on culture into a 22-mark question on the use of brain-imaging technology such as fMRI and PET. It may be that some collectivist cultures do not agree with modern technologies as a way of diagnosing illness (particularly mental illness) which would mean that the use of these techniques might be problematic in some cultures.
