The Use of Scanning Techniques to Identify Brain Functioning (AQA GCSE Psychology): Revision Note

Brain scanning is used to study brain structure (i.e. what the brain is) and function (i.e. what the brain does)

The three techniques for brain scans are: 

• CT scans (Computerised Axial Tomography) 

• PET (Positron Emission Tomography) 

• fMRI (Functional Magnetic Resonance Imaging) 

CT scans do the following:

• CT scans use an X-ray beam to produce a picture of the brain

• The X-ray beam moves in a circle around the brain which allows many different cross-sectional views of the brain to be seen in great detail

• The X-ray data is sent to a computer that interprets it and displays it in 2D form 

• CT scans can help to diagnose tumours, investigate internal bleeding such as when a stroke has occurred or look for other injuries or damage 

• Having a CT scan involves lying on a bed which is inserted in a long, doughnut-shaped scanner

CT scans produce much more detailed images than traditional X-rays which means that they are hugely useful for detecting brain abnormalities

CT scans are widely available and relatively quick to carry out compared with other scanning techniques

CT scans do not show brain function which means that their use is limited to research involving structural change or features only

CT scans use radiation which means that they cannot be used with the same person too many times

PET scans do the following:

• PET involves injecting the patient with a radioactive tracer to show a picture of brain activity

• The tracer itself is a radioactive substance similar to glucose, which active brain areas absorb more of

• The person in the scanner can be carrying out a specific action while being scanned e.g. pressing a button

• If cells require more energy they will burn more glucose and this is what is shown in the scan

PET scans can show the brain in action, which is useful for psychological research

PET scans are also useful for showing localisation of function

• For instance, the person can be asked to look at a picture, solve a jigsaw puzzle, or think about a memory, and the linked brain area can be identified

PET scans are extremely expensive and are therefore not easily available for research

Results are not always easy to interpret

• Scans of different people doing the same task have shown different patterns of brain activity

Using a radioactive tracer involves some risk to the patient, and ethical concerns around repeated radioactive injections mean the technique can only be used a limited number of times

fMRI measures changes in blood oxygen levels in the brain (this is called the haemodynamic response) and produces a moving picture

It uses large magnets to detect oxygenated (and deoxygenated) blood flow in the brain

The person in the scanner can be carrying out a specific action while being scanned e.g. pressing a button

More active brain areas need more blood flow (this is oxygenated blood)

Inactive or less active parts of the brain show deoxygenated blood

Active areas can then be compared with areas that are lower in activity which are shown on the fMRI image

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

The images produced by fMRI are extremely clear and can show brain activity to the millimetre

fMRI is slow, having a 5-second delay between brain activity and measurement so it may miss some important information

It is only effective if the person being scanned stays perfectly still, which can be a problem for some people, such as children

It is an expensive procedure so its use is limited and may vary according to a hospital or research institute’s budget