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

• Brain scanning is used to study brain structure (i.e. what the brain is, its composition) and function (i.e. what the brain does, its activity)
• 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 (see below):

This type of machine is used for CT, PET and fMRI scanning.

Evaluation of CT scans

Strengths

• CT scans produce much more detailed images than traditional X-rays which means that they are hugely useful for detecting brain abnormalities
• A CT scan can focus on a small area of the body (e.g. the brain), providing only relevant information to the researcher

Weaknesses

• 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 produce a moving picture of the brain
• The tracer attaches to glucose molecules and – due to its bright intensity- can show which areas of the brain are active during a task
• 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

Evaluation of PET scans

Strengths

• A PET scan 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

   Weaknesses 

• 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

• fMRI measures the energy released by haemoglobin and is 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

Evaluation of fMRI

Strengths 

• 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

Weaknesses

• fMRI is slow, having a 5-second delay between brain activity and measurement so it may miss some important information
• It is an expensive procedure so its use is limited and may vary according to a hospital or research institute’s budget