Brain-scanning techniques (CAT, PET, and fMRI). The use of brain-scanning techniques to investigate human behaviour, including aggression.
Psychologists use CAT scans to detect whether there are any abnormalities in the brain that may be causing a specific behaviour such as aggression. CAT scans pass multiple X-rays through the brain which are then constructed into a 3D image of the brain by a computer.
CAT scans give objective data as the computer forms an image from the scan, so increasing the reliability of the results from the CAT scan as the results are not subjective.
CAT scans emit radiation which means they can be harmful to some people, therefore they may cause harm to some people such as the foetus if a woman does not know she is pregnant.
PET scans are a type of nuclear medicine imaging which use a small amount of radioactive material to diagnose and determine the severity of brain diseases, including cancers and neurological disorders. PET scans involve the injection of a radioactive tracer; this tracer then appears as a bright colour on the scan, indicating which areas of the brain are most active in metabolising glucose during a task. The brighter the colour, the more active that part of the brain during that particular task
PET scans can not be used on everyone, and some people are allergic to the radioactive tracer. Also, PET scans are not used on children or pregnant women and are therefore unable to measure the relationship between biological factors and behaviour in these groups which is a slight limitation of this technique.
Functional magnetic resonance imaging (fMRI) is a brain-scanning technique that measures blood flow in the brain when a person performs a task. fMRI works on the premise that neurons in the brain that are the most active (during a task) use the most energy. An fMRI creates a dynamic (moving) 3D map of the brain, highlighting which areas are involved in different neural activities.
Energy requires glucose and oxygen. Oxygen is carried in the bloodstream attached to haemoglobin (found in red blood cells) and is released for use by these active neurons, at which point the haemoglobin becomes deoxygenated.
Deoxygenated haemoglobin has a different magnetic quality from oxygenated haemoglobin. An fMRI can detect these different magnetic qualities and can be used to create a dynamic (moving) 3D map of the brain, highlighting which areas are involved in different neural activities. fMRI images show activity approximately 1-4 seconds after it occurs and are thought to be accurate within 1-2 mm. An increase in blood flow is a response to the need for more oxygen in that area of the brain when it becomes active, suggesting an increase in neural activity.
fMRI scans take scans of a functioning brain by placing the head in a scan that uses a magnetic field. When the magnet is on the haemoglobin in the blood repels the magnetic field if it still contains oxygen, and follows the direction of the magnetic field when the oxygen has been used. The scan takes images of these changes which is converted into a 3 dimensional image on a computer.
An advantage of fMRI is that is non-invasive. Unlike other scanning techniques, for example Positron Emission Tomography (PET), fMRI does not use radiation or involve inserting instruments directly into the brain, and is therefore virtually risk-free. Consequently, this should allow more patients/participants to undertake fMRI scans which could help psychologists to gather further data on the functioning human brain and therefore develop our understanding of localisation of function.
fMRI scans have good spatial resolution. Spatial resolution refers to the smallest feature (or measurement) that a scanner can detect, and is an important feature of brain scanning techniques. Greater spatial resolution allows psychologists to discriminate between different brain regions with greater accuracy.
fMRI scans do not provide a direct measure of neural activity. fMRI scans simply measure changes in blood flow and therefore it is impossible to infer causation (at a neural level). While any change in blood flow may indicate activity within a certain brain area, psychologists are unable to conclude whether this brain region is associated with a particular function.
In addition, some psychologists argue that fMRI scans can only show localisation of function within a particular area of the brain, but are limited in showing the communication that takes place among the different areas of the brain, which might be critical to neural functioning.
fMRI scans are safer than PET scans as they do not use radiation, so maybe more useful for researching human behaviour.
People with a pacemaker or metal objects in their bodies cannot have fMRI scans due to the magnetic field, so cannot be used to study all human behaviour.
fMRI scans only give an indication of brain activity, it they cannot explain other reasons for human behaviour such as imitating a role model.
It can be a distressing procedure for people who suffer from claustrophobia as they take place in a noisy confined space.
Li et al. (2013) found that activity in the PCC was associated with heroin addicts cravings, so brain scans can be used to explain addiction.
The use of quantitative data in an observation can be reductionist as it does not record the actions leading up to a behaviour so may be of limited use when studying human behaviour.
Explain one strength of Jayla using a PET scan in her research. (2) June 2017
Describe how a CAT scan is used in biological psychology. (2) October 2018
Explain two ways Jayla could have improved her study. (4) June 2017
Explain one strength and one weakness of the use of CAT scans in biological psychology. (4) October 2018
Evaluate the use of fMRI scans and the observational research method to research human behaviour. (16) October 2019