Brain scans

• PET scan strength:

  • Shows the brain in action which is very useful for psychological research linking biological activity to behaviour
• PET scan strength:

  • Indicate specific areas of the brain are involved in experience, i.e. is useful for localisation of function
• PET scan weakness:

  • Injecting the radioactive tracer is an invasive procedure and radiation can be harmful so there are ethical implications
• PET scan weakness:

  • It is difficult to isolate different brain functions specifically so we can’t be certain which part of the brain is performing which function (low validity)
• fMRI strength:

  • There is no danger from radiation, and it is non-invasive, so it is the main type of scan chosen to use since the 1990’
• fMRI strength:

  • Detection of changes in blood flow is very precise so the scanning technique is very accurate which is excellent when used in medicine (or research)
• fMRI weakness :

  • Is unable to look at receptors of neurotransmitters, whereas a PET scan can do this, so it is not suitable for everything
• fMRI weakness:

  • If the patient moves it can distort the image and there is a time lag between the brain activity and the image appearing, which can cause problems when interpreting the scan
• CAT scan strength:

  • Valuable in medicine to detect changes in physical structures to diagnose patients (i.e. good application)
• CAT scan strength:

  • Is not painful and is non-invasive
• CAT scan weakness:

  • X-rays can cause damage e.g. cancers as patients are exposed to a years-worth of radiation so they are used sparingly
• CAT scan weakness:

  • Limited use in research as still images only provide structural information
• CAT scan Uses x-rays and a computer to create detailed  structural images of the inside of the body, including the brain
• In a CAT scan The person lies inside a large doughnut shaped scanner and the scanner is slowly rotated around them.
• In an CAT scan Images of the brain or body are taken from different angles. Each image is a cross-section of the person’s brain or body.
• When all the ‘slices’ of the CAT scan are put together this can build up a very detailed picture. Sometimes a dye is used to make the picture clearer, such as barium or iodine.
• The CAT scan takes from a few minutes to 30 minutes.
• in a CAT scan Pictures show how the area being scanned reacts to the x-ray, showing how far the x-ray is blocked, which could indicate a tumour or brain damage. 
• full A01 for CAT scan:

  Uses x-rays and computer to create detailed structural images of inside of body/brain. The person lies inside doughnut shaped scanner and the scanner is rotated around them. Images of the brain/body are taken from different angles. Each image is a cross-section of the person’s brain/body. the ‘slices’ are put together to build up a detailed picture. scan takes from a few minutes to 30 minutes. Pictures show how the area being scanned reacts to the x-ray, showing how far the x-ray is blocked, which could indicate a tumour/brain damage. 
• PET scan Measures metabolic activity in the brain through blood flow. Injected with a small amount of radioactive substance though a vein in the arm. Brain areas which are most active will use more of it and so be detected by the scanner.
• The info on the brain is sent to a computer. Most active areas are coloured red or yellow and the least are represented as blue. It allows researchers to work out what parts of the brain are working at what time. The tracer contains small positively charged particles called positrons. It can be used to measure blood flow in the brain. PET can be used to map different types of neurotransmitter receptor in the brain.
• fMRI  (Functional Magnetic Resonance Imaging) uses radio waves to measure blood oxygen levels in the brain.
• When a certain area of the brain is active, it pulls oxygenated blood to that area which is associated with increases in neuronal activity (haemodynamic response).  Deoxygenated blood has magnetic properties (because oxygen neutralizes the effect of iron in the blood). So the ratio of oxygenated blood to deoxygenated blood can be picked up as a signal by the magnetic field of fMRI which produce a series of images of successive slices which are converted into a 3D image by a computer. fMRI has a very high spatial resolution, so the images it produces are very detailed
• CAT scans require more radiation than traditional X-rays, and the more detailed and complex the CAT scan is the more radiation exposure the patient receives. This means that CAT scans cannot be used  very often as receiving large amounts of radiation is harmful for the human body
• CAT scans only provide structural information about bone, soft tissue and blood vessels but, unlike other scans, such as PET scans, it does not give information about activity of the ‘live’ brain, they just produce still images.
• This means CAT scans have a limited use in psychological research linking the function of brain areas to particular behaviours compared to PET and fMRI, both of which record brain activity, as they cannot be used to determine the effect of activities on the brain in live tasks, they can only to see the physical structures.
• Therefore, CAT scans are useful for identifying areas of brain damage which could relate to behaviour such as aggression, but cannot be used to clarify the function of brain areas in active tasks so may be less useful in understanding the causes of aggression, which happen in everyday situations
• This is a strength because PET scans can indicate which specific areas of the brain are actively involved in behaviour, i.e. is useful for establishing which areas are localised for which functions. PET scans are useful because it can help researchers understand which parts of the brain are responsible for which functions in the brain.  It’s also useful because we can look at neurotransmitter receptors in the brain which other scans cannot detect.
• The PET scan could be weaker due to the fact that it requires interpretations which could cause bias in the results of the scans

  Injecting the radioactive tracer is an invasive procedure and radiation can be harmful so there are ethical implications. It is difficult to isolate different brain functions specifically so we can’t be certain which part of the brain is performing which function (low validity)
• Uses radio waves to measure oxygen levels in the brain. It measures blood flow in the brain when a patient 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. Head phones are used, as the scan causes a very loud banging sound and the person lies down lie on a moving platform and must stay very still while they are moved into the machine, which can feel claustrophobic and it takes a long time for the scan to be completed, up to 30 mins.
• In a PET scan Person injected with small amounts of radioactive substance into a vein in the arm e.g. glucose, the radioactive-tracer.  The person must lie still on a moving platform to be passed through the scanner.
• The procedure of CAT scanning is for someone to lie on a moving platform to be passed through the scanner or for the person to lie still and for the scanner to move around them. Multiple beams are passed to the head by X- ray.
• FMRI

  • Produces an image of the brain without using radiation
  • A brain is scanned using a very powerful electromagnet 
  • When neural activity increases in the brain, blood flow increases in active areas to keep up the demand for oxygen. 
  • The oxygen is carried to neurons in the haemoglobin within red blood cells. 
  • Haemoglobin, when carrying oxygen repels the magnetic field but when it has been deoxygenated it follows the direction of the magnetic field.
  • The scanner sends the information to the computer to create a map to show changing levels of neural activity.
• PET

  • uses radiation
  • Higher amount of gamma rays the higher amount of brain activity in a particular area of the brain
  • A radioactive atom is attracted to the glucose because the brain will use up the glucose as a from of energy
  • Warm colours indicate high activity, cold colours indicate low activity 
  • As brain is working the glucose is used up and radioactive atones start to break down emitting positrons 
  • Inject the patient with a small amount of radioactive
  • material called fluorodeoxyglucose (FDG)
  • Once the tracer is absorbed by the bloodstream a task may be given to stimulate the brain.
• CAT

  • uses radiation
  • Multiple beams are passed around the head from different angles
  • Pass an X-ray into the head
  • A computer interprets the x ray beams
  • They create slices of sections of the area being investigated producing a drawing of the slices. The slices can put together to form a three dimensional image
  • Useful in detecting areas of brain damage or position of brain tumour