Brain Scanning Flashcards
Description of a CAT scan
- Pass X-rays into the head where multiple beams are passed around the head from different angles to create a detailed structural image
CAT scan - strengths
+ useful for revealing abnormal structures such as tumours or structural damage (multiple X-ray beams used which helps surgeon plan procedure)
CAT scan - weaknesses
- Ethics & generalisability - require more radiation than traditional X-rays so cannot be used often or on pregnant women
- Limited - only provide structural information (still images) and so do not give info about activity of live brain
Description of a PET scan
- Patient injected with radioactive tracer (FDG- radioactive atom is attached to glucose)
- As the brain is working, the glucose will be used up and radioactive atoms start to break down emitting positrons
- Gamma rays produced
- High concentration = high activity = red
- Low concentration = low activity = blue
PET scan strengths
+ Show the brain in action (glucose found in high concentrations) which is useful for psychological research (e.g. Nora Volkow effect of cocaine
+ Indicates areas that are involved with experience (provide localisation)
PET scan weaknesses
- Results are not easy to interpret (difficult to draw conclusions)
- Validity - The precise location of active areas in relation to brain structure (high activity shown by red but this is a general area)
- Ethical issues - radioactive substances cause damage to tissues of the body - can kill cells or cause mutations so techniques can only be carried out every 6 months
Description of fMRI scan
- Haemodynamic responce - the areas of the brain that are most active use the most oxygen and so blood is directed there
- Head placed inside large electromagnet. Inside the magnetic field, the nuclei within the hydrogen molecules in water align themselves with the direction of the magnetic field
- Oxygen is carried to the neurons in haemoglobin within red blood cells. Haemoglobin when carrying oxygen repels a magnetic field (diamagnetic)
- Scanner detects these changes to create an image
fMRI scan - strengths
+ Show important information about which areas of the brain are active
+ Ethics - Safe method of studying the brain uses electromagnet
+ Validity - images produced are extremely clear and can show activity to the millimetre
fMRI scan - weaknesses
- Low generalisability - technique only effective is people stay completely still (difficult for children or people who are claustrophobic) & some people can’t get scans (anyone with recent metal surgical implants or cardiac pacemaker)
- Validity - 5 second time lag between brain activity and image appearing on the screen which causes problems when trying to interpret it
