Brain Scanning

Question 1

Description of a CAT scan

Answer 1

• Pass X-rays into the head where multiple beams are passed around the head from different angles to create a detailed structural image

Question 2

CAT scan - strengths

Answer 2

+ useful for revealing abnormal structures such as tumours or structural damage (multiple X-ray beams used which helps surgeon plan procedure)

Question 3

CAT scan - weaknesses

Answer 3

• 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

Question 4

Description of a PET scan

Answer 4

• 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

Question 5

PET scan strengths

Answer 5

+ 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)

Question 6

PET scan weaknesses

Answer 6

• 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

Question 7

Description of fMRI scan

Answer 7

• 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

Question 8

fMRI scan - strengths

Answer 8

+ 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

Question 9

fMRI scan - weaknesses

Answer 9

• 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