research methods: brain scanning techniques

Question 1

what does pet scan stand for?

Answer 1

• positron emission tomography

Question 2

what does a pet scan do?

Answer 2

• measures metabolic activity in the brain e.g. the areas that are most active
• person is injected with small amount of radioactive substance such as fleurodeoxyglucose (the radiotracer).
• brain areas which are most active will use more of it and this can be detected by scanner
• information is sent to a computer
• most active areas are coloured red or yellow
• least active areas are represented as blue

Question 3

strengths of pet scans: ethics

Answer 3

• reasonably non-invasive way of studying inside the brain (and body). individual has to have the radioactive tracer injected, which is invasive, but the images are taken from outside the body, which is less dangerous and less distressing than surgery. surgery for research purposes is carried out using animals, so scans using humans are more ethical for that reason. pet scanning is therefore a reasonable non-invasive and ethical way of researching the brain.

Question 4

strengths of pet scans: validity

Answer 4

• with all scanning techniques, there is validity - scan can measure what it claims to measure. it is not easy to check validity when it comes to cognitive functions, such as using language. however, when speech is studied using pet scans it was confirmed what was previously thought to be the area for speech (found by examining the brains of people who had speech problems when they died) was indeed the area of activity. scanning seems to be a valid measure

Question 5

strengths of pet scans: reliability

Answer 5

• pet scanning can be reliable because it can be repeated and same results found again. this can be tested, e.g. when someone speaks, the same area of the brain is used. the same areas of the brain are consistently found for different activities, which means the method is reliable

Question 6

weaknesses of pet scans: ethics

Answer 6

• use of radioactive tracer is invasive procedure and so there are ethical implications for individual. researcher must follow ethical guidelines carefully. injecting someone with a substance is not something to be done lightly. there are to be informed consent and a good reason for carrying it out. scan itself can make some people panic because of having one’s head inside a tube can be claustrophobic experience and this must be fully explained to ppt

Question 7

weaknesses of pet scans: validity

Answer 7

• although activity shows up quite clearly on the image, it is difficult to isolate different brain functioning precisely. e.g. people can read passages of test while being scanned, but they would almost certainly be using other parts of their brain as well. pet scans are valid to a point, it is hard to claim from a scan exactly what part of the brain is performing which function, and this is often the aim of the research. consequently the validity of any findings can be criticised

Question 8

what does cat scan stand for?

Answer 8

• computerised axial/assisted tomography scan

Question 9

what does a cat scan do?

Answer 9

• uses x-ray beams and a computer to create detailed structural images of the inside of the body, including the brain
• patient is injected with iodine into back of hand or into crook of elbow before having cat scan which flows around blood stream to highlight blood vessels in brain, which helps create clear image for analysis
• person lies inside large doughnut-shaped scanner and scanner is slowly rotated around the,.
• images of brain are taken from different angles
• each image is a cross-section of person’s brain.
• when all the slices are put together, this can build up a very detailed picture

Question 10

strength and ca of cat scans: ethics

Answer 10

• cat scanning is less harmful than pet scans, which use radioactive tracer, although x-rays can be damaging so are used infrequently

Question 11

strength of cat scans: application

Answer 11

• cat scan can changes in physical structures to quite a good level and so it is valuable when looking for tumours or haemorrhages, particularly as it produces a 3d image, which helps diagnoses (used in medicine not psychology). can also be used in industry, therefore meaning it has wide application, including studying damage to brain of individuals to help with study of brain

Question 12

weakness of cat scans: application

Answer 12

• mri gives a clearer picture when it comes to examining causes of headache for example and is more likely to be used when scanning the brain, as it fits more with the need in psychology

Question 13

strength of cat scans: ethics

Answer 13

• a cat scan is not painful at all and is non-invasive, which means there is no need to ‘enter’ the body, although if a dye is used, that is not entirely the case

Question 14

weakness of cat scans: ethics

Answer 14

• involves x-raying, which can cause damage, notably cancers. a known feature of this type of scanning, so they are used sparingly. this means as a method of studying the brain for research purposes, it would not be a suggested method. the radiation someone is normally exposed to in a year is experienced is one cat scan

Question 15

what does fmri scanning stand for?

Answer 15

• functional magnetic resonance imaging

Question 16

what does a fmri scan do?

Answer 16

• uses radio waves to measure blood oxygen levels in the brain
• those areas of the brain that are most active use most oxygen and therefore blood is directed to the active area. this is a haemodynamic response
• patients are injected with a dye called contrast medium, which helps to show up relevant area in the brain
• may be placed in a brace to help you stay still, also get give a mask that is created especially for you. may be given special goggles and earphones so that audio-visual stimuli (e.g. projection from a computer screen or recorded sounds) may be administered during the scan
• this activity/response is picked up through radio signals and these signals produce a series of images of successive slices, which are then turned into a 3d image by a computer

Question 17

weakness of fmri scans: validity

Answer 17

• cannot look at the actual receptors of neurotransmitters, whereas pet scans can, so fmri scans are not suitable for everything that a pet scan can do

Question 18

strength of fmri scans: ethics

Answer 18

• there is no danger from radiation, unlike cat scanning and to an extent pet scanning. from the 1990s, fmri has been the main type of scan chosen because there is no invasion or surgery and no radiation exposure

Question 19

weakness of fmri scans: validity

Answer 19

• there can be problems with using fmri scanning - too much head movement can distort the imaging
• if an fmri is used to see where certain types of information processing takes place in the brain, and the idea is to measure the brain at rest and then the brain when using that functioning, there is an issue in that the brain is never at rest. it is not easy to gather a baseline measure. e.g. even breathing is an activity that requires processing in the brain

Question 20

weakness of fmri scans: ethics

Answer 20

• there are risks when undergoing fmri scans, such as those who have pacemakers and more generally because of issues such as claustrophobia. scanning is not risk free. e.g. there can be tingling felt when magnetic fields switch around scans

Question 21

strengths of fmri scans: validity and application

Answer 21

• detection of blood flow is very precise so even slight changes can be detected. this means that for medical use, fmri is very good at detecting issues around strokes. also, sensitivity to blood flow changes makes fmri very good for looking at brain structure and functioning when it comes to learning about the brain. cognitive tasks can be carried out and the brain areas in use are identified clearly

Question 22

evidence for pet scanning

Answer 22

• Raine et al. 1997 used pet scanning technique to investigate whether people charged with murder and pleading not guilty by reason of insanity, to see if there were brain differences that might link to their aggressions
• this scanning technique was used to look for differences in brain functioning between murderers who pleaded not guilty by reason of insanity and control group

Question 23

evidence for cat scans

Answer 23

• Betts 2009 cites case of Herbert Weinstein, 64 year old man who strangled his wife in 1991 after argument
• his defence was that a cyst had caused pressure on his pre-frontal cortex which had affected his understanding of right and wrong
• there was cat scan evidence of differences in his brain (widening sulci) that related to those with schizophrenia
• after long debated argument, evidence was admitted, and he was acquitted but admitted to a hospital
• a lot of similar evidence of the use of neuroimaging in trials, some related to amygdala and aggression

Question 24

evidence for fmri scans

Answer 24

• Dimoka 2010 used fmri neuroimaging to look at trust and distrust, the idea was to use neuroimaging to see if evidence of brain function and structure linked to trust and distrust would complement evidence from psychometric testing
• found that credibility and discredibility (how far you think someone is credible) linked to the cognitive brain areas of the prefrontal cortex
• benevolence and malevolence (whether you think someone is kind or not) linked to emotion area of brain (limbic system)