Using Scanning to Study the Brain Flashcards
Why do we use brain scans?
Helps understand the relationship between different parts of the brain and their functions; helps locate affected areas in the brain by neurological disorders and devise new strategies of scanning for treatment
How is the procedure similar for all types of scans?
The individual lies down in the scanner, as still as possible, whilst detectors circle their heads, obtaining information about one ‘thin slice’ of brain at a time
How is ‘thin slices’ produced by brain scans useful?
Using multiple “slices”, we can build up a 3D image of the brain
define spatial resolution
how much fine detail is presented in the scan image
Why is spatial resolution good?
high spatial resolution shows more detailed images
define temporal resolution
how well the scanner tracks the changes in brain activity over time
why is temporal resolution good?
higher temporal resolution scanners are more responsive to short-term changes in the brain
Define voxel size
a 3D pixel, on the image of a scan
What is C.A.T stand for?
Computerised Axial Tomography
How are CAT scans similar to X-rays?
It involves passing x-rays though a person’s brain where the beams are then interpreted by a computer however, unlike an X-ray, it uses multiple angles of the brain
Why are CAT scans considered useful?
they are useful for detecting damage or tumours as well as allowing a detailed picture of the brain to be seen
What do CAT images show?
a grey-scale image, of high detail about the structure of the brain: images of bone, soft tissue and blood vessels imaged simultaneously
How are CAT scans inferior to PET/fMRI scans?
they do not convey information about brain activity or function which limits their psychological usefulness
how are CAT scan useful in terms of psychologically understanding?
Their level of detail in brain structures is useful when relating brain damage to psychological functioning
What are CAT scan’s resolutions?
Spatial resolution of 0.5mm (voxel size) and no temporal resolution as it only creates images of brain structure
How much does a CAT scan cost?
Around £1 million and takes round 5 minutes per scan, which roughly translates to £100-£400 per scan
What are the strengths of CAT scans?
Easier to plan surgeries as structures are seen before beginning the operation
Non-invasive, though sometimes a dye is injected for higher clarity
Removes the need for exploratory surgery
Reduces the time an individual must spend under general anaesthetic
Cheaper and somewhat faster than PET/fMRI scans
What are the weaknesses of CAT scans?
- Involves radiation, and therefore unadvised for pregnant women as radiation may harm the unborn child
- Risk of overexposure to radiation,
What does f.M.R.I stand for?
Functional Magnetic Resonance Imaging
How does an fMRI scan work?
It scans the blood flow in the brain. The individual’s head is placed within a large electromagnet, and they are given a task to do. As neural activity increases, so does blood flow: active areas require more blood and the scan shows where the blood goes. The haemoglobin within the blood dispels the magnetic field when oxygenated and goes with the magnetic field when deoxygenated - these differences help the scanner to create an image.
Why is fMRI scans favoured by scientists more so than PET scans?
It has a higher spatial resolution, non-invasive and lacks radiation exposure to the participant
Why is fMRI scan practically useful?
No need for radioactive tracers, although small movements may badly affect fMRI scans and so cannot be used to may different types of chemicals within the brain like PET scans`
How are fMRI scans similar to PET scans?
They both generate images of active brain areas, and so have the same applications and strengths
What is the resolution of fMRI scans?
1.5mm (voxel size) spatial resolution and a temporal resolution of 20 seconds
How much does a fMRI scan cost?
A scanner cost around £1.9 million, and takes around 30-40 seconds which roughly translates to around £200- £500 per scan
What are the strengths of fMRI scans?
- High temporal resolution (with 4 images per second)
- Can be done during tasks, allowing scientists to infer about brain localisation and function
-Non invasive
What are the weaknesses of fMRI scans?
- Can trigger claustrophobia for some patients as they would have to lie still in a large tube for the duration of the scan
- Unsuitable for some magnets or people with pacemakers/recent metallic surgical implants
What does P.E.T scan stand for?
Positron Emission Tomography
How do PET scans work?
A patient is injected with radioactive substances (FDG) which conducts the scan. Once the radioactive tracer is absorbed into the bloodstream (which takes around 30 mins), a task is given to stimulate the blood supply within the brain and encourage activity. The tracer attaches itself onto glucose molecules (which are used as energy by the brain). Once the glucose is used up, the tracers produce gamma rays which are picked up by the scammer: a high activity within a brain region means a higher concentration of gamma rays within that region (warm colours).
How are PET scans useful to scientists and psychologists?
Its ability to investigate brain activity makes it useful, as brain activity can be compared to different tasks to strengthen localisation of the brain - it can investigate a wider range of brain functions and behaviours, through mapping different types of chemicals within the brain
What are the limitations of PET scans in relation to fMRI and CAT scans?
Brain structure portrayal is less detailed
What are the resolution within PET scans?
Spatial resolution of 6mm (voxel size) and a temporal resolution of 5-15 mins
How much does a PET scan cost?
A scanner costs around £2 -3 million, with higher running costs due to the need to have a facility to make the short-lived radioactive isotopes used as radioactive tracers and hence this roughly translates to £500-£800
What are the strengths of PET scans?
- Helps doctors see existing problems and predict future problems
- Good for monitoring of progressive neurodegenerative diseases
What are the negatives of PET scans?
- Cannot have too many scans as this will negatively affect the patient’s health
- More invasive than CAT scans, and some may object to the insertion of radioactive tracers (although it does decay quickly)
-Expensive and hence only used for diagnostic purposes
Why is Raine et al. (1997) important when using scanning to understand the brain?
Raine et al. (1997) used PET scans to compare murderers with ordinary people. They found that the murderers had different patterns of brain activity in the forebrain and the limbic system.
Why is Hirvonen et al. (2011) important when using scanning to understand the brain?
Hirvonen et al. (2011) used PET scans to show that long-term users of cannabinoid drugs show changes to the brain.
Why is Gazer et al. (2000) important when using scanning to understand the brain?
Gazer et al. (2000) used MRI scans to show that schizophrenia patients had reduced volumes of brain tissue compared to a comparison group.
Why is Carlsson et al. (2000) important when using scanning to understand the brain?
Carlsson et al. (2000) used a range of studies, including brain imaging to show that schizophrenia is related to abnormalities in brain systems that use dopamine and glutamate as their main neurotransmitter.
Define brain scanning/imaging
using technology to produce images of brain structure and/or activity without needing to open up the skull.
Define CAT scan
an imaging technology that uses X-rays to generate pictures of brain structure.
Define PET scan
an imaging technology that generates images of brain activity by tracing the uptake of glucose in different brain areas.
Define fMRI scan
an imaging technology that generates images of brain structure and activity by tracking the movement of water/blood in different brain areas.
What research methods are used when trying to understand how brain scanning is used to understand the brain?
Brain-scanning techniques (CAT, PET and fMRI)
