Brain Imaging Technology - BLOA
What information can fMRI provides?
fMRI images brain function and the far superior temporal resolution of fMRI relative to PET.
How fMRI works?
fMRI obtains a 'functional' image of the brain by measuring blood oxygenation. When an area is more active, it uses more oxygen.
What are the three types of brain imaging technology we have learnt?
1. PET (positron emission tomography) scan 2. MRI (Magnetic Resonance Imaging) 3. fMRI (functional MRI)
Provide one or more studies to support the answer above.
A longitudinal study (Masconi 2005) they followed a sample of 53 normal and health participants for between 9 and 24 years. They found that individuals that who showed early signs of reduced metabolism in the hippocampus were associated with later development of Alzheimer's disease. The hippocampus, a region of the brain that is active in learning and short-term memory is affected in the early stages of Alzheimer's and it is believed that through a PET scan of hippocampus that it will be possible to see the first signs of Alzheimer's disease long before it has spread to the cerebral cortex, which damages cognitive function and impairs the memory. The results still need to be replicated, but this could be beneficial in early detection and treatment in patients that are yet to develop symptoms.
How PET scan works?
By injecting a small amount of a radioactive material, Fluorodeoxyglucose (FDG) into the patient's veins. The substance travels through the bloodstream and collects in organs and tissues and after a waiting period, which allows the substance to collect in the tissues of interest, the subject is placed on the imaging scanner. They serve as markers of blood flow or metabolic activity in the brain, which can provide a colour-coded map indicating which areas of the brain become active when participants do a number of activities. Red means the most active, followed by orange and yellow while green, blue or black means inactive.
What information can PET scan provides?
It provides a three-dimensional image of functional processes in the body. That is, PET scans can examine brain function, mapping actual activity in the brain over time.
What information can MRI provides?
MRI provides a three dimensional picture of brain structures. It is especially useful for detecting small anatomical changes as a result of disease processes or trauma in the brain.
How MRI be used to investigate the relationship between biological factors and human behaviour?
Maquire et al's London Taxi driver study made use of MRI technology. Maguire et al. were attempting to demonstrate the plasticity of the brain. Maguire et al. set out to discover whether morphologica changes could be detected in the healthy human brain associated with extensive experience of spatial navigation. Their prediction was that the hippocampus would be the most likely brain region to show changes. To test this prediction the researchers decided to study London taxi drivers because they rely heavily on spatial navigation skills in their working lives. London taxi drivers have to undertake extensive training known as "The Knowledge" and during this time they have to acquire a vast spatial memory of the roads of central London. The participants for this study were 16 healthy, right-handed male licensed London taxi drivers. The taxi drivers were compared with the structural MRI scans of 50 healthy right-handed males who did not drive taxis. The scans of the 50 control participants were selected from the structural MRI scan database at the same unit where the taxi drivers were scanned. The first main findings of the research were that the posterior hippocampi of taxi drivers were significantly larger relative to those of control subjects.
How PET scan be used to investigate the relationship between biological factors and human behaviour?
PET scan might be a method to detect Alzheimer's disease in the very early stage when memory and cognitive impairment are not noticeable yet. Alzheimer's disease is a kind of dementia and symptoms of Alzheimer's disease could be memory loss, confusion, language problems, and sometimes incapacity to form new memories. As Alzheimer's disease is a progressive and irreversible neurological disorder, which attacks brain cells and causes many behavioural changes, early detection is essential to enhance a quality life for the patient as there has no cure for Alzheimer's disease but only medication to slow it down.
How MRI works?
The MRI scanner worked by exposing a participant's brain to a strong magnetic field and radio waves to produce detailed pictures of the brain. Computer software then converted the information into a 3D image of the brain.
Limitations of the use of these imaging techniques.
The fMRI and PET scanner are not natural environments for behaviour; therefore, there is a question of ecological validity. However, although the task of being scanned in an MRI or PET scanner is hardly ecologically valid it would not be possible for the participants to respond to demand characteristics. Furthermore, research of this kind cannot establish a cause effect relationship. No variable was manipulated by the researchers and there was no random allocation to groups. Researchers still usually have to make inferences from any scans obtained. Brain areas activate for different reasons. We do not know for example that the changes seen in the brains of the London's taxi drivers are not the result of stress, rather than as a result of memory. Some researchers have suggested that the use of colours may exaggerate the different activities of the brain. Brain imaging technologies such as these are of course costly techniques in terms of expensive equipment and researchers' time, although the use of computers does make very sophisticated analysis possible. PET scans in particular are very expensive. The fMRI and MRI are non invasive although some people can feel uncomfortable in the tight spaces. Although PET scan is harmless, it does use small amounts of radiation which makes it slightly invasive.
Benefits of the use of these imaging techniques.
These scanning technologies do not pose any health risks to the participants and thus participants in research using these types of technology should not be negatively affected by their experience. PET scans are useful in early diagnosis of Alzheimer's disease and they provide useful images of metabolic activity and structure in the brain. Both the fMRI and the MRI show actual brain activity and indicate when certain areas of the brain are active when engaged in behaviours. FMRI have higher resolutions than PET scans and are easier to carry out. In short each of these imaging techniques provide valuable insights into the relationship between biological factors and human behavior.
How fMRI be used to investigate the relationship between biological factors and human behaviour?
This is used to see what areas are active when people perform cognitive tasks such as reading or problem solving.
Use one or more studies to support the answer above.
fMRI was used in a similar associated study in order to determine which areas of the brain were active when the London Taxi drivers went through the process of mentally navigating their way through a virtual simulation of London's streets. Different brain regions were activated as they considered route options, spotted familiar landmarks or thought about their customers. The scientists used fMRI to obtain "minute by minute" brain images from 20 taxi drivers as they delivered customers to destinations on "virtual jobs". The scientists adapted the Playstation2 game "Getaway" to bring the streets of London into the scanner. After the scan the drivers watched a replay of their performance and reported what they had been thinking at each stage. The hippocampus was only active when the taxi drivers initially planned their route, or if they had to completely change their destination during the course of the journey. The scientists saw activity in a different brain region when the drivers came across an unexpected situation - for example, a blocked-off junction.