STUDYING THE BRAIN; Functional Magnetic Resonance Imaging (fMRI)
1. Functional Magnetic Resonance Imaging (fMRI)
Functional magnetic resonance imaging (fMRI) is a brain-scanning technique that measures blood flow(혈류) in the brain when a person performs a task. fMRI works on the premise(전제) that neurons in the brain that are the most active during a task use the most energy. Energy requires glucose and oxygen(포도당;글루코스와 산소). Oxygen is carried in the bloodstream(혈류) attached to haemoglobin (found in red blood cells) and is released for use by these active neurons, at which point the haemoglobin becomes deoxygenated(to remove oxygen from a substance). Deoxygenated haemoglobin has a different magnetic((of a metal object or material) able to attract objects or materials containing iron or steel) quality from oxygenated haemoglobin. An fMRI can detect these different magnetic qualities and can be used to create a dynamic (moving) 3D map of the brain, highlighting which areas are involved in different neural activities. fMRI images show activity approximately 1-4 seconds after it occurs and are thought to be accurate within 1-2 mm. An increase in blood flow is a response to the need for more oxygen in that area of the brain when it becomes active, suggesting an increase in neural activity.
Evaluation of fMRI
● Invasive or Non-Invasive: An advantage of fMRI is that is non-invasive. Unlike other scanning techniques, for example Positron Emission Tomography (PET), fMRI does not use radiation(a form of energy that comes from a nuclear reaction and that can be very dangerous to health) or involve inserting instruments directly into the brain, and is therefore virtually(almost) risk-free. Consequently, this should allow more patients/participants to undertake(to do or begin to do something, especially something that will take a long time or be difficult) fMRI scans which could help psychologists to gather further data on the functioning human brain and therefore develop our understanding of localisation(Alternative spelling of localization) of function.
● Spatial Resolution: fMRI scans have good spatial(relating to the position, area, and size of things) resolution(the ability of a microscope, or a television or computer screen, to show things clearly and with a lot of detail). Spatial resolution refers to the smallest feature (or measurement) that a scanner can detect, and is an important feature of brain scanning techniques. Greater spatial resolution allows psychologists to discriminate between different brain regions with greater accuracy. fMRI scans have a spatial resolution of approximately 1-2 mm which is significantly greater than the other techniques (EEG, ERP, etc.) Consequently, psychologists can determine the activity of different brain regions with greater accuracy when using fMRI, in comparison to when using EEG and/or ERP.
● Temporal Resolution: fMRI scans have poor temporal(relating to time) resolution. Temporal resolution refers to the accuracy of the scanner in relation of time: or how quickly the scanner can detect changes in brain activity. fMRI scans have a temporal resolution of 1-4 seconds which is worse than other techniques (e.g. EEG/ERP which have a temporal resolution of 1-10 milliseconds). Consequently, psychologists are unable to predict with a high degree of accuracy the onset(the beginning of something) of brain activity.
● Causation(the process of causing something to happen or exist): fMRI scans do not provide a direct measure of neural activity. fMRI scans simply measure changes in blood flow and therefore it is impossible to infer causation (at a neural level). While any change in blood flow may indicate activity within a certain brain area, psychologists are unable to conclude whether this brain region is associated with a particular function.
▷ In addition, some psychologists argue that fMRI scans can only show localisation of function within a particular area of the brain, but are limited in showing the communication that takes place(to happen) among the different areas of the brain, which might be critical to neural functioning