Ways of studying the brain Flashcards
What are the ways of investigating the brain?
FMRI, EEG, ERPs and post-mortem examinations.
What is fMRI?
MRI works by detecting the changes in blood oxygenation and flow that occur as a result of neural (brain) activity in specific parts of the brain. When a brain area is more active it consumes more oxygen and to meet this increased demand, blood flow is directed to the active area (known as the haemodynamic response).
MRI produces 3-dimensional images (activation maps) showing which parts of the brain are involved in a particular mental process and this has important implications for our understanding of localisation of function.
What are the strengths of fMRI?
Unlike other scanning techniques such as PET, it does not rely on the use of radiation.
If administered correctly it is virtually risk-free, non-invasive and straightforward to use.
It also produces images that have very high spatial resolution, depicting detail by the millimetre, and providing a clear picture of how brain activity is localised.
What are the limitations of fMRI?
fMRI is expensive compared to other neuroimaging techniques.
Can only capture a clear image if the person stays perfectly still.
It has poor temporal resolution because there is around a 5-second time-lag behind the image on screen and the initial firing of neuronal activity.
fMRI can only measure blood flow in the brain, it cannot home in on the activity of individual neurons and so it can be difficult to tell exactly what kind of brain activity is being represented on screen.
What is an EEG?
EEGs measure electrical activity within the brain via electrodes that are fixed to an individual’s scalp using a skull cap. The scan recording represents the brainwave patterns that are generated from the action of millions of neurons, providing an overall account of brain activity. EEG is often used by clinicians as a diagnostic tool as unusual arrhythmic patterns of activity (i.e. no particular rhythm) may indicate neurological abnormalities such as epilepsy, tumours or disorders of sleep.
What are the strengths of EEG?
It has contributed much to our understanding of the stages involved in sleep.
Provided invaluable in the diagnosis of conditions such as epilepsy, a disorder characterised by random bursts of activity in the brain that can easily be detected on screen.
Unlike fMRI, EEG technology has extremely high temporal resolution - EEG technology can accurately detect brain activity at a resolution of a single millisecond (and even less in some cases)
What is a limitation of EEG?
EEG signal is not useful for pinpointing the exact source of neural activity, and it does not allow researchers to distinguish between activities originating in different but adjacent locations allow researchers to distinguish between activities originating in different but adjacent locations
What is ERPs?
Although EEG has many scientific and clinical applications, in its raw form it is a crude and overly general measure of brain activity. However, within EEG data are contained all the neural responses associated with specific sensory, cognitive and motor events that may be of interest to cognitive neuroscientists. As such, researchers have developed a way of teasing out and isolating these responses.
Using a statistical averaging technique, all extraneous brain activity from the original EEG recording is filtered out leaving only those responses that relate to, say, the presentation of a specific stimulus or performance of a specific task. What remains are event-related potentials: types of brainwaves that are triggered by particular events. Research has revealed many different forms of ERP and how, for example, these are linked to cognitive processes such as attention and perception.
What are the strengths of ERPs?
These bring much more specificity to the measurement of neural processes than could ever be achieved using raw EEG data.
As ERPs are derived from EEG measurements, they have excellent temporal resolution, especially when compared to neuroimaging techniques such as fMRI, and this has led to their widespread use in the measurement of cognitive functions and deficits.
Researchers have been able to identify many different types of ERP and describe the precise role of these in cognitive functioning; for instance, the P300 component is thought to be involved in the allocation of attentional resources and the maintenance of working memory.
What are the limitations of ERPs?
A lack of standardisation in ERP methodology between different research studies which makes it difficult to confirm findings.
In order to establish pure data in ERP studies, background noise and extraneous material must be eliminated, and this may not always be easy to achieve.
What are post-mortem examinations?
A technique involving the analysis of a person’s brain following their death. In psychological research, individuals whose brains are subject to a post-mortem are likely to be those who have a rare disorder and have experienced unusual deficits in mental processes or behaviour during their lifetime. Areas of damage within the brain are examined after death as a means of establishing the likely cause of the affliction the person experienced. This may also involve comparison with a neurotypical brain in order to ascertain the extent of the difference.
What are the strengths of post-mortem examinations?
Post-mortem evidence was vital in providing a foundation for early understanding of key processes in the brain. Paul Broca and Karl Wernicke both relied on post-mortem studies in establishing links between language, brain and behaviour decades before neuroimaging ever became a possibility.
Post-mortem studies improve medical knowledge and help generate hypotheses for further study.
What are the limitations of post-mortem examinations?
Causation is an issue within these investigations.
Observed damage to the brain may not be linked to the deficits under review but to some other unrelated trauma or decay.
Post-mortem studies raise ethical issues of consent from the patient before death. Patients may not be able to provide informed consent, for example in the case of HM who lost his ability to form memories and was not able to provide such consent - nevertheless post-mortem research has been conducted on his brain.
