5. ways of investigating the brain Flashcards
The purpose of scanning in psychological research is often to
investigate localisation - to determine which parts of the brain do what.
Functional magnetic resonance imaging (fMRI) works by detecting the changes in both blood oxygenation and flow that occur as a result of neural 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.. fMRI produces three- dimensional images showing which parts of the brain are involved in a particular mental process - this has important implications for our understanding of localisation of function.
An electroencephalogram (EEG) measures
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 thousands of neurons, providing an overall account of brain activity.
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 (ERPs) - 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.
POST-MORTEM EXAMINATION
is 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 examination are likely to be those who
have a rare disorder and have experienced unusual deficits in cognitive 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.
AO3: strengths of fMRI
risk free, high resolution
One key strength of fMRI is, 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.
This means that fMRI can safely provide a clear picture of brain activity.
AO3: limitation of fMRI
fMRI is expensive compared to other neuroimaging techniques.
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.
This means MRI may not truly represent moment-to-moment brain activity.
AO3: strength of EEG
practical application
EEG has been useful in studying the stages of sleep and 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.
This shows the real-world usefulness of the technique.
AO3: limitation of EEG
does not allow researchers to distinguish between activities
The main drawback of EEG lies in the generalised nature of the information received (that of many thousands of neurons).
The EEG signal is also not useful for pinpointing the exact source of neural activity.
Therefore, it does not allow researchers to distinguish between activities originating in different but adjacent locations.
AO3: strength of ERP
The limitations of EEG are partly addressed through the use of ERPs which 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. This means that ERPs are frequently used to measure cognitive functions and deficits such as the allocation of attentional resources and the maintenance of working memory.
AO3: limitations of ERP
lack of standardiation, unpure data
Critics have pointed to a lack of standardisation in ERP methodology between different research studies which makes it difficult to confirm findings.
A further issue is that, in order to establish pure data in ERP studies, background ‘noise’ and extraneous material must be completely eliminated.
This is a problem because it may not always be easy to achieve.
AO3: strength of post mortems
real life application - useful
Post-mortem evidence was vital in providing a foundation for early understanding of key processes in the brain. Broca and 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 were also used to study HM’s brain to identify the areas of damage, which could then be associated with his memory deficits.
This means post-mortems continue to provide useful information.
AO3: limitation of post mortems
causation, lack of consent
Causation is an issue within these studies observed damage to the brain may not be linked to the deficits under review but to some other unrelated trauma or decay.
A further problem is that post-mortem studies raise ethical issues of consent from the individual before death participants 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, but post-mortem research has been conducted on his brain.
This challenges the usefulness of post-mortem studies in psychological research.
