Ways of studying the brain Flashcards
Electroencephalogram (EEG)
Electrodes placed on the scalp detect small electrical charges resulting from the activity of brain cells.
Electrodes measure the activity of the cells immediately under the electrode, so using more electrodes gives a fuller picture: 2 to 100+ electrodes can be used.
Electrical signals from different electrodes are graphed over a period of time.
The four basic EEG patterns are alpha waves, beta waves, delta waves and theta waves.
Positives of using EEG’s
1)It provides a recording of the brain’s activity in real time (good temporal resolution – 1-10 milliseconds) rather than a still image of the passive brain. The researcher can therefore accurately measure a particular task with the brain activity associated with it.
2)It is useful in clinical diagnosis e.g. by recording the abnormal neural activity associated with epilepsy.
3)EEG/ERP is a cheaper method than fMRI scanning so it is more widely available to researchers.
Negatives of EGG’s
1)EEGs have poor spatial resolution (10-15mm).
Electrical activity can be picked up by several neighbouring electrodes, therefore the EEG signal is not useful for pinpointing the exact source of an activity.
It does not allow researchers to distinguish between activities originating in different but closely adjacent locations in the brain.
2)EEGs can only detect the activity in superficial regions of the brain (those close to the electrodes) and therefore cannot reveal what is going on in the deeper regions such as the hypothalamus or hippocampus.
Event-Related Potentials (ERPs)
A measure of brain activity in response to a specific stimulus (using the same equipment as EEG - electrodes placed on the scalp detect small electrical charges resulting from the activity of brain cells).
An EEG signal is time-locked to a stimulus.
The stimulus might be a word, sound or picture, for example.
ERPs are difficult to distinguish from all the other electrical activity being generated within the brain at a given time, so it usually requires a large number of trials to measure them accurately.
Strengths of ERPs
1) ERPs are a useful method to test the reliability of self-report answers, particularly when the research is potentially sensitive or open to social desirability bias. - For example, they have been used to assess whether someone is lying or telling the truth, by presenting ppts with familiar and unfamiliar stimuli and recording the difference in electrical activity. - They have also been used in addiction research to investigate the association between electrical activity in response to smoking cues and ratings of the desire and intention to smoke cigarettes.
2)An ERP can measure the processing of stimuli even in the absence of a behavioural response – useful if studying individuals with brain damage.
what did - Costa, Braun and Birbaumer (2003) do
recorded responses to nude pictures of both sexes in young people (19-29 yrs). Men said they were more aroused by the nude female pictures; women mostly reported neutral feelings to both male and female pictures. However, ERPs revealed that both sexes showed a higher response to opposite-sex nude pictures than reported by ppts. This suggests that ERPs are more accurate than self-reports.
Negatives of using ERPs
1)Because ERPs are so small and difficult to pick out from other electrical activity in the brain, it requires a large number of trials to gain meaningful data. This places limitations on the type of question that ERP readings can realistically answer.
2)Only sufficiently strong voltage changes generated across the scalp are recordable.
Important electrical activities occurring deep in the brain are not recorded, meaning that the generation of ERPs tend to be restricted to the neocortex.
Functional Magnetic Resonance Imaging (fMRI)
fMRI measures changes in brain activity while a person performs a task.
When an area of the brain becomes active, it uses more oxygen. This leads to increased blood flow, as oxygen is delivered via red blood cells.
fMRI measures changes in blood flow (as a result of oxygen consumption), indicating increased neural activity.
A magnetic field and radio signals measure the amount of energy released by haemoglobin across different areas of the brain – when it is oxygenated it reacts differently to when it is deoxygenated.
Strengths of fMRI
1)fMRI has good spatial resolution, enabling researchers to pinpoint an area of activity in the brain, to within 1-2mm.
2) Because it provides a moving picture patterns of activity can be compared, rather than just the physiology of the brain (such as in a CAT scan which provides images of the structure of an individual’s brain).
3)It is non-invasive (nothing is inserted into the brain), nor does it expose the brain to potentially harmful radiation (unlike CAT scans).
4) It offers a more objective and reliable measure of psychological processes than is possible with verbal reports.
limitations of fMRI
1)The complexity of brain activity means that interpreting an fMRI scan is a difficult task, made more challenging by the time lag between initial neural activity and the image being generated (1-4 secs) – poor temporal resolution.
2)Because fMRI measures changes in blood flow in the brain, then it is not a direct measure of neural activity in particular brain areas.
3)fMRI overlooks the networked nature of brain activity, as it focuses only on localised brain activity – it is communication amongst the different regions that is most critical to mental function.
4)fMRI machines are expensive to buy and maintain, and they require trained operators, which makes research expensive and difficult to organise.
5)The sample sizes in studies are often small due to limited availability and funding. The cost per participant is high, which makes results difficult to generalise from.
Post-Mortem Examinations
Post-mortem examinations are used to establish the underlying neurobiology of a particular behaviour.
A person’s body, including the brain, are examined after death.
Examinations can be used to see where damage had occurred in the brain and how that might explain behaviour exhibited by the individual prior to death.
One of the most famous case studies involving a post-mortem is Leborgne (“Tan”); H.M. is another example.
Strengths of Post-Mortem Examinations
1)Allows for a more detailed examination of anatomical and neurochemical aspects of the brain than would be possible with non-invasive techniques (e.g. fMRI, EEG). It enables researchers to examine deeper regions of the brain, such as the hypothalamus and hippocampus.
2)There is no discomfort experienced by the individual as they are not alive.
3)Post-mortem studies have played a central part in our understanding of localisation of function in the brain:
The case of Leborgne led to the discovery of Broca’s area (a region of the brain involved in speech production).
The case of H.M. demonstrated the importance of the hippocampus in storing new memories.
Limitations of Post-Mortem Examinations
1)The research is conducted on a dead person, so it is not possible to measure activity in the brain.
2)There are issues with comparison of functioning prior to death – there may be little information about how the individual’s brain functioned prior to their death.
It is therefore retrospective as the person is already dead.
- The researcher is unable to follow up on anything that arises from the post-mortem concerning a possible relationship between brain abnormalities and cognitive functioning.
3)Some brains may have been affected by the reason for the death i.e. disease. Also, the length of time between death and the post-mortem (neuronal changes occur during and after death), and age of death are possible confounding influences.
