ways of investigating the brain

fMRI - knowledge

• works by detecting the changes in blood oxygenation and flow that occur as a result of neural activity in specific parts of the brain.

• oxygen is carried to the brain by haemoglobin in red blood cells, and when a specific area of the brain becomes more active, it consumes more oxygen so more haemoglobin is present, and to meet this increased demand, the blood flow to that particular area increases.

• 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).

• fMRI produces 3-dimensional images (activation maps) showing which parts of the brain are involved in particular mental processes.

• magnetic field - the fMRI machine creates a strong magnetic field around the person’s head.

• oxygen levels - measures these changes in oxygen levels in the blood (it can compare oxygen rich blood versus oxygen poor blood).

• images - the machine takes pictures of the brain and shows us which parts are using the most oxygen, indicating activity and are compared against a baseline of brain activity when not completing a task.

fMRI - strengths

• risk-free and non-invasive - does not rely on the use of radiation, so it is virtually risk-free, non-invasive and straightforward to use. Therefore, it can be used to measure activity in the brain without causing harm. It is also non-invasive, so there is no risk of infection or complications.

• high spatial resolution - shows detail by the millimetre, and therefore provides a clear picture of how brain activity is localised. It can show exactly which specific area is active during a specific task.

fMRI - weaknesses

• expensive - this means that many researchers can only use a small sample size, which impacts the validity and generalisability of the research.

• poor temporal resolution - it doesn’t show changes over time accurately so in a scan, areas may appear 4/5 seconds after the brain activity occurred, this means findings could be misinterpreted.

• cannot pinpoint exact activity of individual neurons - it can only measure blood flow in the brain, not exact activity so it can be difficult to tell what kind of brain activity is being represented on the screen.

EEG - knowledge

• they 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.

• the main 4 types of EEG waves are alpha, beta, theta and delta.

• scientists can also measure brain activity through amplitude and frequency. Amplitude = the intensity or size of activity. Frequency = the speed or quantity of activity.

• 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.

EEG - strengths

• helps diagnose conditions - e.g. epilepsy and schizophrenia, because the difference in brain activity can be detected on the screen, e.g. schizophrenic patients may display ‘unusual’ EEG wave patterns, which is useful for clinical diagnosis.

• useful applications - contributed to our understanding of the sleep stages and sleep problems.

• cheap - researchers can benefit from large sample sizes, therefore increasing the validity and generalisability of their studies.

• high temporal resolution - because it records brain activity in real time. Therefore, researchers can monitor responses to tasks.

EEG - weaknesses

• cannot detect activity in all regions - represents brainwave patterns and cannot detect activity in deeper brain regions, e.g. if there were issues to a patient’s hippocampus, an EEG wouldn’t necessarily pick up this information.

• not useful in pinpointing the exact source of neural activity - hard to work out which area of the brain the waves originate from.

ERPs - knowledge

• uses similar equipment to EEG (electrodes attached to the scalp) but, a stimulus is presented to a participant e.g. a picture or sound, and the researcher looks for activity related to the stimulus and can investigate how an EEG wave pattern changes in response to the stimulus, and the change is an ERP.

• the stimulus is presented hundreds of times and an average response is graphed. This is a statistical averaging technique, and it reduces any extraneous brain activity which makes the specific response to the stimulus stand out.

• research has revealed many different forms of ERP and how, they are linked to cognitive processes like attention and perception.

ERPs - strengths

• less general than EEGs - much more specific to the measurement of neural processes.

• provide a continuous measure of processing in response to a stimulus, which produces quantitative experimental data.

• able to identify ERPs of mental health issues like phobias. It has been found that people with phobias have ERP’s of a greater amplitude in response to images of the objects they feared compared to non-phobic individuals. This allows researchers more of an understanding of complex mental processes.

ERPs - weaknesses

• lack of standardisation in methodology between different research studies, which makes it difficult to confirm findings and the findings lack reliability.

• internal validity - not always possible to completely eliminate background noise and extraneous variables, which is needed to establish pure data in ERP studies.

post-mortem examinations - knowledge

• the analysis of a person’s brain following their death.

• 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 suffered. This may also involve comparison with a typical brain in order to determine the extent of the difference between them.

post-mortems - strengths

• vital in providing a foundation for early understanding of key processes in the brain - e.g. Broca’s and Wernicke’s areas were identified using post-mortems because neuroimaging did not exist at this time.

• improves medical knowledge and helps to generate hypotheses for further study.

post-mortems - weaknesses

• causation - observed damage in the brain may not be linked to the deficits under review but to some other unrelated trauma or decay, e.g. drugs and age may affect brain tissue. Therefore, there are issues with establishing a cause and effect relationship.

• ethical issues - difficult to get patient’s consent before death - a patient may have a significant brain abnormality when alive, and are therefore too ill to give consent for their brains to be investigated on when they die. This poses an ethical concern if a post-mortem is still carried out.