8. ways of studying the brain

4 ways of investigating the brain

• functional magnetic resonance imaging (fMRI)

• electroencephalogram (EEG)

• event-related potentials (ERPs)

• post-mortem examinations

how does fMRI work?

it detects the changes in blood oxygenation and flow that occur as a result of neural activity in specific parts of the brain

Measures blood flow when a person performs a task

what happens 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

what do fMRIs show us?

fMRI produces dynamic 3D images showing which parts of the brain are highlighting which parts of the brain are involved in different neural activities- this has important implications for our understanding of localisation

strengths of fMRI

• virtually risk-free, non-invasive and straightforward to use. Unlike other scanning techniques like PET scans it does not use radiation. It can be used to measure brain activity without causing harm

• the images it produces have very high spatial resolution, of 1-2mm This provides a clear picture of how brain activity is localised.

weaknesses of fMRI

• expensive compared to other neuroimaging techniques

• poor temporal resolution (doesn’t accurately show changes over time). The highlighted areas appear 1-4s seconds after the brain activity has occured- findings can be misinterpreted.

• it can only measure blood flow in the brain, can’t tell us the exact activity of individual neurons. It can be difficult to tell what kind of brain activity is being represented- does not provide a direct measure of neural activity- cannot detect causation

what do EEGs measure and how?

electrical activity in the brain via electrodes that are fixed to an individual’s scalp using a skull cap

what do the scan recordings represent?

Small electrical changes are detected by the electrodes that are graphed over a period of time. Indicating level of activity in the brain

brainwave patterns that are generated from the action of millions of neurons, providing an overall account of brain activity

what are the 4 types of EEG waves?

alpha, beta, theta, delta

amplitude

intensity or size of activity

frequency

speed or quantity of activity

why are EEGs used by clinicians?

as a diagnostic tool as unusual arrhythmic patterns of activity may indicate neurological abnormalities (e.g. epilepsy, tumours or sleep disorders)

strengths of EEG

• valuable at helping diagnose conditions (e.g. schizophrenia and epilepsy) because the difference in brain activity can be detected on the screen- useful for clinicians

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

• extremely high temporal resolution (1-10ms) (unlike fMRI), it records brain activity in real time. Researchers can monitor responses to tasks.

• Non-invasive- no radiation- risk free

weaknesses of EEG

• it cannot detect activity in deeper brain regions as it only represents brainwave patterns. Therefore, if there were issues to a patients hippocampus an EEG would not necessarily pick up on this.

• not useful in pinpointing the exact source of neural activity so it is hard to work out which area ofthe brain the waves originate from- low spatial resolution , issues establishing causation

what is an ERP?

In an ERP a patient is presented with a stimulus (i.e. picture/sound) and researchers look for activity related to this stimulus and how an EEG wave pattern changes in response to the stimulus

what is the statistical averaging technique?

The stimulus is presented hundredes of the times and an average response is graphed. This reduces any extraneous brain activity, making the specific response to the stimulus stand out.

what has research revealed?

there are many different forms of ERPs and how these are linked to cognitive processes for example, such as attention or perception

strengths of ERPs

• ERPs are much more specific to the meaurement of neural processes than EEGs, partly addressing the problem of EEGs being too general- enable the determination of how processing is affected by a specific experimental manipulation -causation

• they provide a continuous measure of processing in response to a stimulus, this provides quantitative experimental data

what is a post-mortem examination?

technique involving the analysis of a dead person’s brain

in psychology, whose brain might be used in a post-mortem?

those of individuals who have a rare disorder and have experienced unusual deficits in mental processes or behaviour during their lifetime

why do psychologists want to examine brains after death?

in order to establish the likely cause of the affliction the person wihh brain damage suffered. This may also include comparison with a typical brain in order to determine the extent of the difference between them.

strengths of post-mortem

• post-mortem evidence was vital in providing a foundation for early understanding of key processes in the brain (e.g. Broca’s and Wernicke’s area)

• post-mortem studies improve medical knowledge and help generate hypotheses for further studies

weaknesses of post-mortem

• causation- observed damage in the brain may not be linked to the deficits under review but to some unrelated trauma or decay (e.g. age and drugs) Issues with establishing cause and effect

• ethical issues of consent from the patient before death- a patient may have a significant brain abnormality when alive and are therefore too unwell to give consent for their brains to be investigated

spatial resolution

smallest feature/meaurement that a scanner can detect

temporal resolution

how quickly the scanner can detect changes in brain activity