Spatial and temporal resolution

AQA expects you to know four ways of studying the brain: fMRI, EEG, ERPs and post-mortem examinations. Treat them as methods with different trade-offs, not as four interchangeable "brain scans".

The examiner will usually reward three kinds of thinking:

• AO1: accurate description of what the method measures and how it is carried out.
• AO2: choosing the right method for a research scenario.
• AO3: evaluating what the method can and cannot tell us about brain activity and behaviour.

Two key comparison terms run through the whole topic.

The other comparison is about time.

This matters because a method that is excellent at locating activity may be slower at showing timing, while a method that captures millisecond timing may be less precise about exact brain location.

AO2 example: If a researcher wants to know whether the visual cortex is more active during a visual task than a resting condition, a method with good spatial resolution is useful. If the researcher wants to know whether the brain responds 100 ms or 300 ms after a stimulus, a method with good temporal resolution is more useful.

fMRI: mapping active brain areas

fMRI maps a blood-oxygenation signal associated with neural activity in the living brain.

The key signal in fMRI is called BOLD.

When neurons in an area are active, they need more oxygen and glucose. Blood flow to that area increases, so fMRI can compare oxygenated and deoxygenated blood in active and less active states. The resulting image is often described as showing brain areas "lighting up", but that phrase is only a shorthand. fMRI does not directly record neurons firing; it records a haemodynamic response linked to neural activity.

AO1: what happens in an fMRI study

• The participant lies in a strong MRI scanner.
• They may complete tasks, respond to stimuli or rest while images are collected.
• The scanner detects BOLD changes across many small 3D units of brain tissue.
• Researchers compare activity across conditions, such as reading words versus looking at symbols.

AO2: when fMRI fits the research question

Suppose Priya wants to investigate which brain areas are more active when students silently rehearse a list of words. fMRI is suitable because it can show areas of increased blood flow across the brain during the rehearsal condition compared with a control condition.

AO3: strengths

• fMRI has good spatial resolution compared with methods such as EEG, so it is useful for linking tasks to particular brain regions.
• It is non-invasive and does not expose the participant to ionising radiation.
• It can study the living brain during psychological tasks, making it valuable for cognitive neuroscience.

AO3: limitations

• fMRI is an indirect measure of neural activity because it measures blood oxygenation rather than electrical firing.
• It has weaker temporal resolution than EEG or ERPs because the blood-flow response is delayed and spread over several seconds.
• It is expensive, noisy and sensitive to movement, so participants who move or feel uncomfortable in the scanner can produce lower-quality data.
• fMRI is correlational. If one area is active during a task, that does not prove the area caused the behaviour.

EEGs: recording electrical activity

Scalp electrodes record changing electrical potentials produced by populations of neurons.

In an EEG, electrodes detect tiny voltage changes produced by the summed activity of many neurons, especially the summed postsynaptic activity of similarly oriented cortical neurons. The record is continuous, so EEG is especially useful for studying broad patterns of brain activity over time.

AO1: what happens in an EEG

• Electrodes are attached to the scalp, often using a cap or conductive gel.
• The electrodes record electrical signals from the brain.
• The weak signals are amplified and displayed as wave patterns.
• Researchers or clinicians look for patterns linked to different states or abnormalities.

AO2: when EEG fits the research question

Suppose Jonah is investigating whether a stimulus changes overall electrical activity almost immediately after it appears. EEG is useful because it can record changes in brain activity with very high temporal resolution.

AO3: strengths

• EEG has excellent temporal resolution, often recording changes across milliseconds.
• It is non-invasive, generally safe and more practical than fMRI for many settings.
• It can record continuous brain activity rather than taking a delayed snapshot.

AO3: limitations

• EEG has relatively poor spatial resolution because scalp electrodes pick up activity from many brain areas and the signal is distorted as it passes through brain tissue, skull and scalp.
• EEG can be affected by artefacts such as eye movements, muscle activity and participant movement.
• It usually gives broad patterns of activity rather than clear evidence about a precise brain structure causing a behaviour.

ERPs: isolating responses to events

An ERP extracts the response associated with a particular event from ongoing EEG activity.

ERPs are not a separate machine from EEG. They are a way of analysing EEG data. Researchers record continuous EEG while a participant experiences repeated events, such as hearing a tone, seeing a word or pressing a button. They then cut the EEG into short sections around each event and average many trials together. Unrelated background activity is reduced by averaging, leaving a clearer response linked to the event. Averaging does not automatically remove a systematic artefact: blinking after every stimulus could remain time-locked, so contaminated trials and poor electrode contact must be checked.

AO1: what happens in an ERP study

• The participant wears EEG electrodes.
• A stimulus or response is presented many times.
• EEG is segmented into short epochs time-locked to each event.
• The epochs are averaged to reveal a waveform associated with the event.
• Components are often named by direction and timing, such as a positive wave around 300 ms.

AO2: when ERPs fit the research question

Suppose Amina wants to compare how quickly the brain detects a frequent word compared with an unusual word in a reading task. ERPs are suitable because they can show the timing of responses to the specific word event, even before a participant gives a spoken answer.

AO3: strengths

• ERPs have very high temporal resolution, so they are valuable for studying fast cognitive processes such as attention, perception and language processing.
• They are more specific than raw EEG because they isolate activity linked to a particular event.
• They are non-invasive and can reveal processing that may not appear in outward behaviour.

AO3: limitations

• ERP signals are very small, so researchers need many repeated trials and careful averaging.
• Artefacts from blinking, muscle movement or poor electrode contact can distort the signal.
• Like EEG, ERPs have weaker spatial resolution than fMRI, so they show when processing happens more confidently than exactly where it happens.
• Repeating many trials can make tasks less natural, which may reduce ecological validity.

Post-mortem examinations

Examination after death gives detailed tissue evidence that must be interpreted alongside records from life.

Post-mortem research can compare a person's brain tissue with clinical records, cognitive symptoms or behaviour observed while they were alive. This can involve examining visible damage, weighing or measuring brain areas, using microscopy, or analysing cellular and chemical features.

AO1: what happens in post-mortem research

• Researchers examine brain tissue after death, usually with prior consent or brain-bank arrangements.
• They look for abnormalities such as lesions, shrinkage, unusual tissue patterns or neurochemical differences.
• Findings are compared with the person's symptoms, abilities or diagnoses during life.
• Researchers may also compare tissue from people with and without a particular condition.

AO2: method in context

Henry Molaison, known as H.M., developed severe memory problems after surgery in 1953. Later post-mortem work on his brain used histological sectioning and digital reconstruction to refine understanding of the damage and remaining tissue. This shows how post-mortem evidence can add detail that could not be fully established during life.

AO3: strengths

• Post-mortem examinations can reveal detailed structural, cellular or chemical evidence that living scans may not show.
• They can be valuable when the person had a rare disorder or distinctive pattern of behaviour during life.
• They avoid causing harm to a living participant, provided consent and respectful tissue handling are in place.

AO3: limitations

• The person cannot complete new tasks, so researchers must rely on lifetime records, case notes or reports from others.
• Causation is difficult. Brain abnormalities found after death may have caused behaviour, resulted from illness, medication or ageing, or be unrelated.
• Samples can be small and unrepresentative because unusual cases are more likely to be studied.
• Tissue quality can be affected by factors such as time since death, disease history and storage conditions.

Matching methods to research questions

For AQA, the strongest answers do more than list strengths and weaknesses. They match the method to the question being asked.

AO2 method choice practice

• If the scenario asks where a task activates the brain, consider fMRI.
• If the scenario asks when electrical activity changes, consider EEG or ERPs.
• If the scenario asks about a specific repeated stimulus, ERPs are usually stronger than raw EEG.
• If the scenario asks about detailed tissue changes after death, consider post-mortem examination.

AO3 comparison moves

• fMRI and EEG/ERPs are all non-invasive methods for the living brain, but fMRI trades stronger spatial resolution for weaker timing.
• EEG and ERPs have strong temporal resolution, but ERPs isolate event-linked activity more precisely than a raw EEG trace.
• Post-mortem evidence can be rich and detailed, but it is retrospective and vulnerable to confounding variables.
• All methods need cautious interpretation. Brain-method evidence often shows association, not simple one-way causation.

Choosing a method and improving evidence

Suppose a study asks both where a reading process occurs and whether it differs 200 milliseconds after a word. fMRI addresses location; an ERP study addresses timing. Using both can give converging evidence, but their outputs are not interchangeable. Match the measurement to the precise aim before considering practical limits. For EEG/ERP studies, ask participants to minimise movement, monitor blinks and reject or correct contaminated epochs. These controls improve signal quality without turning an association into proof that one region causes reading.

Issues and debates

This topic links naturally to reductionism. Brain-study methods can explain behaviour in terms of neural activity or brain structure, which is powerful but can oversimplify if social, cognitive or environmental influences are ignored. It also links to determinism, because brain evidence may suggest behaviour is constrained by biology; however, method findings should not be overstated as proving that behaviour is fixed.