EEG (electroencephalography) measures brain activity by detecting which of the following?
A: Changes in blood oxygen levels beneath the skull
B: Electrical activity produced by large groups of neurons, recorded via scalp electrodes
C: Magnetic fields generated by moving protons in brain tissue
D: The structural density of grey and white matter
Correct: Electrical activity produced by large groups of neurons, recorded via scalp electrodes
EEG records the summed electrical activity of millions of neurons via electrodes placed on the scalp. It has outstanding temporal resolution (milliseconds) but poor spatial resolution, because the skull and scalp blur the signal. It is non-invasive, relatively cheap, and widely used to study sleep, epilepsy, and the timing of cognitive processes.
What does fMRI (functional MRI) measure in order to infer brain activity?
A: The firing rate of individual neurons
B: Changes in electrical impedance across cortical layers
C: Changes in blood oxygenation (the BOLD signal)
D: The speed of cerebrospinal fluid circulation
Correct: Changes in blood oxygenation (the BOLD signal)
fMRI detects the BOLD (Blood-Oxygen-Level-Dependent) signal: active neurons consume more oxygen, triggering increased blood flow to that region. Oxygenated and deoxygenated haemoglobin have different magnetic properties, which the scanner detects. fMRI does not measure neural firing directly — it measures a vascular response that lags the actual activity by 4–6 seconds.
A researcher wants excellent spatial resolution to pinpoint exactly where in the brain a task activates. Which technique is most appropriate?
A: EEG
B: ERP
C: TMS
D: fMRI
Correct: fMRI
fMRI offers spatial resolution of around 1–3 mm, making it the gold standard for localising brain activity. EEG and ERP have millisecond timing but cannot reliably identify where the signal originates. TMS stimulates brain tissue rather than imaging it. For questions of "where?", fMRI wins; for questions of "when?", EEG/ERP wins.
Match each brain imaging technique to what it primarily measures.
MEG (magnetoencephalography) is similar to EEG in that it records neural activity in real time, but it differs because it measures:
A: Metabolic glucose consumption in active brain regions
B: The magnetic fields produced by electrical currents in neurons
C: Structural changes in white matter tracts
D: Radio-frequency signals emitted by protons
Correct: The magnetic fields produced by electrical currents in neurons
Whenever current flows in a neuron, it produces a tiny magnetic field perpendicular to the current. MEG detects these fields using superconducting sensors (SQUIDs) in a magnetically shielded room. Because magnetic fields pass through the skull undistorted (unlike electrical signals), MEG has better spatial resolution than EEG while retaining its millisecond-level temporal precision.
An ERP (event-related potential) is a separate brain imaging device distinct from EEG.
Answer: False
ERP is not a separate device — it is a data analysis technique applied to EEG recordings. By presenting a stimulus many times and averaging the EEG signal time-locked to each stimulus onset, the random background noise cancels out and a consistent waveform emerges. This waveform (the ERP) reflects the brain's electrical response to that specific event. Famous ERP components include P300, N400, and the mismatch negativity (MMN).
TMS (transcranial magnetic stimulation) is unique among these techniques because it:
A: Can temporarily disrupt or stimulate a specific brain region, not just observe it
B: Provides the highest spatial resolution of any non-invasive method
C: Measures the speed of nerve conduction along white matter pathways
D: Records the brain's response to auditory stimuli only
Correct: Can temporarily disrupt or stimulate a specific brain region, not just observe it
TMS delivers a rapidly changing magnetic field through the scalp, inducing an electric current in the underlying cortex. This can briefly excite or inhibit the targeted region. By disrupting a region and observing the behavioural effect, researchers can establish causal relationships — not just correlations — between a brain area and a function. This makes TMS invaluable for testing whether a region is necessary for a task.
fMRI measures neural firing directly and has a temporal resolution of a few milliseconds.
Answer: False
fMRI measures the haemodynamic response (blood flow changes) that follows neural activity, not the firing itself. The BOLD signal peaks 4–6 seconds after the neural event, giving fMRI very poor temporal resolution compared with EEG or MEG. Its strength is spatial precision (millimetres), not timing. Researchers often combine fMRI with EEG to get both spatial and temporal information.
Which of the following correctly describes the key trade-off between EEG and fMRI?
A: EEG is better at spatial localisation; fMRI is better at timing
B: fMRI is better at spatial localisation; EEG is better at timing
C: Both have equivalent spatial and temporal resolution
D: EEG can only be used during sleep; fMRI can only be used during movement tasks
Correct: fMRI is better at spatial localisation; EEG is better at timing
This temporal-spatial trade-off is one of the most important concepts in neuroimaging. fMRI can locate activity to within a few millimetres but its signal lags neural events by several seconds. EEG captures the brain's electrical response within milliseconds but cannot reliably pinpoint its source. Researchers designing studies must choose based on whether their question is about "where" or "when", or combine both techniques.
A structural MRI scan is most useful for which of the following purposes?
A: Measuring brain activity during a cognitive task in real time
B: Producing detailed images of brain anatomy, such as identifying tumours or structural abnormalities
C: Stimulating specific cortical regions to test causal function
D: Recording the timing of neural responses to sensory stimuli
Correct: Producing detailed images of brain anatomy, such as identifying tumours or structural abnormalities
Structural MRI uses magnetic fields and radio waves to produce high-resolution, three-dimensional images of brain anatomy. It is the standard clinical tool for detecting lesions, tumours, atrophy, and structural abnormalities. Unlike fMRI, it does not measure blood flow or activity — it captures a static anatomical picture. It is also used in research to measure regional grey matter volume and white matter tract integrity.
Brain Imaging Techniques
EEG (electroencephalography) measures brain activity by detecting which of the following?
About this quiz
Cognitive neuroscience depends on tools that let researchers see inside the living brain. Over the past century, a suite of techniques has been developed, each with different strengths: some capture the speed of thought in milliseconds, others reveal the precise location of activity down to a millimetre, and some can even switch a brain region on or off temporarily.
This quiz introduces the six most widely used methods: EEG, ERP, MEG, MRI, fMRI, and TMS. You will be asked to identify what each technique measures, how it works, and the key trade-offs between temporal resolution (how fast) and spatial resolution (how precisely located).
By the end you should be able to say confidently which technique a researcher would choose, and why, depending on what question they are asking.