What is the primary difference between spatial resolution and temporal resolution in brain scanning?

Spatial resolution refers to the ability to distinguish the physical location of brain activity (the 'where'), while temporal resolution refers to the ability to track the timing of that activity (the 'when'). High spatial resolution provides a clear image of structures, whereas high temporal resolution provides a precise timeline of events.

How does fMRI differ from EEG in terms of what they actually measure?

fMRI is an indirect measure that tracks metabolic changes in blood oxygenation (the BOLD signal), whereas EEG is a direct measure that records the electrical fluctuations generated by neuronal firing. This makes EEG much faster at detecting changes but less accurate at locating them.

When would a researcher choose PET over fMRI despite the risks of radiation?

A researcher would choose PET when they need to study specific metabolic processes or neurotransmitter systems, such as dopamine receptor density. PET uses targeted radioactive tracers that can reveal chemical activity that fMRI, which only looks at blood oxygen, cannot detect.

What is a common misconception regarding the 'activity' shown in an fMRI scan?

A common error is believing fMRI shows real-time neural firing. In reality, fMRI measures the hemodynamic response (blood flow), which peaks several seconds after the actual neural activity has occurred, leading to a significant temporal lag.

Why is it incorrect to say that EEG can pinpoint activity in the amygdala?

EEG has poor spatial resolution because the electrical signals produced by deep brain structures like the amygdala must pass through the brain tissue, fluids, and the skull, which smears and distorts the signal. EEG is best suited for measuring activity on the surface of the cortex.

What mistake is made when assuming a PET scan is 'safe' for all participants?

PET scans involve the injection of radioactive isotopes, which poses a cumulative radiation risk. Therefore, it is generally avoided for children, pregnant women, or individuals who require frequent, repeated scans for longitudinal research.

Define the BOLD signal in the context of fMRI.

The BOLD (Blood-Oxygen-Level-Dependent) signal is the ratio of oxygenated to deoxygenated hemoglobin in the brain. Because oxygenated blood has different magnetic properties than deoxygenated blood, fMRI uses this ratio to identify which brain regions are currently active.

What are Event-Related Potentials (ERPs)?

ERPs are very small voltage changes in the brain that are triggered by specific events or stimuli. They are derived from EEG data by averaging many trials together to filter out background 'noise' and isolate the brain's specific response to that stimulus.

What is a 'tracer' in PET scanning?

A tracer is a biologically active molecule (like glucose or water) that has been tagged with a radioactive isotope. Once injected, it travels to the areas of the brain with the highest metabolic demand, allowing the scanner to map functional activity via gamma ray emission.

Why does fMRI have a 'temporal lag'?

The temporal lag occurs because fMRI measures the hemodynamic response—the movement of blood to active neurons—which takes about 2 to 5 seconds to peak. Since neurons fire in milliseconds, the blood flow change is a delayed reaction to the actual neural event.

The Use of Scanning Techniques to Identify Brain Functioning | AQA GCSE Psychology

Brain & Neuropsychology

The Use of Scanning Techniques to Identify Brain Functioning

Summary

Brain scanning techniques are neuroimaging methods used to visualize the structure and activity of the living brain. These tools allow researchers and clinicians to map cognitive functions to specific neural regions, diagnose neurological disorders, and understand the biological basis of behavior by measuring metabolic changes or electrical activity.

1. Definition & Core Concepts

Neuroimaging refers to the use of various techniques to either directly or indirectly image the structure, function, or pharmacology of the nervous system. It is a primary tool in cognitive neuroscience for linking mental processes to physical brain states.
Functional Imaging specifically focuses on the brain's activity during tasks or at rest, rather than just its static anatomy. It relies on the principle that active neurons require more energy, which triggers measurable changes in blood flow or electrical discharge.
Spatial Resolution describes the level of detail a scan can provide regarding the location of brain activity. High spatial resolution allows researchers to distinguish between small, adjacent structures in the brain.
Temporal Resolution refers to the accuracy of the scanner in terms of time, or how quickly it can detect changes in brain activity. High temporal resolution is necessary to capture the rapid firing of neurons which occurs in milliseconds.

2. Functional Magnetic Resonance Imaging (fMRI)

Mechanism of Action: fMRI measures brain activity by detecting changes associated with blood flow. It relies on the Blood-Oxygen-Level-Dependent (BOLD) signal, which identifies areas where oxygenated blood is replacing deoxygenated blood due to increased neural demand.
Hemodynamic Response: When a brain area is more active, it consumes more oxygen; to meet this demand, blood flow increases to that region. Because oxygenated and deoxygenated hemoglobin have different magnetic properties, the MRI scanner can map these metabolic shifts.
Strengths and Limitations: fMRI offers excellent spatial resolution (approximately 1-2 mm), allowing for precise localization of function. However, its temporal resolution is relatively poor (1-4 seconds) because the hemodynamic response lags behind actual neural firing.

A graph showing the trade-off between spatial and temporal resolution for fMRI, PET, and EEG. fMRI has high spatial but lower temporal resolution, while EEG has high temporal but low spatial resolution.

3. Positron Emission Tomography (PET)

4. Electroencephalography (EEG)

5. Key Distinctions

6. Exam Strategy & Tips