Brain Scanning Techniques

Modern neuroscience relies on brain scanning techniques to study the structure and function of the brain. These techniques have transformed our understanding of the brain and its role in behaviour, cognition, and mental health. For GCSE Psychology, you need to know about the main scanning techniques and their strengths and limitations.

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Types of Brain Scan

1. PET Scan (Positron Emission Tomography)

PET scans measure brain activity by detecting the radioactive tracer injected into the participant's bloodstream.

Feature	Detail
What it measures	Brain activity — which areas are most active during a task
How it works	A radioactive tracer is injected; active brain areas use more glucose and receive more blood flow; the scanner detects the radiation
What it shows	Colour-coded images showing areas of high and low activity
Temporal resolution	Poor — shows activity averaged over minutes, not seconds
Spatial resolution	Moderate — can identify which brain regions are active

Used in: Tulving's memory study (showing different brain regions for episodic and semantic memory)

2. fMRI (Functional Magnetic Resonance Imaging)

fMRI scans measure brain activity by detecting changes in blood oxygenation (the BOLD signal — Blood Oxygen Level Dependent).

Feature	Detail
What it measures	Brain activity — which areas are most active
How it works	Active brain areas use more oxygen; the scanner detects changes in blood oxygenation
What it shows	Detailed images of brain structure AND activity
Temporal resolution	Better than PET but still limited (seconds, not milliseconds)
Spatial resolution	Excellent — very detailed images of brain structure
Radiation?	No — does not involve radiation

Used in: Maguire's taxi driver study (showing larger hippocampi)

3. EEG (Electroencephalogram)

EEGs measure electrical activity in the brain using electrodes placed on the scalp.

Feature	Detail
What it measures	Electrical activity (brain waves) across the whole brain
How it works	Electrodes on the scalp detect electrical signals produced by neurons
What it shows	Patterns of electrical activity over time (brain waves)
Temporal resolution	Excellent — records activity in milliseconds
Spatial resolution	Poor — cannot pinpoint exactly where in the brain the activity is occurring

Used in: Studying sleep stages, epilepsy diagnosis, detecting brain death

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Brain scanning techniques tree

graph TD
    A[Brain scanning techniques] --> B["Structural<br/>shows anatomy"]
    A --> C["Functional<br/>shows activity"]
    B --> B1["CT<br/>X-ray slices"]
    B --> B2["MRI<br/>magnetic field"]
    C --> C1["PET<br/>radioactive tracer"]
    C --> C2["fMRI<br/>BOLD signal"]
    C --> C3["EEG<br/>scalp electrodes"]
    C1 --> D1["Used by Tulving<br/>memory study"]
    C2 --> D2["Used by Maguire<br/>taxi drivers"]
    C3 --> D3["Sleep studies<br/>epilepsy"]

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Comparing Brain Scanning Techniques

Feature	PET	fMRI	EEG
Measures	Brain activity (metabolism)	Brain activity (blood oxygenation)	Brain electrical activity
Spatial resolution	Moderate	Excellent	Poor
Temporal resolution	Poor	Moderate	Excellent
Invasive?	Yes (radioactive injection)	No	No
Cost	Expensive	Expensive	Relatively cheap
Participant comfort	Injection required; must lie still	Must lie still in a noisy, narrow tube	Comfortable; can move relatively freely

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Evaluation of Brain Scanning

Strengths

• Brain scans provide objective, scientific evidence about brain function
• They allow researchers to study the living brain in action, rather than relying only on case studies of brain-damaged patients
• fMRI provides excellent spatial resolution, allowing detailed mapping of brain function
• EEG provides excellent temporal resolution, allowing researchers to track rapid changes in brain activity
• Brain scanning has important clinical applications (diagnosing tumours, epilepsy, stroke)

Weaknesses

• Brain scans show correlation, not causation — seeing activity in a brain region during a task does not prove that region causes the behaviour
• PET scans involve radiation, raising ethical concerns
• fMRI requires participants to lie still in a noisy, claustrophobic tube — this is uncomfortable and may not produce natural behaviour
• Brain scans can show which areas are active but cannot tell us exactly what the neurons are doing or what the person is thinking
• Results can be difficult to interpret — brain activity during a task may reflect many processes, not just the one being studied
• Most brain imaging studies use small samples due to the high cost of scanning

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Key Points

• PET scans measure brain metabolism using radioactive tracers — good for showing active areas but poor temporal resolution.
• fMRI measures blood oxygenation — excellent spatial resolution, no radiation, but requires lying still.
• EEG measures electrical activity — excellent temporal resolution but poor spatial resolution.
• Brain scans provide objective evidence but show correlation, not causation.
• Each technique has specific strengths and limitations — no single technique is perfect.

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Worked case study: Raine et al. (1997) — brain abnormalities in murderers

Aim: To investigate whether murderers pleading not guilty by reason of insanity (NGRI) showed structural or functional brain abnormalities compared with non-murderers, using PET scanning. This study is a landmark demonstration of how brain imaging can be used to study antisocial and criminal behaviour.

Procedure: Raine and colleagues recruited 41 murderers (39 male, 2 female, mean age 34.3 years) who had pleaded NGRI and were held in prison. They were compared to a matched control group of 41 non-murderers of the same age and sex. Two schizophrenics in the control group were matched with six schizophrenics in the experimental group to control for schizophrenia as a confound. All participants were injected with a radioactive glucose tracer and performed a continuous performance task (a visual attention task) for 32 minutes. A PET scan then measured relative glucose metabolism across brain regions.

Findings: Murderers showed reduced activity in the prefrontal cortex (important for impulse control and decision-making), reduced activity in the parietal lobes, reduced activity in the corpus callosum, and asymmetrical activity in the amygdala, hippocampus, and thalamus (reduced on the left, increased on the right). No differences were found in the caudate, putamen, globus pallidus, midbrain, or cerebellum.