Modern psychology uses several techniques to study the living brain. Each has trade-offs in invasiveness, temporal resolution (how precisely it captures when something happens) and spatial resolution (how precisely it captures where).
Post-mortem studies
The oldest method: examine the brain after death, usually of a person whose unusual behaviour was documented in life. Broca and Wernicke worked this way.
- Strength — gives detailed view of structures (down to the cellular level with staining).
- Limitation — cannot show function; results are correlational (we see damage but can't directly link it to specific behaviour); confounded by cause of death and age-related decline.
CT (Computerised Tomography) scans
A series of X-rays from different angles, combined into a cross-sectional image of the brain.
- Strengths — quick, widely available, good for identifying tumours, bleeding and skull fractures.
- Limitations — uses ionising radiation; only shows structure, not activity; lower resolution than MRI.
PET (Positron Emission Tomography) scans
A radioactive tracer (often glucose-tagged) is injected; active brain regions take up more glucose, emitting positrons that the scanner detects.
- Strengths — shows brain function (the active regions during a task); good for studying neurotransmitter activity (e.g. dopamine in addiction).
- Limitations — invasive (radioactive tracer); poor temporal resolution (images take ~30 seconds to build up); expensive.
fMRI (functional Magnetic Resonance Imaging)
Uses powerful magnets to detect changes in blood oxygen levels (the BOLD signal). Active neurons need more oxygen, so blood flow increases there.
- Strengths — non-invasive (no radiation, no injection); excellent spatial resolution (~1 mm); shows function in real time across the whole brain.
- Limitations — temporal resolution still 1–5 seconds (slow compared with the actual neural events, which are milliseconds); expensive; participants must stay very still; claustrophobic; only correlational evidence.
Comparing the methods
| Method | What it shows | Resolution | Invasive? |
|---|---|---|---|
| Post-mortem | Structure (very detailed) | Cellular | After death only |
| CT | Structure | Moderate | Some radiation |
| PET | Function (metabolism) | Moderate spatial, poor temporal | Yes (radioactive tracer) |
| fMRI | Function (blood flow) | High spatial (~1 mm), moderate temporal | No |
Choosing a method
A researcher studying which area is active during a task should choose fMRI. A researcher studying neurotransmitter levels should choose PET. A clinician investigating a possible bleed should use CT for speed. Detailed structural neuroscience uses post-mortem when possible.
⚠Common mistakes— Common errors
- Confusing CT with MRI — CT uses X-rays, MRI uses magnets.
- Saying fMRI shows neural activity directly — it shows blood-flow changes, which lag behind neural firing.
- Forgetting that all live-brain-imaging methods produce correlational evidence: they show association, not causation.
AI-generated · claude-opus-4-7 · v3-deep-psychology