Windows into the Living Brain
For most of history the working brain was a black box. Modern imaging techniques opened it, dividing cleanly into two families: those that reveal structure (anatomy) and those that reveal function (activity).
| Technique | Measures | Reveals |
|---|---|---|
| EEG | Electrical activity | Function (millisecond timing) |
| CT | X-ray cross-sections | Structure |
| MRI | Magnetic fields | Structure (high detail) |
| fMRI | Blood-oxygen changes | Function (localizes activity) |
| PET | Radioactive tracer | Function (metabolic use) |
The fundamental trade-off in brain imaging is between temporal resolution (when things happen) and spatial resolution (where things happen).
Resolution and Pitfalls
EEG excels at timing, telling you when neurons fire, but struggles to pinpoint where. fMRI provides exquisite spatial detail by tracking the BOLD signal (blood-oxygen-level-dependent changes), locating activity within millimeters.
Common Pitfall: Treating fMRI as a direct measure of neural firing. It measures blood-oxygen changes that lag behind neural activity by a second or more. It is a metabolic proxy, not the electrical signal itself—which explains its poorer temporal resolution.