Functional MRI (fMRI)
fMRI measures brain activity by detecting changes associated with blood flow. This relies on the fact that cerebral blood flow and neuronal activation are coupled.
The BOLD Signal
Blood-Oxygen-Level-Dependent (BOLD) contrast is the standard technique. It utilizes the different magnetic properties of oxygenated and deoxygenated hemoglobin.
Limitations
- Temporal Resolution: Poor compared to EEG. The hemodynamic response takes several seconds.
- Spatial Resolution: Good, typically 1-3mm voxels, allowing mapping to specific anatomical structures.
- Indirect Measure: It measures blood flow, not direct neural activity (like action potentials).