EEG vs fNIRS: A Technical Comparison
Comparing electrical vs hemodynamic measurements of cortical activity.
Measurement Modalities
Electroencephalography (EEG) measures the electrical fields generated by the synchronized firing of pyramidal neurons. Functional Near-Infrared Spectroscopy (fNIRS) measures the hemodynamic response—the change in oxygenated and deoxygenated hemoglobin associated with neural metabolic demand.
Temporal vs Spatial Resolution
EEG operates at the speed of light, providing millisecond-level temporal resolution (critical for BCI applications like P300 spellers). However, electrical fields smear as they pass through the skull, resulting in terrible spatial resolution.
fNIRS, using infrared light to penetrate the skull, offers significantly better spatial resolution (often ~1cm). However, the hemodynamic response is incredibly slow, peaking 5-7 seconds after the neural event.
Technical Specifications
| Modality | Signal Source | Temporal Res | Spatial Res | Portability |
|---|---|---|---|---|
| EEG | Electrical Potentials | ~1 ms | ~5-10 cm | High |
| fNIRS | Hemodynamics (Blood O2) | ~5 seconds | ~1-2 cm | Moderate |
Frequently Asked Questions
Can fNIRS be used for real-time BCI control?
Generally no. The 5-second hemodynamic delay makes it completely unsuited for real-time control (like flying a drone). It is better suited for state-classification (e.g., workload monitoring).
Next Steps
If you are building a BCI, use our BCI Bitrate Calculator to see how the temporal delay of fNIRS destroys information transfer rates compared to EEG.