The key difference between EEG (electroencephalography) and fNIRS (functional near-infrared spectroscopy) lies in what they measure and how quickly they can measure brain activity: fNIRS measures neural activation on the order of seconds based on the hemodynamic response, while EEG measures electrical neural responses within milliseconds.
Here's a more detailed breakdown:
EEG (Electroencephalography)
- What it measures: EEG measures the electrical activity in the brain using electrodes placed on the scalp. It directly detects the ionic current flows within the neurons of the brain.
- How it works: Electrodes detect voltage fluctuations resulting from ionic current within the neurons of the brain. These fluctuations are amplified and recorded, providing a continuous record of brain electrical activity.
- Temporal Resolution: Excellent. EEG has a very high temporal resolution, measuring changes in brain activity in milliseconds (thousandths of a second). This makes it ideal for studying rapid cognitive processes.
- Spatial Resolution: Relatively poor. Determining the exact location in the brain where electrical activity originates can be challenging with EEG due to the blurring effect of the skull and scalp.
- Portability: EEG systems can range from research-grade stationary setups to more portable, battery-powered devices.
- Cost: Can vary, but generally less expensive than fNIRS systems.
- Susceptibility to Artifacts: Susceptible to artifacts from muscle movements, eye blinks, and electrical noise.
- Applications: Diagnosing epilepsy, sleep disorders, and brain injuries; monitoring brain activity during surgery; and researching cognitive processes.
fNIRS (Functional Near-Infrared Spectroscopy)
- What it measures: fNIRS measures brain activity indirectly by detecting changes in blood oxygen levels (hemodynamic response) in the brain.
- How it works: fNIRS uses near-infrared light to penetrate the skull and measures the absorption and reflection of this light by hemoglobin in the blood. Changes in the concentration of oxygenated and deoxygenated hemoglobin indicate changes in brain activity.
- Temporal Resolution: Good, but slower than EEG. fNIRS measures changes in brain activity on the order of seconds because it relies on the relatively slow hemodynamic response.
- Spatial Resolution: Better than EEG, but still limited. fNIRS can provide more localized information about brain activity compared to EEG, but it is still not as precise as techniques like fMRI.
- Portability: fNIRS systems are generally more portable than traditional fMRI machines, making them suitable for studies outside of a laboratory setting.
- Cost: Generally more expensive than EEG systems.
- Susceptibility to Artifacts: Less susceptible to electrical artifacts than EEG, but can be affected by head movements and changes in skin blood flow.
- Applications: Studying cognitive function, brain development, and neurological disorders; monitoring brain activity during rehabilitation; and brain-computer interfaces.
Summary Table
| Feature | EEG | fNIRS |
|---|---|---|
| Measures | Electrical activity of the brain | Changes in blood oxygen levels |
| Mechanism | Direct detection of neural activity | Indirectly measures neural activity through hemodynamic response |
| Temporal Resolution | Milliseconds (very high) | Seconds (good, but slower) |
| Spatial Resolution | Relatively poor | Better than EEG, but still limited |
| Portability | Variable, some portable systems exist | Generally more portable |
| Cost | Generally less expensive | Generally more expensive |
| Artifacts | Susceptible to electrical artifacts | Less susceptible to electrical artifacts |
In essence, EEG offers high temporal resolution, capturing the rapid dynamics of neural activity, while fNIRS provides better spatial resolution, offering more localized information about brain activity, albeit at a slower temporal scale. The choice between the two depends on the specific research question or clinical application.
