Task 7 - fNIRS and BCIs Flashcards
fNIRS (functional Near-Infrared Spectroscopy)
- Neuroimaging technique that measures brain activity by detecting changes in blood oxygenation levels.
- It works by shining near-infrared light through the scalp and skull
- The light is absorbed or scattered by oxygenated and deoxygenated hemoglobin in the blood
Optodes
Optodes are sensors that emit and detect near-infrared light. They are placed on the scalp to measure brain activity in fNIRS
Light absoprtion spectrum of oxygenated and deoxygenated hemoglobin
Oxygenated Hemoglobin (HbO₂): 650-900 nm.
Deoxygenated Hemoglobin (Hb): 750-850 nm.
Optical window
Most biological tissues are relatively transparent to light in near infrared range between 700-1000nm
This spectral band is called the optical window
Three types of fNIRS systems
- Continuous wave (CW) fNIRS
- Frequency-domain fNIRS
- Time-Resolved fNIRS
Continuous wave fNIRS
Three types of fNIRS systems
- Emits a constant (continuous wave) light at a fixed intensity.
- Measures how much light is absorbed and scattered by brain tissue.
- Most common and affordable
Frequency-domain fNIRS
Three types of fNIRS systems
- Uses modulated (pulsing) light instead of continuous light.
- Measures both light absorption and scattering, providing more accurate data.
Time-Resolved fNIRS
Three types of fNIRS systems
- Uses short laser pulses instead of continuous or modulated light.
- Measures how long it takes for photons to pass through brain tissue (time-of-flight analysis).
- Provides detailed absorption and scattering information.
- Most expensive
fNIRS Spatial resolution
- fNIRS has moderate spatial resolution (~1-3 cm), better than EEG but worse than fMRI.
- It’s limited to the outer cortex unlike fMRI
fNIRS temporal resolution
fNIRS has moderate temporal resolution (~1-10 Hz), better than fMRI but worse than EEG.
Brain-Computer Interface (BCI)
System that enables direct communication between the brain and an external device, bypassing the normal neuromuscular pathways
- Records brain activity (e.g., EEG, fNIRS, or invasive electrodes).
- Processes signals to detect brain patterns.
- Translates signals into commands for external devices (e.g., prosthetics, computers)
Neurofeedback
Neurofeedback is a form of biofeedback that teaches individuals to regulate their own brain activity.
* The BCI system monitors brain activity (via EEG, ECoG, or fNIRS).
* The system provides feedback (visual, auditory, etc.) on the brain’s current state.
* Users then learn to adjust their brainwaves to achieve desired outcomes (e.g., relaxation, focus, cognitive improvement).
Advantages of using fMRI for BCI
- Noninvasive
- Global brain coverage
- High spatial resolution
Disadvantages of using fMRI for BCI
- High cost
- Lack of portability
- Patient must stay still for extended time in supine position
- Susceptible to movement artifacts
- Lower temporal resolution compared to EEG
- No paramagnetic equipment allowed
Advantages of using fNIRS for BCI
- Noninvasive
- Portable
- Relatively low cost
- Nearly noiseless
- Less sensitive to movement artifacts than fMRI
- Easier to operate than fMRI
- No restriction on paramagnetic equipment
Disadvantages of using fNIRS for BCI
- Relatively new methodology
- Limited experience with BCI applications
- Limited spatial resolution (~3cm) Especially poor resolution of deep brain structures
- Susceptible to movement artifacts
Advantages of using EEG for BCI
- Noninvasive
- Portable
- Relatively low cost
- High temporal resolution (millisecond range)
- Silent
- Vast BCI experience
Disadvantages of using EEG for BCI
- Limited spatial resolution (~3cm)
- Especially poor resolution of deep brain structures
- Susceptible to artifacts from cranial muscles and eye movements
Locked-in syndrome
Rare neurological condition where a person is fully conscious and aware but unable to move or communicate due to complete paralysis of nearly all voluntary muscles, except for eye movements.
