The term "neurofeedback" typically refers to EEG (brainwave) technology, which has been in use for about a century. Thinkie's NIRS technology, on the other hand, is relatively new—about 30 years old—and not as widespread in the U.S. as it is in Japan (Thinkie is a Japanese company). Here's a basic breakdown of the differences between EEG and fNIRS and how they're used for different purposes.
- Definitions
EEG (Electroencephalography) and NIRS (Near-Infrared Spectroscopy) are both non-invasive techniques used to monitor and study the brain, but they measure different aspects of brain activity and function based on distinct principles. Here's how they compare and where NIRS holds advantages over EEG:
2. Principle of Operation
- EEG measures the electrical activity of the brain. It detects fluctuations in voltage resulting from ionic current flows within the neurons of the brain. EEG sensors are placed on the scalp to capture these electrical signals, which are then analyzed to infer brain activity patterns.
- NIRS, on the other hand, uses near-infrared light to measure changes in blood oxygen levels within the brain. It evaluates the absorption of light by oxygenated and deoxygenated hemoglobin, providing insights into cerebral blood flow and oxygenation, which indirectly reflect brain activity.
Advantages of NIRS Over EEG
1. Insensitivity to Electrical Artifacts: NIRS is not affected by electrical artifacts such as muscle movements, eye blinks, or electrical interference from external sources, which can significantly contaminate EEG signals. This makes NIRS more suitable for studies involving motion or in environments with potential electrical noise.
2. Spatial Information on Cerebral Blood Flow: NIRS provides spatial information about cerebral blood flow and oxygenation levels, offering insights into which areas of the brain are more active in terms of metabolic demand. While EEG provides high temporal resolution of brain electrical activity, it lacks precise spatial resolution due to the blurring effect of the scalp and skull on the electrical signals.
3. Non-contact with the Skin: Some NIRS devices can operate without direct contact with the skin, which can be advantageous in studying populations with sensitive skin (e.g., infants or individuals with skin conditions). EEG, in contrast, requires direct contact with the scalp and often uses conductive gels, which can be inconvenient or cause discomfort.
4. Better Penetration Depth: NIRS can probe deeper into the brain than EEG, reaching cortical and subcortical structures, although its penetration is still limited compared to imaging modalities like MRI. EEG signals originate primarily from the cerebral cortex and offer little to no information about activities in deeper brain structures.
5. Monitoring Cerebral Oxygenation and Hemodynamics: NIRS provides unique insights into the brain's oxygenation status and hemodynamic changes, which are vital for understanding cerebral metabolism and vascular responses. This aspect of brain function is something EEG cannot directly measure, as EEG focuses solely on electrical activity.
3. Applications and Use Cases
While EEG is extensively used for diagnosing epilepsy, sleep disorders, and other neurological conditions due to its excellent temporal resolution of brain's electrical activity, NIRS is particularly advantageous in research settings where understanding the relationship between neural activity and cerebral blood flow is crucial, such as in cognitive neuroscience and brain-computer interfaces. NIRS is also increasingly used in clinical settings for monitoring the brain's oxygenation levels in critical care, neonatology, and during surgical procedures where blood flow and oxygenation are critical.
In summary, NIRS offers complementary information to EEG by providing insights into cerebral blood flow and oxygenation, which are indicative of the brain's metabolic demands and vascular health. This makes NIRS particularly valuable in studies and applications where these aspects are of interest.