How fNIRS technology enables hemodynamic response

Nick White
July 17, 2024
fNIRs in action
What is fNIRS and how does it enable brain training? How does fNIRS differ from technologies like EEG, and why is it particularly suited toward improving cognitive health?

fNIRS stands for functional near-infrared spectroscopy, which is a non-invasive optical technique that, following neuronal activation, allows the measurement of change in oxygenated (HbO2), deoxygenated (HbR), and total hemoglobin in brain tissue.

EEG, or electroencephalogram, is a test measuring electrical activity in the brain, indicative of brain cell communication, using small metal discs (electrodes) attached to the scalp.

fNIRS and EEG have different capabilities, making them suited to different functions.

While EEG is an important technology in detecting and diagnosing brain disorders, fNIRS offers numerous specific advantages over EEG, chief among them being the measurement of hemodynamic response.

Hemodynamic response refers to the rapid delivery of blood to active neuronal tissue. fNIRS makes use of the fact that oxygenated and deoxygenated blood absorb different proportions of near-infrared light.

fNIRS monitors brain hemodynamic changes indirectly via measuring the concentration changes: Δ[HbO2] (oxygenated hemoglobin), Δ[HHb] (deoxygenated hemoglobin), and total hemoglobin (i.e., the sum of oxygenated+deoxygenated). These measurements are secondary to the changes in local neural activity that lead to a corresponding oversupply of cerebral blood flow (CBF) to the functional localized area.

By monitoring changes in blood flow and oxygenation, fNIRS provides information complementary to, and yet different from, EEG.

Advantages of fNIRS technology.

As you likely know, the Thinkie System applies fNIRS (NIRS) technology. Other advantages presented by fNIRS are:

  1. Hemodynamic Insights: Highlights hemodynamic responses associated with brain activity, complementing other imaging techniques
  2. Comfort: fNIRS is non-invasive and generally more comfortable for participants compared to other neuroimaging techniques that require injection of tracers, exposure to strong magnetic fields, or placement of 20+ sensors requiring gel, paste, or a special cap to ensure proper connection
  3. Cost-Effectiveness: fNIRS devices are generally less expensive to purchase
  4. Real-Time Monitoring: Capable of providing immediate feedback on brain activity, making it exceedingly useful in interactive cognitive training
  5. Safe: Uses near-infrared light, which is long known to be safe for repeated use, making it suitable for studies requiring multiple sessions
  6. Portability: fNIRS systems are eminently portable and can be used in a variety of settings outside the laboratory, such as schools, clinics, homes and social settings
Summary of fNIRS and EEG capabilities.

fNIRS is uniquely suited to brain training, especially in relation to other, more cumbersome technologies, which may be better suited to clinical research and therapeutic applications. Among the more technical attributes that set fNIRS apart are:

  • Tolerant to Movement: fNIRS is less sensitive to movement artifacts compared to techniques like EEG, meaning the sensor-brain connection is more stable in a variety of positions and conditions. This flexibility makes fNIRS quite suitable for studies involving children, clinical populations, or activities that involve physical movement
  • Flexible application: Supports more ecologically valid experiments where subjects can be studied in naturalistic settings vs. the artificiality of a clinical setting
  • Spatial Resolution: Provides good spatial resolution for cortical surface activity, allowing detailed mapping of brain functions such as motor, sensory, and cognitive processes
  • Multimodal Studies: Enhances the robustness of findings when used alongside other techniques
  • Suitability for Young Participants: Particularly useful for research involving infants and children due to its non-invasive nature and tolerance to movement, which are critical in pediatric studies
Thinkie's portable sensor.

Thinkie is based on fNIRS, a technology with nearly thirty years1 of research and development supporting it. Experience the efficacy and ease of brain training with Thinkie today.

[1] fNIRS has been used extensively in myriad clinical applications, including brain training.

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