Functional near-infrared spectroscopy

Functional Near-Infrared Spectroscopy

A participant undergoing fNIRS measurement

Functional near-infrared spectroscopy (fNIRS) is a non-invasive imaging technique used to measure brain activity. It utilizes the near-infrared region of the electromagnetic spectrum to assess changes in blood oxygenation and blood volume in the brain, which are indicative of neural activity.

Principles

fNIRS is based on the principle that near-infrared light can penetrate biological tissues, including the skull, and is absorbed differently by oxygenated and deoxygenated hemoglobin. This differential absorption allows for the monitoring of cerebral blood flow and oxygenation.

Oxygenated vs deoxygenated red blood cells

Hemodynamic Response

When a specific region of the brain is active, it consumes more oxygen, leading to an increase in local blood flow to meet the metabolic demands. This process is known as the hemodynamic response. fNIRS detects these changes by measuring the absorption of near-infrared light by hemoglobin.

Absorption spectra of oxy- and deoxy-hemoglobin

Technology

fNIRS devices consist of light sources and detectors placed on the scalp. The light sources emit near-infrared light, which penetrates the scalp and skull, reaching the cerebral cortex. The detectors measure the intensity of light that is reflected back, which is affected by the concentration of oxy- and deoxy-hemoglobin.

Instrumentation

fNIRS headgear with Hitachi ETG-4000

The typical fNIRS setup includes a cap or headband with multiple optodes (light sources and detectors) arranged according to the 10-20 system. This arrangement allows for the mapping of brain activity across different regions.

International 10-20 system for EEG

Applications

fNIRS is used in various fields, including cognitive neuroscience, psychology, and clinical research. It is particularly useful for studying brain function in populations where other imaging techniques, such as fMRI, may be challenging, such as infants and patients with movement disorders.

Cognitive and Clinical Research

fNIRS has been employed to study cognitive processes such as language, attention, and memory. In clinical settings, it is used to assess brain function in conditions like stroke, traumatic brain injury, and neurodevelopmental disorders.

Advantages and Limitations

fNIRS offers several advantages, including portability, cost-effectiveness, and the ability to measure brain activity in naturalistic settings. However, it has limitations, such as limited depth penetration and lower spatial resolution compared to fMRI.

Related Pages

• Functional magnetic resonance imaging
• Electroencephalography
• Near-infrared spectroscopy