About NIRS - Basic Description
Functional near-infrared spectroscopy (fNIRS) is a specialized research optical imaging technique that uses near-infrared light to examine the function of the living brain. Research participants can be standing, sitting, lying down, or even engaged in active behaviors (walking, driving, exercising) while receiving an fNIRS scan. Small probes are placed on the top of the head using a cap. There is no sensation of any kind from the infrared light, and it is not harmful. An actual fNIRS scan typically takes less than one hour (depends on tasks). A participant might be asked to engage in a variety of activities during an fNIRS scan. Some activities might involve passively listening to sounds or seeing flashes, or performing learning, memory or other behavioral tasks. Participants might also be asked to play certain games or engage in activities on the computer or with an experimenter during the scan.
About NIRS - Detailed Description
NIRS can detect changes in relative concentrations of oxyhemoglobin and deoxyhemoglobin. Using this information, we can make inferences about metabolic consumption and brain activity. We can do this because while someone is performing a task there is increased cerebral blood flow (CBF) to the areas that are primarily being used to do that task. This process is referred to as neurovascular coupling.
NIRS caps have light sources that shine light through the scalp and into the brain. This light travels in a banana shape and is detected by light detectors that are also on the cap. Oxygenated and deoxygenated hemoglobin absorb light on a different frequency and we are able to collect this information to find the change of light absorbtion. We use a modified Beer-Lambert law equation to quantify the concentrations of oxygenated and deoxygenated hemoglobin and can then infer where there was higher concentrations of oxygenated hemoglobin which we infer to be areas of brain activity.