Functional Near-Infrared Spectroscopy (fNIRS)
NIRS is a relatively young method that takes advantage of the fact that the blood oxygen (hemoglobin) absorbs light in order to situate cognitive and emotional processes in the brain. To measure the concentration of "used" blood (deoxygenated hemoglobin), and "fresh", not yet used blood (oxygenated hemoglobin) light from the near-infrared part of the light spectrum is radiated into the cortex. In proximity to the light source (about 3 cm) than it is measured how much light is absorbed. On the absorption of light by the hemoglobin thus, conclusions can be drawn about oxygen consumption of activated brain regions in by certain cognitive and emotional processes.
In comparison to fMRI, fNIRS can detect only brain regions that are up to 3 cm below the skull. Therefore, it is not possible to examine the most famous center of emotion, the amygdala. It is however powerfull enough to explore a region that is discussed in relation to a cognitive representation of emotion, the insula as well as the orbitofrontal cortex, which is proposed to be associated with concepts of the reinforcement-theory of emotion.
Furthermore, the spatial resolution is very limited in comparison to fMRI. The experimental effort with about an hour of preparation for mounting the optodes is certainly higher in comparison to fMRI. fNIRs is a relatively quiet method is therefore very good for the investigation of language. The method is also ideal to combine it with other methods. Event-related potentials for example, can easily be collected and evaluated simultaneously without major methodological effort as there are no artifacts triggered by a magnetic field. Finally, fNIRS is per se as harmful as the sunlight, since it shares the same near-infrared part of the light spectrum with it. For this reason, it can even be used for the study of newborns.
The D.I.N.E. hosts a standard DYNOT from NIRx. The DYNOT allows using 32 sources and 32 detectors, which covers almost the entire cortex. Using all sources of light, a time resolution of 1.9 Hz is achieved. If only one source is used, the hemodynamic response is recorded with a sampling frequency of 70 Hz. Therefore, the device is well suited to investigate the time course of hemodynamic response. The use of two wavelengths (760 and 830 nm) allows the simultaneous detection of oxygenated and deoxygenated hemoglobin. It is therefore particularly well suited to study the coupling of the hemodynamic parameters of the oxygen consumption and thus the excited blood "supply".
In particular scientists who intend to perform an fNIRS study are invited to contact Markus Hofmann (mhof[at]zedat.fu-berlin.de, scientific contact fNIRS laboratory).
Hofmann, MJ, Herrmann, MJ, Dan, I., Obrig, H., Conrad, M., Kuchinke, L., Jacobs, AM & Fallgatter, AJ (2008). Differential activation of frontal and parietal regions during visual word recognition: An optical topography study. NeuroImage, 40 (3), 1339-1348.