NEUROPSYCHOLOGY

Near infrared spectroscopy allows the imaging of brain activation by measuring changes in the concentration of oxy- and deoxy-hemoglobin (Hb). We have a Hitachi Optical Topography System ETG-4000 that can record up to 52 channels.

Infrared light can penetrate the scull and enter a few centimeters into the gray matter of the cortex. The NIRS system consists of two types of optodes, emitters and detectors that are placed on the scull. The emitters send infrared light through the scull that is partly absorbed and reflected back to the scull, where it is collected by infrared detectors. Depending on the oxygen content of the blood, the emitted infrared light will be absorbed differently.

Similar to fMRI, NIRS cannot measure the electrical activity of the brain directly. However, it indirectly indicates neural activity because of a close coupling between neural activity and local changes in blood flow and blood oxygenation. When nerve cells are active they consume blood-oxygen in the local capillaries. The neural activity itself and the oxygen consumption trigger subsequently a dilation of local capillaries, resulting in an increased inflow of highly- oxygenated blood. This hemodynamic response is comparatively slow, as it peaks after 4-6 seconds, before falling back to baseline in another 20 seconds.

Similar to fMRI, the numerous and evenly spaced optodes allow for a mapping of surface brain activity in two dimensions. Different from EEG where electrical activity measured on the surface of the brain could also stem from sources deep within the brain, the sources of the brain activity measured with NIRS have to be near to the surface of the skull.

The set of emitters and detectors can be placed on the scull similar to an EEG cap. The participants are therefore not as restricted in their body movements as within an MR scanner because NIRS is also comparatively robust with regard to body movement, as NIRS relies on optical measurements. This makes it a very valuable alternative method for studies with participants who have difficulties to sit still such as children. Another advantage of the NIRS system is its moderate size, which allows it to be transported and used in combination with other methods, as for example, the virtual reality environment.

Neuropsychology / Research Methods / NIRS


	Near infrared spectroscopy (NIRS)

	Near infrared spectroscopy allows the imaging of brain activation by measuring changes in the concentration of oxy- and deoxy-hemoglobin (Hb). We have a Hitachi Optical Topography System ETG-4000 that can record up to 52 channels. Infrared light can penetrate the scull and enter a few centimeters into the gray matter of the cortex. The NIRS system consists of two types of optodes, emitters and detectors that are placed on the scull. The emitters send infrared light through the scull that is partly absorbed and reflected back to the scull, where it is collected by infrared detectors. Depending on the oxygen content of the blood, the emitted infrared light will be absorbed differently. Similar to fMRI, NIRS cannot measure the electrical activity of the brain directly. However, it indirectly indicates neural activity because of a close coupling between neural activity and local changes in blood flow and blood oxygenation. When nerve cells are active they consume blood-oxygen in the local capillaries. The neural activity itself and the oxygen consumption trigger subsequently a dilation of local capillaries, resulting in an increased inflow of highly- oxygenated blood. This hemodynamic response is comparatively slow, as it peaks after 4-6 seconds, before falling back to baseline in another 20 seconds. Similar to fMRI, the numerous and evenly spaced optodes allow for a mapping of surface brain activity in two dimensions. Different from EEG where electrical activity measured on the surface of the brain could also stem from sources deep within the brain, the sources of the brain activity measured with NIRS have to be near to the surface of the skull. The set of emitters and detectors can be placed on the scull similar to an EEG cap. The participants are therefore not as restricted in their body movements as within an MR scanner because NIRS is also comparatively robust with regard to body movement, as NIRS relies on optical measurements. This makes it a very valuable alternative method for studies with participants who have difficulties to sit still such as children. Another advantage of the NIRS system is its moderate size, which allows it to be transported and used in combination with other methods, as for example, the virtual reality environment.