Computational protocol: Neurofeedback Using Real-Time Near-Infrared Spectroscopy Enhances Motor Imagery Related Cortical Activation

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Protocol publication

[…] The NIRS-mediated neurofeedback system consisted of the NIRS system, a data-processing computer, and a monitor to display feedback information. A schematic overview of this system is illustrated in , and shows the system in use. To detect task-related hemoglobin signal changes, a continuous-wave NIRS system (OMM-3000, Shimadzu Corp., Kyoto, Japan) with 16 light emitter fibers and 16 light detector fibers was employed.It was assumed that NIRS detects hemoglobin signal changes derived from local vascular reactions coupled with neuronal activation at the cortical surface , , . In the present study, 5-ms pulses of near-infrared light at wavelengths of 780 nm, 805 nm, and 830 nm were emitted from each of the emitter fibers, respectively , , . Emitted light was absorbed by OxyHb and DeoxyHb and attenuated by scattering in tissues, which was detected by a detector fiber located 3 cm from each emitter fiber. OxyHb and DeoxyHb signal changes were calculated according to the modified Beer-Lambert Law for highly scattering media . For each wavelength, absorbance at the start of measurement was defined as the initial absorbance. Because it was not possible to measure the differential path-length factor using the continuous-wave NIRS system, it was assumed that it was constant, and hemoglobin signal changes were denoted in arbitrary units of millimolar-millimeter (mM×mm) .According to the fiber arrangement shown in , 50-channel measurements of hemoglobin signal changes from the frontoparietal skull surface were performed. As described in our previous study , a custom-made, hard-plastic cap, with an inter-optode distance of 3.0 cm, was used to hold the fibers tightly to the skull surface. For each subject, total experimental time using the NIRS system was not longer than 15 min. A light source at the center of the third row served as the anchor point and was placed at the subject's vertex (Cz). It was assumed that head sizes and shapes were comparable, because the hard-plastic cap fit well on all participants. Using this fiber arrangement, the C3 position was placed between the light detector at the leftmost of the third row and the light source at the leftmost of the third row (area of channel 9 in the ) in all subjects. Because the international 10–20 standard positions exhibit a certain level of standard deviation , and the NIRS system results in relatively low spatial resolution due to the banana-shaped propagation path of detected signals , it was assumed that the cortical location of each channel was comparable among participants. Therefore, the approximate cortical location of each channel was estimated from anatomical MRI data of representative subjects. Similar to our previous study , 3D T1-weighted MRI scans were obtained from two subjects, and the optode location was marked with a 3D digitizer (FASTRAK; Polhemus, Colchester, VT). After calculating the midpoint of the neighboring light source and detector on the skull surface, the fNIRS channel locations on the cortex were estimated using the balloon-inflation method . Anatomical normalization to the Montreal Neurological Institute (MNI) standard template was performed using 12-parameter affine transformation. In addition, the cortical region covered by each channel was estimated using MRIcro software (by Chris Rodan:, together with the Brodmann's area (BA) image and Automated Anatomical Labeling (AAL) image , which were downloaded from the website. Because the pre-segmented template images were aligned with normalized brain images in the MNI coordinate system, it was possible to estimate cortical regions and BA covered by each channel. Results from two representative subjects were comparable. […]

Pipeline specifications

Software tools MRIcro, AAL
Application Magnetic resonance imaging
Organisms Homo sapiens
Diseases Stroke