Qualitative and Comparative Cortical Activity Data Analyses from a Functional Near-Infrared Spectroscopy Experiment Applying Block Design

The interpretation of F-N-I-R-S, or fNIRS data, can be difficult for novice users as the data usually cannot be quantified. Our protocol using two complimentary methods provides a better understanding of this data. The main advantage of this technique is the increase and the reliability of the data analysis using two qualitative, GLM-based statistical parametric mapping and comparative hierarchical mixed models for multi-channels.

Before performing an fNIRS experiment, place the fNIRS device in a dark, noiseless area and place a whole head fNIRS recording cap onto the head of the subject, such that the position corresponding to the center of the international 10-20 system is located at the number 245 holder of the head cap. Attach the marking sticker to reference location points and take pictures of the subject's head with the probe locations, including the reference points from 15 perspectives. Arrange the 48-channel system with 32 optodes to a head cap bilaterally over the frontal and parietal areas as regions of interest and use the 3D digitizer software to determine the spatial registration.

After scanning picture data for the entire head, determine the spatial coordinates of the subject by auto measurement and save the data as Origin and Others files. To perform an fNIRS analysis, have the subject get into a comfortable position and instruct the subject to close their eyes. Then inform the subject of the start and stop cues and have the subject perform the block design task while maintaining the same upright posture for each task.

To use NIRS-SPM software to perform a qualitative general linear model analysis, start the NIRS-SPM program in the MATLAB software and select the NIRS system option from the pop-up menu. Select the Load button. To detect the spatial registration of the NIRS channel location, select the standalone and With 3D Digitizer checkboxes.

In the From Real Coordinates to MNI Space, use the dialog box to select the coordinate reference point and coordinate probes/channels files. Click Registration and select the points to proceed to the spatial estimation. Click OK and Project MNI Coordinate to Rendered Brain.

Select Dorsal View and click Save. In the Specify the 1st Level section, select the NIRS data filename and SPM directory. Check the hemoglobin checkbox and select specify design and sec.

Select vector of onset and durations and enter a vector of onset multiplied by the duration of the experimental conditions as indicated. For detrending, select Wavelet-MDL. Use the precoloring method, low-pass filter, and select hrf.

Correct for the serial correlation, select none. To estimate the temporal correlations, check Individual Analysis to analyze a single individual. To estimate the temporal correlations for a group of subjects, check Group Analysis, then compute the activation map based on the changes in hemoglobin level for the standardized brain.

To perform a multi-channel comparative analysis based on a hierarchal mixed model, open an appropriate statistical analysis software program and convert the text document of oxygenated and deoxygenated hemoglobin concentration changes in the nearest data file processed with the low pass filter to the spreadsheet software comma separated values file. Use the commands to create a pre-versus post-intervention import data for each subject and run the pre-and post-intervention data command for each channel as indicated. Based on the data obtained from the output results, enter the pre-versus post-intervention differences in change, rest, and on-task values of each channel in the spreadsheet.

Then enter the numerator and denominator degrees of freedom and the F and P values of the interact item of the fixed effect type three test to the spreadsheet. In this representative group analysis of 10 stroke patients, an increase in the cortical activity of the primary motor cortex was observed in the measured hemisphere immediately after the robot-assisted rehabilitation compared to that observed before the training. In this multi-channel group analysis comparing pre-versus post-intervention, an increased cortical activity was observed in the primary motor cortex after intervention, the same brain region as observed in the NIRS-SPM.

Our methods can be used to conduct pre-and post-intervention analysis for a variety of neurological disorders, such as movement disorders, cerebrovascular diseases, and neuropsychiatric disorders. Instead of elbow movements, researchers can also apply other block design tasks, such as leg movements. In addition, our protocol is useful for revealing treatment effects in various settings.