The aim of this study was to develop a working protocol to reveal the neuro activation pattern, underline the flanker task by using fused EEG and fNIRS neuro imaging technique. The simultaneous fNIRS EEG recordings allow for the inspection of the relationship between the of prefrontal cortex and different events related to the potential components of the whole brain. fNIRS in the cerebral cortex which pretty important law in study of cognitive processing.
We know that fNIRS is mostly used for inspecting the neurovascular activity in the frontal lobe. is related to high brain cognitive functions. However the haemodynamic response meted by fNIRS can only read the activities with low temporal resolution but EEG can offer temporary find and direct measurement of neuro activities.
The combination of EEG and fNIRS recordings is able to identify more features and reveal more information relate with the brain functions. In this study, you use the EEG fNIRS techniques were used for simultaneous recordings of ERP components and haemodynamic response with a flanker task. It's rational to assume that ERP components associate with the flanker task can exhibit significant correlation with the haemodynamic response.
To tether this assumption, the fNIRS set up and the EEG machine were integrated together to reveal the complex neuro cognition metism corresponding to the event with flanker task. Prior to the experiment test, all participants signed informed consent documents. The study was approved by the ethics committee of the University of Macau.
Number one, hardware and software setting for concurrent EEG and fNIRS recordings. Construct a feasible head cap for concurrent EEG and fNIRS recordings. Select the right cap size according to the head circumference of participants.
In this study, a medium-sized cap is used since it's suitable for most adolescent or adult participants. Draw the layout according to the experiment design in the literature. Dig 22 holes inside the EEG cap for holding fNIRS optodes in line with a specifically out frontal cortex.
Place 21 or 71 EEG electrodes along the surface of the EEG cap according to the 10-20 international system and mount the grates for the optodes. Set the distance between each source detector pair as three centimeters and then fix the optodes. In each the blue optodes are detectors while the red ones are laser sources.
Setting the EEG and fNIRS port in the software. Set the parallel port, example H378 in this study for the EEG system. Set the serial ports, example 600 in this study for the fNIRS system.
The port type and number should be modified regarding various EEG and fNIRS setups. Please contact the manufacturers for more information. Preparation before the experiment.
Warm up the fNIRS system with lasers. Switch it on for 30 minutes. Set all necessary operation permitters for the fNIRS measurement system.
Should the setup, including the EEG and fNIRS measurement systems to participant. Measure and mark the CZ point according to the 10-20 international system. Identify the electrode position of CZ at half of the distance between the and half of the distance between the left and right interorbital indentations.
Place the front part of the cap along the participants forehead first and then pull down the back session of the cap towards the neck. Validation the positions. Note, it is highly recommended that EEG electrodes should be firstly set and subsequently the nearest optodes.
If EEG conductive gel covers the holes for the placement of nearest optodes it should be clean to prevent the contamination of optodes. Preparation for the EEG recordings. Fill conductive gel by inserting a blunt needle through the holes of EEG electrode grate.
Place all electrodes into the EEG electrodes grid according to the levels. Open the EEG software and inspect the signal quality of the electrodes. Readjust electrodes by refilling conductive gel if the signal quality could not meet the requirements.
Preparation for the fNIRS recordings. Caution do not expose participants eyes to laser beam of the source directly. Place the optical fibers along the holder arms attached to the fNIRS measurement system and additional holder.
Make sure that the fibers are neat and tidy. Insert the optical source and detectors into the holes according to the layout. Test the signal quality.
If a channel does not have a high level signal to noise ratio. Example, if the channel is marked in yellow gently swap participant hair surrounding the optical probes to ensure that nothing exists between the optical probe and skull. If step 2.8.3 cannot improve the signal quality turn up the signal intensity.
If there is too much signal. Example if the channel is marked in red, turn down the signal intensity. Run the experiment.
Start the experiment when the signals are stable with excellent signal to noise ratio and participants are familiar with the experiment instructions. After the experiment, save and export the data off the EEG fNIRS. Remove EEG electrodes and fNIRS optical probes carefully.
Measurement of three dimensional, 3D MNI coordinates of fNIRS optodes with 3D digitizer. Let participants sit in a chair and wear the glasses with a sensor. Open the digitizer software on the computer.
Ensure that the 3D digitizer system is in connection with the computer through an appropriate com port. Load the layout of optodes set in file. Move the 3D digitizer styles accord the key positions.
NZ, LZ, left ear, right ear, CZ along the screen and press the button on the stylus. Localize optical source and detectors. Export the 3D coordinates file.
Data analysis. fNIRS data analysis. Process the 3D MNI coordinates file by using the registration option in fNIRS SPM with MetLife 2019.
Select stand alone special registration with 3D digitize. Choose the previously, save it others and origin text file.Registration. Pre-process fNIRS signals with Homer2 software according to the following steps.
The application of the modified Motion artifact correction. Then pass filtering 0.015 hertz to 0.2 hertz. Normalize a more dynamic signal amplitude by dividing the average values.
Generate the fNIRS data for each channel basing on a 3D digitized information. Select the channels that has a registration probability of 100%or more in SFC according to the regression calculation of the fNIRS SPM for further analysis. Export the peak values of HbO.
EEG data processing. Load the raw EEG data folder into the EEG lab by using the plugins. Choose the BOC plugin for BDF file in this study.
Note, please choose suitable plugin according to the EEG data file format. Set the channel location information for EEG lab. Load the corresponding location file of the cap.
We reference in electrodes in ERP lab which is one plugin of EEG lab. Choose the channels, place it in the mass storage as referenced electrodes. Extract EEG data based on the event and bin files in the ERP lab.
Filter the EEG data segment in the ERP lab by using the IIR filter. By filtering the low frequencies with a cutoff of 30 Hertz and by filtering the high frequencies with a curve of 0.1 Hertz. Remove ocular EEG artifacts within Bendon component analysis in EEG lab.
Reject EEG data segment with amplitude values exceeding the range from positive 100 to the negative 100 microvolt at any channel in ERP lab. the EEG data segment in ERP lab. Note, these are the generally used data analysis method and the software for pre-processing EEG and fNIRS data.
There are numerous processing software and methods available. Correlation calculation. Generate the relationship between fNIRS and EEG recordings with Pearson correlation analysis.
Representative results. fNIRS headset placement and channels configuration. The digitized optodes layout are converted into the MNI coordinate system and overlapped along the brain cortex.
HbO signal for all channels associated with the flanker task. The pink curves denoting congruent condition while the green ones indicate the congruent condition. ERP signal for FZ and FCZ electrodes.
The black curves define the incongruent condition while the red ones denote the congruent condition. Correlation between the ERP N200 and fNIRS signal along the SFC for the incongruent condition. In summary combine the EEG and fNIRS neuro imaging was performed to map the brain activation involved flanked by recording the neuro signals of whole brain and haemodynamic response of the prefrontal cortex.
We successfully acquired the EEG and fNIRS data with a flanker task. Our finding showed that the fNIRS haemodynamic response and ERP N200 components are significantly correlated which exhibit different perspective of cognitive mechanism associated with the flanker task. Our multimodal neuro imaging results support a essential roles of combined the EEG and fNIRS technique in contributing to brain which paves a new avenue for improving the understanding of neuro mechanism of different cognitive processing.
