This study investigates brain-to-brain synchrony during cooperative and competitive tasks using functional near-infrared spectroscopy (fNIRS). Participants, consisting of a parent-child dyad, engage in visual stimuli tasks while their brain activity is monitored.
Begin with a parent-child dyad fitted with probe grids of a functional near-infrared spectroscopy, or fNIRS, system and positioned in front of a shared display.
Emitter probes in the grid emit near-infrared light, which penetrates brain tissue.
As a baseline, when no stimulus is present, the blood in the cerebral vessels maintains normal metabolic oxygen levels.
Record the baseline activity by measuring the reflected light detected by the detector probes.
Introduce a visual stimulus that requires the participants to respond by pressing buttons in either cooperation or competition, resulting in increased activity in the prefrontal cortex, a brain region crucial for social interaction.
Increased neuronal activity elevates the metabolic oxygen demand, triggering the flow of oxygenated blood carrying oxyhemoglobin.
A change in light absorption by the increased oxyhemoglobin reflects the increased activity.
Analyze the co-occurrence of increased activity between the participants during the task to assess brain-to-brain synchrony.
Begin by choosing a cap size that is the same size or slightly larger than the participant's head circumference. Cut 15 holes, with a diameter of approximately millimeters each, arranged in a horizontal 3 by 5 grid into the forehead area of each of 2 raw EEG caps. Ensure that the holes are spaced 30 millimetres from each other in any direction, that the middle column of holes is located in the center of the forehead. In order to make the caps more comfortable and minimize pressure marks, attach soft foam material at the inner side of the holder grid between the probe sockets and at the edges.
Next, mount an empty 3 by 5 probe holder grid to each of the modified EEG caps, such that the holder grid itself is placed on the inside of the cap, and the holder sockets stick in the holes. Then, gently insert the probes into the appropriate holder sockets on the grid, such that only the first ridge of each probe is mounted in the socket, which results in 1 clicking sound.
Open the probe set monitor window at the nearest measurement system, and select 2 probe sets arranged in a 3 by 5 grid each. One for the participating child and one for the adult. Ensure that the probe arrangements of the two caps corresponds to the arrangements in the probe set window. Next, switch on the laser diodes of the NIRS measurement system 30 minutes before measuring, so that the system reaches a stable operating temperature.
Set all the necessary options at the NIRS measurement system. Make sure that the device is set to event related measurement, and that the RS-232 serial input necessary for receiving triggers from the experimental paradigm is active. Then, prepare the experimental paradigm by starting the technical computing software that serves as base for the psychophysics toolbox extensions and setting the current directory to the folder that the paradigm is saved in. Finally, place two chin rests in front of the computer screen to prevent head movements during the experiment.
Begin by escorting the two participants into the testing room and explaining the experimental setup. Then, seat the participants next to each other in front of the computer screen. Adjust the height of the chin rests, such that both participants sit comfortably. Provide instructions and administer practice trials of both the cooperative and the competitive game.
Next, measure and mark the FPZ point according to the 10-20 system, which is 10% of the distance between nasion and inion on each participant's head. Then turn off the laser, and place the caps with the probes carefully on the participants heads. Ensure that the middle probe of the bottom row is placed on FPZ, and the middle probe column is aligned along the sagittal reference curve. Place the fiber strings on the holder arm attached to the NIRS measurement system, so that they hang loosely without contact with the participant or chair, and that they do not pull on the caps.
Next, push each probe further into its socket until the small white nose in the center of the top of the probe casing is visible. Then, turn the laser on again and test the signal quality by clicking on the Auto Gain button in the probe set monitor window of the NIRS measurement system. If a channel is marked in yellow, meaning insufficient signal, gently put the hair underneath the surrounding probe tip aside.
Make probe adjustments and click the Auto Gain button again to see if signal quality has improved or is marked in green. Once the signal quality is satisfactory, place a towel over the participants hands so that they cannot see the hand movements of their respective game partner. Then start the experiment. Then after the experiment is complete, save the data and export the raw light intensity data as a text file by clicking on the Text File Out button.
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