Functional Near-Infrared Spectroscopy for Recording Brain Activity During Social Interactions

Samenvatting

Source: Reindl, V., et al. Conducting Hyperscanning Experiments with Functional Near-Infrared Spectroscopy. J. Vis. Exp. (2019)

This video demonstrates the use of functional near-infrared spectroscopy (fNIRS) to measure brain activity during social interactions. Participants engage in a coordinated task that increases activity in the prefrontal cortex, a region critical for social behavior, while the system detects changes in light absorption due to blood oxygenation. By analyzing the synchrony of brain activity between participants, the study assesses neural dynamics underlying social interaction.

Protocol

All procedures involving human participants have been performed in compliance with the institutional, national, and international guidelines for human welfare and have been reviewed by the local institutional review board.

1. Preparation before the Participant Arrives

1. Prepare NIRS caps.
   1. Choose the cap sizes the same size or slightly larger than the participant’s head circumference.
   2. Cut 15 holes with a diameter of approximately 15 mm each, arranged in a horizontal 3x5 grid, into the forehead area of each of 2 raw electroencephalogram (EEG) caps. Make sure that the holes are spaced 30 mm from each other in any direction, that the middle column of holes is located in the center of the forehead, i.e., above the nose, and that the bottom row is located above the eyebrows.
   3. In order to make the caps more comfortable and minimize pressure marks, attach soft foam material (e.g., adhesive window sealing tape or similar flat foam rubber material) to the inner side of the holder grid between the probe sockets and at the edges. Use double-faced adhesive tape or sewing thread if necessary.
   4. Mount an empty 3x5 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.
      Note: The NIRS measurement system has two separate probe sets, use one probe set for each participant.
   5. Gently insert the probes into the appropriate holder sockets on the grids such that only the first ridge of each probe is mounted in the socket, which results in one clicking sound.
   6. Open the probe set monitor window at the NIRS measurement system and select 2 probe sets arranged in a 3x5 grid each, one for the participating child and one for the adult. Ensure that the probe arrangements of the two caps correspond to the arrangements in the probe set window (i.e., same location of the respective emitter and receiver probe numbers).
2. Prepare the experiment.
   1. Start the NIRS measurement system with laser diodes switched on 30 min. before measuring, such that the system reaches a stable operating temperature.
   2. Set all necessary options at the NIRS measurement system. Make sure that the device is set to event-related measurement and that the RS232 serial input, necessary for receiving triggers from the experimental paradigm, is active.
      Note: The experiment is an adapted version by a paradigm devised by Cui et al., programmed in the non-commercial Psychophysics Toolbox extensions, version 3.0.11.
   3. 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.
   4. Place two chin rests in front of the computer screen to prevent head movements during the experiment.

2. Participant Arrival in the Laboratory

1. Prepare the participants.
   1. Show and explain the experimental setup including the NIRS measurement system to the participants. Always make sure that the participants do not look directly into the laser beam of the NIRS measurement system as this may be harmful to the eye.
   2. 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.
   3. Instruct the participants and administer practice trials of both the cooperative and the competitive game. Give additional instructions during the practice trials if necessary.
   4. 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.
   5. Place the caps with the probes carefully on the participants’ heads, with the laser turned off. Place the front of the cap, including the probe grid, on the participant’s forehead first and then pull down the back of the cap towards the neck. Make sure that the middle probe of the bottom row is placed on Fpz and the middle probe column is aligned along the sagittal reference curve.
   6. 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. Use an additional holder (e.g., modified microphone stand or similar) for the second participant if necessary.
   7. Push each probe further into its socket until the small white nose in the center of the top of the probe casing is visible.
      Note: The nose is pushed upwards by a coil spring mechanism as soon as the probe tip touches the participant’s scalp.
   8. 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.
   9. If a channel does not have a sufficient signal (i.e., if it is marked in yellow), gently put the hair underneath the surrounding probe tip aside. If necessary, push the probes further into their sockets but ensure the comfort of the participant. Check whether the signal quality has improved (i.e., the channel is now marked in green) by clicking on the Auto Gain button again.
   10. If step 2.1.9. does not lead to a signal improvement, adjust the signal intensity. If there is too much signal (i.e., if the channel is marked in red), change the signal intensity to low signal intensity by repeatedly clicking on the respective probe’s symbol in the probe set monitor window of the NIRS measurement system. If there is not enough signal (i.e., if the channel is marked in yellow), change the signal intensity to high signal intensity, again by repeatedly clicking on the respective probe’s symbol.
2. Run the experiment
   1. When there are no questions after the practice trials and a good signal quality is ensured, start the experimental paradigm.
   2. Place a towel over the participants’ hands so that they cannot see the hand movements of their respective game partner.
   3. After the experiment, save the data and export the raw light intensity data as a text file by clicking on the Text File Out button. Do not apply any filters in the NIRS measurement system.
   4. Clean all necessary materials (probes, probe holders, chin rests) with ethanol. Wash the caps in a gentle cycle with mild detergent.

Materialen

Lijst van materialen gebruikt in dit artikel

Naam	Bedrijf	Catalogusnummer	Opmerkingen
NIRS measurement system with probe sets and probe holder grids	Hitachi Medical Corporation, Tokyo, Japan	ETG-4000 Optical Topography System	The current study protocol requires an optional second adult probe set for 52 channels of measurement in total as well as two 3x5 probe holder grids.
raw EEG caps	EASYCAP GmbH, Herrsching, Germany	C-SCMS-56; C-SCMS-58	Caps must be provided with holes for NIRS probes by the experimenter. Choose cap size the same size or slightly larger than participant's head circumference.
Technical computing software	The MathWorks, Inc., Natick, MA	MATLAB R2014a (or later versions)	Serves as base for Psychophysics Toolbox extensions (stimulus presentation), SPM for fNIRS toolbox (fNIRS data analysis), and ASToolbox (WTC computation).