-------------------- Operational Protocol -------------------- **Authors:** Gayathri Satheesh `gs2750@nyu.edu `_, Maitha Al Shaali `ma6895@nyu.edu `_, Haidee Paterson `haidee.paterson@nyu.edu `_, Hadi Zaatiti `hadi.zaatiti@nyu.edu `_ Based on a previous version of the protocol from Aniol Santos Angles. - Find a PDF version of the protocol: `MEG Lab manual PDF download `_ - Once you master the current protocol, keep in handy the :ref:`MEG Session Checklist ` .. contents:: :local: :depth: 2 :backlinks: entry Lab booking and schedule ------------------------ .. warning:: Bookings should not take place on a Monday morning, as this is when Helium refills are scheduled and it is not possible to acquire data during this period. Checks Completed by MEG Scientist Prior to Experiment ----------------------------------------------------- The MEG lab is provided to the project owner after the following checks and tests have been performed successfully. #. KIT system is in an operational status when: - Helium levels are sufficient to conduct an experiment - Quality of the data from SQUIDs sensor has been verified - Empty-room data has been acquired and noise levels have been computed and assessed #. Vpixx system is operational when: - Trigger events are tested - Projector is in a running state - Response boxes must be tested for correct button responses #. Communication system with participant are operational when: - Microphone outside the MSR, to communicate to the participant works correctly - Microphone inside the MSR for participant to communicate with project owner works correctly - Earphones with disposable single use foam earplugs for participant to hear the project owner outside the MSR works correctly - Camera inside MSR for visualising the participant #. Laser scanner system is operational when: - Laser scanner computer works correctly - Laser pointer/surface scanner is operational #. Personal Protective Equipment/Clinical Consumables are available including: - clean foam earplugs - head caps - scrubs - clinical application tape for HPI coils on participant face - gloves - linen - face baby wipes - normal tissue paper - head caps - kitchen towels - glasses for vision correction -6 to +6 in 0.5 increments - a sign to be used if the participant is a female wearing a veil/head covering Should you require new items please contact the team with your request. Performed by the project owner - Prepare the lab equipment (prior to participant arrival) ----------------------------------------------------------------------------------------- The steps below should be **performed by the project owner** prior to the arrival of the participant and should be completed in the following the order. These procedures take an estimated time of 20 mins. #. Prepare MSR: - Make sure the MSR has no metal objects inside - Switch the heater off .. figure:: figures/meg-operationprotocol/heater.png :alt: Heater Button Image :align: center :scale: 40% Heater Button - Prepare bedsheets and pillowcases - Clinical Tape is usually stored in the drawers inside the plastic drawers inside the MSR - or/also in the top right wooden drawer outside the MSR, on the right side of the `Stimulus computer` - Prepare 12 pieces of tape, those will be used to set the `HPI coils` on the participant's head #. Marker box check: - Ensure that the `Marker Box` found inside the MSR has enough battery - Power up the `Marker Box` by flipping the `Power` switch up - If there is enough battery, the red LED 'Low batt' should go on for a second and then back off - If there is not enough battery, the red LED 'Low batt' is either on all the time or never comes on for a second as previously - In this case, change the batteries of the Box, recharged batteries are available under the `Stimulus` computer .. figure:: figures/meg-operationprotocol/Marker_box_power.png :alt: Trigger Box :align: center :scale: 60% Marker box power indicator - Uncoil the five HPI marker coils that are linked to the `Marker Box` #. Trigger Box preparation: - The `Trigger Box` is outside the MSR and pictured below .. figure:: figures/meg-operationprotocol/trigger_box.png :alt: Trigger Box :align: center Trigger Box found above the `MEG Main PC`. - Ensure that the `Source` button is set to `LPT1/PC` which is on the left side #. If project owner requires empty-room data prior to experiment: - Turn off the MSR lights and put the light brightness to low - Close the MSR door without a particpant inside - After the previous steps, on the `MEG Main PC` computer, open `MEG160` software - Then, Menu -> Acquire -> Auto Tuning -> Ok - Wait for the auto-tuning to be done - From Menu -> Acquire -> MEG Measurement -> Monitor and Acquisition window should open - In the 'Sensor Control' window ensure or set these parameters *NB are only to be used for empty-room data and not for a neuro-activity experiment measurement)*: - HPF to `0.1 Hz` - LPF to `1 KHz` - BEF to `THRU` - Click on 'Sensor Check' - Let the Sensor Check run for around 30 seconds - Uncheck 'Sensor Check' - Make sure that the sensor display identical sinusoidal wave - Remember that `Sensor 91` is broken and will not display a sine wave - In the ‘Data Acquisition’ window enter the following: - Patient ID: sub-emptyroom - Name: sub-emptyroom_ - Foldername: C: \MEG160\Bin\emptyroom - After ensuring the MSR door is closed, press `Lock` - The sensor measurements will oscillate rapidly, wait until the values are stable, i.e., no upward or downward trend is observed - Continuous Mode -> Start - Set Sampling Rate to 2000 Hz - Set Time to `180 seconds` - then, `Start Acquisition` - When recording is done, press `Unlock` - Close the `MEG Measurement` window - Open the MSR door #. Prepare Vpixx systems: - Ensure that the three `Vpixx` boxes are turned on: Soundpixx, Propixx and Responsepixx - Soundpixx box - all the knobs have to be set as a default to the positions on the image below: .. figure:: figures/meg-operationprotocol/soundpixx.png :alt: Soundpixxbox settings :align: center :scale: 30% Soundpixx Box knob settings - Turn on the computer if it is off, boot under Windows (it will default to Ubuntu) - Settings of Vpixx computer. Ensure that: - Screens are in multiple displays (not mirror display) - Right-click on desktop > Display settings > Extend these displays > Keep changes - Set up Vpixx either through the LabMaestro platform (preferred) or through bash script **VPutil** GUI - **LabMaestro** - Open `LabMaestro` found on the desktop .. figure:: figures/meg-operationprotocol/LabMaestro_icon.png :alt: LabMaestro_icon :align: left :scale: 30% LabMaestro icon - To turn on the PROPixx screen, click on the 'Wake All PROPixx' button found on the menu on top of the LabMaestro platform .. figure:: figures/meg-operationprotocol/Propixx_awake.png :alt: LabMaestro Platform :align: center :scale: 50% LabMaestro Platform - Or use **VPutil** - Open 'VPutil' - Run `ppx a` and `Enter`, - Check if the screen inside the MSR is on, if the screen is off then: - run `ppx s`, then run `reset`, then wait for a minute, run `ppx a` - Ensure the orientation (vertical flip) of the screen inside the MSR is correct, if not: - Open `LabMaestro`, - On the left of the platform, choose PROPixx from the menu - Check `Rear Projection` box .. figure:: figures/meg-operationprotocol/LabMaestro_rear_projection.png :alt: Incorrect screen orientation fix :align: center :scale: 50% Incorrect screen orientation fix #. Verify your experiment script: - If using `PsychToolBox`: - Open MATLAB (2022b) - Access your experiment `.m` script and launch it - Make sure you arrive to the `Introduction Page` mentioned in the :ref:`design_experiment` section. This is to ensure MEG data recording can be started before the experiment begins - You can do a quick test run to make sure that trigger signals are appearing correctly on the `MEG160` software .. warning:: For a real participant, make sure to turn off the Wifi on the `Stimulus Computer` so that the experiment is not interrupted by an update or other notification from the internet. #. Response Device - Button box: make sure all the optical cables form the button boxes are plugged in correctly as shown in the picture .. figure:: figures/meg-operationprotocol/Left_Response_Button_Box.jpeg :scale: 50% :alt: Left Button Box :align: center Left response box .. figure:: figures/meg-operationprotocol/Right_Response_Button_Box.jpeg :scale: 50% :alt: Projection Mode :align: center Right response box .. figure:: figures/meg-operationprotocol/response_plugs.jpg :scale: 30% :alt: Projection Mode :align: center Plugging the response box: Top row is the `right` response box, bottom row is the `left response box`. #. Microphone inside MSR: - Make sure the sound box is switched on - located under the Stimulus computer - if not click on the green round button - Check if you can hear the participant through the speakers, talking from inside the MSR to the microphone attached to the dewar .. figure:: figures/meg-operationprotocol/Microphone_inside.jpg :alt: Participant microphone :align: center :scale: 50% Participant microphone #. Earplugs - Check the earplugs and make sure the participant can hear you .. figure:: figures/meg-operationprotocol/Earplugs.jpg :alt: Earphones with foam earplugs :align: center :scale: 20% Earphones with foam earplugs #. Prepare the `FastScan` computer: - If the `FastScan` computer is not turned on: - make sure that FastScan device is off (the flat black box next to the monitor, picture below) - turn on the computer then launch `FastScanII` program - turn on the FastScan device .. figure:: figures/meg-operationprotocol/fast_scan_device.png :alt: Fast Scan device :align: center Fast Scan device #. Turn-off the doorbell ring at the entrance of the lab by turning off the plug [IMAGE] .. figure:: figures/meg-operationprotocol/doorbell.png :alt: Doorbell :align: center :scale: 40% Deactivate the doorbell by pressing the plug button. Perform the MEG Experiment (Participant is present) --------------------------------------------------- #. If the participant is a veil-wearing female: - place sign on door - block door with the isolation screen found behind the laser scan room door #. Welcoming the participant and providing them with explanations - [WELCOME] Thank you for joining our study. Is this your first time in the MEG? - [GENERAL OVERVIEW] No worry, Let me explain to you now what we are going to do today. - [BEFORE MEG - HEAD SHAPE] Before you are going into the MEG, we need to do some preparation. - Explain the FastScan head laser scan: - I will scan your head shape with a laser gun [show the FastScan] - This is giving us a 3D reconstruction of the shape of your head - To do that, you need to sit there and not move for around 5-7 minutes - Moreover, I have to mark five points on your forehead and close to your ears with this [show it] washable ink, - it will disappear after just one shower [show the phantom head with the points] - Why are we doing that? To know where your head is located while you are in the MEG. - This is important for the study we are running because we need to know where the data recorded by the MEG sensors - that measure the tiny changes in the magnetic field generated by the brain activity, is coming from. - You know, different people have different head shape/size,... - and they place the head in slightly different sites relative to the MEG sensors. - Why the points? When we are in the MEG room - I will tape you small things called ‘head position coils’ in the places you have these painted points - and this will tell us where your head is relative to the MEG sensors - It looks a bit weird at the beginning, but you get used to it soon(I did the experiment on myself) - [BEFORE MEG - CLOTHES] - Another important thing is that you cannot go inside of the MEG room with any kind of metallic object - because it will create an artifact on the MEG sensors. - To ensure that, I have to ask you to wear this MEG compatible clothes (like the ones in the hospitals). - Please, if you feel comfortable with that, you should take off your bra (most of the time there are small metallic trips or parts). - [INSIDE MEG] - Explain the study-specific instructions here or give them an instruction manual to read.\ - Now, let me recap what we will do today. You need to fill the forms, scan your brain shape, - then you need to change clothes. You go to the MEG room, we tape coils in your forehead. And then, you will do the tasks. - [END OF EXPLANATION] Is everything clear? Do you have any questions? Do you feel comfortable? Are you ok? Please let me know, this is important for us that you understand everything. #. Fill up forms - Ensure that we have the electronically signed all consents and any forms needed specifically for your experiment, or allow them to fill in/sign by hand at the time of the session #. Check up MEG incompatibilities - Participants **MUST** change from their street clothes into scrubs provided clothing. Underwear without any metal and socks can be kept on. Bras should be removed. - Make sure they have NO metallic objects in the body/eyes - Confirm that they do not have: - Surgical clips, artificial heart valve, implanted drug pump - Bullet - Cochlear implant or hearing aid - Dental Retainers or braces - Make-up, especially red color makeup - Hair pins - Jewelry and piercings - Keys - Phone - If the subject arrives with make-up, ask them to completely remove it - If the subject wears glasses, ask them to remove the glasses and provide them with an MR compatible glasses from the briefcase found in the lab - Determine their vision prescription and provide them with the closest matching pair of glasses from the briefcase. - available lens strengths for vision correction -6 to +6 in 0.5 increments .. figure:: figures/meg-operationprotocol/glasses_case.png :alt: Glasses briefcase :align: center MR safe glasses briefcase. - Ask the participant to put their phone on Airplane mode - Put your own phone and all other phones in the MEG lab on airplane mode - Call the security guard on `85849` and ask them to turn off their walkie-talkies for the duration of the experiment .. figure:: figures/meg-operationprotocol/phone.png :alt: Phone :align: center :scale: 50% Phone in MEG lab with a label of security guard office. #. Perform the FastScan laser head scan - Capping the participant - Put a swimming cap on the head of the participant - Make sure the cap is as smooth as possible on the participant's head - Participants with long hair, can keep most part of their hair outside the cap behind their ears and onto the back - The ears must be clear of hair - The cap must cover all the hair that can be seen at the anterior, left and right parts of the head - Smoothen the hair under the cap as much as possible, excess long hair can be drawn to outside the cap at the cerebellum level - The goal is that the cap takes the shape of the skull at best - Mark the fiducials - there are a total of 8 - Use the “T” template, with the line aligning the participant’s nasion as in the below picture .. figure:: figures/meg-operationprotocol/Marker_guide_template.png :alt: Template and Nasion :align: center "T" template on the left and nasion/pre(auricular) positions on the right - Mark the nasion using a pen (fiducial 1) - Adjust the fold in the "T" template to the participants nasion - Using a pen marker, mark fiducials 6, 7 and 8 by using the three holes in the "T" template .. figure:: figures/meg-operationprotocol/fiducials.png :alt: Fiducials :align: center Fiducials numbered by the order they should be laser scanned with. - Mark the the right and left tragi and left and right pre-auricular regions (1cm anterior to the tragi) - (points 2, 3, 4,and 5) - Place a tissue on the neck brace over the area closest to the mouth for sanitary purposes - see picture - Put on the neck brace .. figure:: figures/meg-operationprotocol/neckbrace.png :alt: Neck brace with tissue for sanitary purposes :align: center Neck brace with tissue for sanitary purposes - Perform laser scan - Once FastScan is finished initializing (indicated at the bottom of the software UI): - Open `FastScan II` software on the computer - Press 'New' - Ensure the scanner is in Sweep mode (add [IMAGE]) - Ask the participant to close their eyes and avoid any movements until scan is finished - Point the laser gun at the `laser scanner reference receiver` (the box on the ring you place around the neck, see below) with a half-click, followed by a full click. .. figure:: figures/meg-operationprotocol/reference_point.png :alt: Reference point :align: center :scale: 50% Laser scanner reference receiver .. figure:: figures/meg-operationprotocol/neck_brace.png :alt: Neck brace with tissue for sanitary purposes :align: center Neck brace with laser scanner reference point on the bottom left .. warning:: ** Error message during scanning ** If the following error message appear, this means that the laser scan device lost the reference point. .. figure:: figures/meg-operationprotocol/error_laser_scanner.png :alt: LaserScan error when device is de-referenced :align: center :scale: 50% LaserScan error when device is de-referenced Do not press `Cancel` on the message - point the laser scanner to the reference receiver, first with a half click to point and then a full click. - Scan head shape (sweeps) with full click. Tips: - Include ALL cap surfaces + surfaces with fiducial points - Avoid overlapping sweeps - Making sweeps for head and face separately - Keep a consistent distance between the head and scanner throughout the scan .. hint:: Press half a click while using the laser scanner to shift the view on the `FastScan II` software to the current view as seen from the device. This feature allows you to quickly identify areas that are not covered well by the current laser scan. - After sweeps, switch to Laser Points and click on Stylus List for points options, ensure that Stylus > Properties > Capture Points (NOT capture lines) - Start registering the fiducial points following this order - see picture. -The 8 points are as follows: 1. Nasion - between eye-brows at the nasal bridge 2. Left tragus - cartilage of left ear (not marked) 3. Right tragus - cartilage of right ear (not marked) 4. Left marker - pre-auricular marking left ear 5. Right marker - pre-auricular marking right ear 6. Center forehead - center forehead marking 7. Left forehead - left forehead marking 8. Right forehead - right forehead marking - Ensure that you have only 8 points selected on the Stylus List - Tell participant they can move back again - Return the scanner and box to the foam holder on the table, and make sure none of the cords are on the floor `THIS IS A VERY EXPENSIVE DEVICE` - see picture .. figure:: figures/meg-operationprotocol/fast_scan_pack.png :alt: Fast Scanner Box :align: center FastScan should ALWAYS be placed like this: laser on foam, cables on table (not floor). - Remove the cap from the participant's head and toss into the washing bin - Remove the neck brace - Files must be saved amd stored according to BIDS protocol format - Please refer to `Data Naming and Storing: MEG `_ #. Participant goes into the MSR - Participant should remove shoes - Subject sits on the bed facing the researcher - Place the five Head Position Indicator (HPI) coils on the marker points - Each HPI coil is marked by a color that corresponds to the position of placement of the coil on the head - Bring the forehead markers over the top of the head so the wires are not in the participant’s face - The position of the HPI coil on the participant's head should follow the following mapping: .. figure:: figures/meg-operationprotocol/Marker-placement.png :alt: Colour coded marker placement :align: center :scale: 30% Position of Marker Coils also called Head Position Indicator (HPI) coils - As a note, the red and yellow markers should be placed in anterior to the tragus at marked points 4 and 5 - Place earphones - Assist the participant with the wires while they move into the helmet - Place the pink pillow under the participant's legs for the back support - If the experiment requires it, place the `Vpixx Response Box` or the `Dial` in their right/or left hand depending on experimental design - Optionally tape the box to the mattress, to avoid the box falling - Tape any loose wires for the markers and the button boxes - **Ensure that the participant is comfortable** - Close and lock the MSR door .. figure:: figures/meg-operationprotocol/hpi_coils.png :alt: hpi coils :align: center HPI Coils placement on head. - Communicate with the participant - Turn on the microphone - Talk to the participant through the Vpixx microphone - Make sure the participant is replying back and that the voice quality is good - Tell them that the experiment is about to start and that they should refrain from any movement - Tell them that if they need to speak to you for any urgent issue, they can do this freely at any time - Turn off the microphone #. Run experiment and recording - Run your script until it lands on the `Introduction Page` of your script as explained in the :ref:`design_experiment` section. - Prepare MEG recording #. Prepare MEG recording - On ‘MEG MAIN PC’ computer, open MEG Lab (on desktop), aka MEG160 - The participant is now in the MSR, door is CLOSED, the lights have been switched off and the Brightness dial has been turned to the minimum - If empty room data has not been acquired prior to the current experiment, Auto Tuning should be performed -Menu -> Acquire -> Auto Tuning -> Ok - Wait for the auto-tuning to be done - This should be followed by a Sensor Check - From Menu -> Acquire -> MEG Measurement -> Monitor and Acquisition window should open - In the 'Sensor Control' window ensure or set these parameters - HPF to `0.1 Hz` - LPF to `500 Hz` - BEF to `THRU` - Click on 'Sensor Check' - Let the Sensor Check run for around 30 seconds - Uncheck 'Sensor Check' - Make sure that the sensor display identical sinusoidal wave - Remember that `Sensor 91` is broken and will not display a sine wave - File storage location and naming convention - From the menu “Acquire (Q)”, select “MEG Measurement (Q)” - On “Monitor and Acquisition” window > ‘Data Acquisition’ - Patient ID: sub- [e.g., sub-001] - Patient Name: sub-_ses-_task- [e.g., sub-001_ses-01_task-resting-state] - Foldername: D:\\MEGDATA\\\\STUDY_CODE\\sub- - “Lock” [only if MSR door is CLOSED] - Wait until MEG sensors are stable i.e. no upward or downward trend - Perform marker measurement - Switch off microphone - On “Monitor and Acquisition” window: - Marker measurement > Start > OK - see picture - When done, column ‘GOF%’ should be around 99% - If not, at least one of the head coils is misplaced - If at least 3 head marker coils are in place - PROCEED - Click OK .. figure:: figures/meg-operationprotocol/daq_measurement.png :alt: Daq measurement :align: center Continuous mode (left) and Marker measurement (right). - A `.mrk` file named as `YYYYMMDD-x.mrk` is automatically generated in the specified directory following the marker measurement, where `x` is an integer 1,2,3,... indicating the order of recording of the marker - If your experiment is lengthy i.e. 2 hours long, we recommend that you perform a marker measurement in between, i.e., after 1 hour is elapsed - On “Monitor and Acquisition” window: - Set/Ensure that: - HPF: `0.1 Hz` - LPF: `500Hz` - BEF: `THRU` - Continuous Mode > Start - see above picture - Sampling rate: 1000 (default) - Time: 4000 [66 minutes] (this is the maximum possible time in the MEG160 software) - Start Acquisition - At this point, you can safely start your experiment from the `Stimulus computer` - If your experiment is lengthy, we recommend that you perform a marker measurement in between runs - A marker measurement must be performed at the end of an experiment #. Stop continuous recording (when task finishes, or if the experiment spans for more than 4000 seconds and needs a new recording) - On “Monitor and Acquisition” window - see picture 14: - Continuous Mode > Abort #. Finish up the MEG session (when all tasks are done!) - On “Monitor and Acquisition” window: - ‘Unlock’ [VERY IMPORTANT STEP, DO NOT OPEN THE DOOR BEFORE IT] - Close MEG160 software #. Take out participant from MSR - [ONLY WHEN SENSORS ARE UNLOCK!] Open the MSR door - When removing the head-position indicator coils and earphones, do the removal yourself. The coils in particular are very fragile and expensive. Remove with care. - Ask participant to change clothes back and put the scrubs in the wash bin (in the laser scan room) After the MEG session --------------------- #. Settings MEG - Do not shut down any of the computers. They can all be locked or logged off. - Turn on the heater cable [THIS IS VERY IMPORTANT] - see picture above - Turn off the MSR lights. - Double-check that you turned the heater back on. #. Clean room - Remove linen and place in bin - Clean the helmet, head-position indicator coils, and button box with wipes. - Wipe down the FastScan neck brace and any other surfaces the participant came in contact with #. Postprocessing - Apply Noise Reduction filter using the reference magnetometers - The KIT system is equipped with reference magnetometers on channels 208 till 223, that measures the external magnetic field - [Optional] you can noise reduce your SQUID data (channel 0-207) by applying a filter that uses the data from channels 208 to 223 - Open the produced `.con` file in the default app `MEG160` then apply a Noise Reduction filter using Edit -> Noise Reduction - Make sure the Magnetometers on channels 208, 209, 210 are used. - Execute the noise reduction, then File -> Save As -> add `_NR` at the end of the file name. - Transfer both files to NYU BOX as detailed in the data uploading section. - FastScan Instructions - Open FastScanII software (icon on desktop) - Please refer to `MEG-Laserscan files `_ - To delete points you’ve selected, simply click on the backspace key on your keyboard - Then go to Edit > Generate Surface - Smoothing = 5mm - Decimation = 3mm - In the pop-up, click on Apply Basic Surface, then close it - To save your head scan, please refer to `MEG-Laserscan files `_ - Edit > Generate surface > Apply basic surface - Basic surface has fewer than 10,000 points - If not, decimate: Generate > Surface Simplification = 0.10 > Apply (Basic Surface) - File > Export > save as Please refer to `MEG-Laserscan files `_ #. Uploading to NYU BOX - You should have your own folder on `NYU BOX` named after your project - Refer to the `Data Uploading `_ section to upload your data Appendix. A: Stylus location and markers ---------------------------------------- .. image:: ../graphic/markers1.jpeg :width: 400 :alt: AI generated MEG-system image .. image:: ../graphic/markers2.jpeg :width: 400 :alt: AI generated MEG-system image The following table is a summary of the position of each registered stylus location and whether or not a KIT coil will be placed on that position. +-------+---------------------+--------------------------------------+ | Index | Body Part | Marker Coil Information | +=======+=====================+======================================+ | 1 | Nasion | KIT: NO, OPM: | +-------+---------------------+--------------------------------------+ | 2 | Left Tragus | KIT: NO, OPM: | +-------+---------------------+--------------------------------------+ | 3 | Right Tragus | KIT: NO, OPM: | +-------+---------------------+--------------------------------------+ | 4 | Left Pre-Auricular | KIT: YES, OPM: | +-------+---------------------+--------------------------------------+ | 5 | Right Pre-Auricular | KIT: YES, OPM: | +-------+---------------------+--------------------------------------+ | 6 | Center Forehead | KIT: YES, OPM: | +-------+---------------------+--------------------------------------+ | 7 | Left Forehead | KIT: YES, OPM: | +-------+---------------------+--------------------------------------+ | 8 | Right Forehead | KIT: YES, OPM: | +-------+---------------------+--------------------------------------+ Appendix. B: Marker coils for KIT order of appearence in .mrk ------------------------------------------------------------- The registered `.mrk` file containing the position of the HPI coils for KIT. Using `fieldtrip` function named `ft_read_headshape('PATH TO .mrk')`, we report the order of appearence of the HPI coils positions in the `.mrk` file below. This has been tested with many `.mrk` files in the current pluggin setting (last column) +----------------------+-----------------------------+-------+---------------------+ | Order of appearance | Placing position of HPI | Color | Plugging order | | in the .mrk | Coil on head | | in Marker Box | +======================+=============================+=======+=====================+ | 1 | Central Forehead (CF) | Blue | 2 | +----------------------+-----------------------------+-------+---------------------+ | 2 | Left Pre-Auricular (LE) | Red | 0 | +----------------------+-----------------------------+-------+---------------------+ | 3 | Right Pre-Auricular (RE) | Yellow| 1 | +----------------------+-----------------------------+-------+---------------------+ | 4 | Left Forehead (LF) | White | 3 | +----------------------+-----------------------------+-------+---------------------+ | 5 | Right Forehead (RF) | Black | 4 | +----------------------+-----------------------------+-------+---------------------+