🖊️Chapter 4: Polhemus

1. Seat participant in Polhemus chair.

   • The cube is still adjusted correctly

   • The participant is centered on the chair

   • The participant is in a comfortable position

   • The participant can sit still in this position

2. Apply the Nasion Sensor. Uncoil the Nasion Sensor from the rack. Secure the Sensor under the nasion bracket of the EEG net. Keep the sensor as straight as possible.

3. Open BrainStorm.

   

   On the Polhemus computer, locate and double-click the BrainStorm icon at the centre of the Desktop. This will open the MATLAB script for BrainStorm.

   

   In the Editor panel, click on ▶ Run. This will open BrainStorm's user interface.

4. Start Digitizer. Navigate to File > Digitze. This will open the digitizer window. Enter the participant's ID. BrainStorm will then allow you to start digitizing.

5. Wield the Stylus. Uncoil the stylus from the rack, and hold it in your preferred hand. The stylus will be used to collect the position of each electrode, as well as the subject's ears & nasion: L-EAR + R-EAR + NASION = 3 fiducials 👂👃 64 EEG + REF & COM = 66 electrodes ⛑️ = 69 positions 👀 The stylus has a cap concealing its needle-like tip. Keep the cap on until Step 8. DO NOT PROCEED TO THE NEXT STEP WITH THE CAP OFF

6. Collect Anatomical 3 Fiducials. Anatomical fiducials are physical landmarks that allow us to build a head model. Examples of fiducial include eyes, ears, nose, etc. The Polhemus only needs the ears and the nasion to do this accurately. While collecting these positions, the cap covering the must remain on. To collect a fiducial:

   • Hold the tip of the pen (with cap) to the point of interest.

   • Once steady, tap the stylus button very briefly. ⚠️ A quick tap on the button will suffice! Holding it to long will collect the same position for multiple electrodes.

   • Hold the stylus in that position until you hear the confirmation tone. ⚠️ Avoid pulling away immediately after tapping the button. Wait until the confirmation tone has played.

   • The order of the fiducials is collected as: L-EAR + R-EAR + NASION. Once collected, Polhemus will build a head model for the subject.

7. Collect 66 Electrode Positions.

   Remove the protective cap to reveal the sharp tip of the pen. To collect an electrode position:

   • When collecting an electrode position, hold the tip of the pen to the metal contact on the electrode surface.

   • Once steady, tap the stylus button very briefly. ⚠️ A quick tap on the button will suffice! Holding it to long will collect the same position for multiple electrodes.

   • Hold the stylus in that position until you hear the confirmation tone. ⚠️ Avoid pulling away immediately after tapping the button. Wait until the confirmation tone has played.

   • The order of the electrodes is collected as: EEG01-64 + REF . DO NOT FORGET TO COLLECT REF as a non-EEG electrode.

8. Save the subject's head model. Once all positions have been collected, save the subject's head model (.pos file) under their subject ID.