We now have small inflatable bags (repurposed disposable neonatal blood pressure cuffs), that we can stick inside the MEG helmet to help reduce head movement. The idea is to have one on each side, above and slightly in front of the “ear notches” inside the MEG helmet, with the tubes hanging down in front of the ears.
Placing/removing: The cushions have a small velcro patch on one side. We stick reusable silicone tape on it and press it against the inside of the helmet. To remove them, first gently peel off the cushion, which will leave the tape in the helmet. Then pull on a corner of the sticky tape, pulling gradually in a lengthwise direction, such that the tape stretches and pulls off. We can replace the tape if it breaks, but it is reusable (even washable).
I suggest we keep them hanging in the helmet generally, but they can be removed as needed, e.g. when the head doesn’t fit well or when using an EEG cap. We should wipe them as well when cleaning the helmet.
They should not be placed at the back of the helmet, such that the participant rests against them, as there would be a risk of it deflating and causing a slow position drift. For padding at the back (mostly when lying down), we can keep using foam, bubble wrap or small towels.
Using them is fairly simple. There is a big syringe used to push air in, and two stopcocks (valves) which allows to open everything (left picture) or close everything (right picture). Note that these work opposite to ball valves: the handle is the “closed” side, while the 3 other sides with small arrows indicate “open” directions.
To fill: set the valves to the open position, fill the syringe with air, put a finger on the small open tube, and push the syringe plunger gradually, checking with the participant when they start feeling some pressure. If they say it’s too much, just lift your finger a fraction of a second to let some air out. Otherwise, just close the valves and double check the comfort.
Importantly, we do not want to make the participant uncomfortable, but mostly reduce the available space at the sides and front of the head. Filling the cushions “not enough” is better than “too much”.
To empty: set both valves to the open position. That’s it! Best to do this before lowering the chair. Leave them open for the next user.