Now we will prepare two areas just underneath the chin. The electrodes placed here will measure muscle tone overnight which helps us determine whether a participant is awake or asleep, and to identify the moments when someone is roused from sleep.

First, measure 2cm beneath the edge of the jawline along the midline of the face, and swab the areas 2cm to the left and right of this point (the green areas in the image).

Once swabbed, abrade with gel for 30 seconds.

*If the participant has facial hair in these areas, prepare the alternate sites at the edge of the hairline at the outside of the upper lip on each side (shown here). However, these sites yield less useful data for our analysis, so consideration should be given to shaving.