Cleveland Family Study

17.8.3.4 To Determine CZ (Common Ground)

1. Have the participant sit in a chair.
2. Standing at the side of the participant, place the zero line (0) of the tape measure on the marked inion.
3. Holding the tape measure in place with your non-dominant hand, stretch the tape measure upwards, over the crown of the head, until it reaches the marked nasion.
4. Determine the total distance between the inion to nasion, in centimeters. Remember this number (it may help to write it down).
5. Compute 50% of this total measurement (or use your measurement guide).
6. Remove the tape measure, and re-position with the zero line on the marked nasion.
7. Stretching the tape measure upwards, over the crown of the head, mark the value for 50% of the nasion to inion total. When marking these sites, make a large enough line so it can be easily found.
8. Remove the tape measure and stand behind the participant.
9. Place the zero line of the tape measure on the left pre-auricular mark.
10. Stretch the tape measure over the top of the head, and along the mark that has just been made, until it reaches the right pre-auricular mark.
11. Determine the total distance from pre-auricular to pre-auricular in centimeters. Remember this number (it may help to write it down).
12. Compute 50% of this total measurement (or use your measurement guide).
13. While firmly holding the tape measure at the left preauricular mark allow the tape measure to drape over the crown of the head while marking the value for 50% of the total measurement. This mark should intersect the previously made line. The point at which the lines intersect is the site for the Cz electrode placement.