MEG

HPI Placement

MEG alone:

HPI coils should be applied directly on the scalp surface using both double-sided rings and micropore tape (no paste!). They should be positioned as far as possible from each other at 4 specific locations on the head:

* one on the left(right) mastoid, i.e. slightly behind and above each ear right below the hairline.
* one on the left(right) forehead right below the hairline.

Figure: Placement of HPI coils (gray wires). (Pictures borrowed from here).

IMPORTANT:

  • All coils should be positioned high enough to ensure that they will be inside the dewar once the subject is in the MSR.
  • The locations of the four coils should NOT form a perfect square, i.e. distances between them should be all slightly different (a perfect square configuration might cause problems in head position reconstruction).

Simultaneous MEG/EEG :

In this case HPI coils will be placed on the EEG cap rather than on the skin, as follows:

  • Two in front of the head (plastic cables) and two in a more posterior position (parietal regions). Use double-sided rings and scotchtape to fix them on the EEG cap. As with MEG alone, place them high enough and ensure some asymmetry in coil locations (see above).

Figure: Placement of HPI coils (gray wires) on EEG cap. (Pictures borrowed from here).

Important tips:

  • Scotchtape the cables of your HPI coils on the right shoulder of your subject. Be careful to let enough cable length for the subject to move her/his head.
  • It is very important to well fix HPI coils: they should not move during ALL the time of your recording.