Checking for head positions between runs
Since MEG sensors are obviously not attached to the participant head, MEG measurements might be affected by distorsions induced by the fact that, even if instructed to stand perfectly still, people moves a little bit during eperiment. Despite any practical expedient to avoid head movements during recordings, some residual displacement accross different recording blocks tipically remains in MEG data.
At a very first step of analisys you have to evaluate the extent of these displacements. You can hen choose between different strategies to deal with: realining data in sensor space using MaxFilter (see Cleaning and realigning data using MaxFilter) or in soource space by mean of anatomy co-registration.
In any of these case we provided a tool running on meg-servers and Minea to help you in inspecting residual head displacements and to choose a suitable reference for Maxwell Filtering sensor space realignment. A description of the tool can be found on this slides: Extract HeadPositionHistory.
For further information about this topic you can ask the MEG core team for a consultancy.