External landmark and head-shape-based functional data normalization

Functional data, as obtained from magnetoencephalography (MEG) techniques, is frequently transformed to a template brain space for pooling data across the population. This transformation is often performed via an intermediate magnetic resonance image (MRI) of the subject's brain that is first registered to the template brain MRI. However, in many instances, it is difficult, expensive or undesirable to acquire MRIs, and since reconstructed functional data is lower resolution, the full information in MRIs is not required for registration. We present here two alternative options for computing the transformation of functional data to a common template space. These alternatives compute the registration based on external landmarks placed on the head, and the external shape of the head, features that are considerably simpler and inexpensive to acquire than MRIs. We present quantification of the accuracy of using these alternative features for registration, and show that they give accuracy for functional data registration that is sufficient given the functional data resolution, and is comparable to existing methods that are commonly used.