template image and the functional template is further registered
to a standard brain atlas. In the latter, the functional-to-anatomical
registration is done in each subject’s coordinate system and
the intersubject or subject-to-atlas registration is done for the
high-resolution anatomical images [Fig. 1(c)].
In almost all functional localization procedures, except in
some of those applied to neurosurgery, a final step consisting
of activation labeling is required. Usually, this step involves a
nonrigid registration to a standard digital brain atlas. By reporting
the results in a standard labeling framework, different
studies can be compared. A digital brain atlas consists of a typical
high-resolution brain structure with anatomical labels, coordinate
labels, and sometimes functional labels [1], [3]. For group
analyses, a brain template (e.g., the target brain) is registered to
the brain atlas prior to functional localization, and a simple 3–D
overlay to the atlas space is done for activation labeling. The accuracy
and reliability of activation labeling is determined by the
accuracy of registration between the different subjects and the
template or the atlas, or between the template and the atlas.