Computational protocol: Large-scale functional networks connect differently for processing words and symbol strings

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Protocol publication

[…] Significant coherence modulations at the level of the cortical grid were visualized on the cortical surface of an atlas brain using FreeSurfer. For visualization of the connections we used a circular plotting scheme [] in which the nodes were based on an anatomical parcellation (AAL, ; []). For this purpose, we transformed the coordinates of the individual subjects to MNI (Montreal Neurological Institute) coordinates. MNI coordinates were obtained by combining the linear transformations between the head and Freesurfer MRI coordinates (6-parameter rigid body, obtained from the Elekta Neuromag software) and between the FreeSurfer MRI of an atlas brain (MNI306) to MNI coordinates (12-parameter affine, obtained from FreeSurfer) []. The data were represented by a reduced adjacency matrix C, which was constructed by assigning an anatomical label to the connection start and end point, such that the value of matrix element C(i,j) corresponded to the number of significant connections between anatomical areas i and j.To quantify the lateralization of the networks we calculated a lateralization index LI for the number of connections within each hemisphere separately for words and symbols: LI = (left—right) / (left + right). The cut points LI>0.2 and <0.2 (i.e. at least 50% more results were found in one hemisphere than in the other) were considered to indicate left and right laterality, in concordance with previous studies []. […]

Pipeline specifications

Software tools FreeSurfer, AAL
Application Magnetic resonance imaging
Organisms Homo sapiens