Fig 1. Creation of the Brain-Grid.

A) The first step during the creation of the Brain-Grid is illustrated on the sagittal or axial slices: The anterior insular point (the most anterior landmark of the insular sulcus) is identified on both sides and the first line is drawn on the sagittal plane (MNI: Y 28, Talairach: Y25). The second line (drawn as well on the sagittal plane) is parallel to the previous one, crossing the posterior insular point (MNI: Y-23; Talairach: Y-24). On the midline (with sagittal view) the point where the calcarine fissure (V1) meets the most anterior portion of the parieto-occipital sulcus should be identified in order to track the third parallel line on the sagittal plane (MNI: Y-68; Talairach: Y-66). The same line crosses the temporo-occipital junction between the posterior portion of the fusiform gyrus and the inferior occipital sulcus more basally on the axial plane. The 3 lines on the sagittal plane will segment the whole brain into 4 grid voxels. The S1 voxel is the pre-insular/prefrontal portion of both hemispheres. The S2 is enclosed within the anterior insular point and posterior insular point (landmark for the second sagittal line). The S3 includes the retro-insular region and the parietal lobe, and the S4 includes primarily the occipital lobe and the border with the parieto-occipital sulcus. B) The second step during the creation of the Brain-Grid system is the identification of the right slice on the coronal plane (Into the MNI space: Y-5; Talairach Y -7). The first of the 2 parallel lines crosses the inferior insular point (the lowest limit of the insular sulcus) and the floor of the third ventricle that leads to the rounded shape of the mammillary bodies. In most patients, this horizontal line usually crosses the superior temporal sulcus on both sides (MNI: X0, Y-5, Z-13; Talairach: X0, Y-7, Z-7). The second line passes through the cistern/space between the cingular gyrus and the callosal body in the midline (MNI:X0, Y-5, Z33; Talairach: X0, Y-4, Z 31). C) Third step: Once the coronal segments and the sagittal segments are created, one should identify the middle frontal sulcus bilaterally, which is easily recognizable on the axial slice that shows the level of the lateral ventricle on the coronal reference (shown on the side). The 2 lines should be parallel to the midline, connecting this sulcus with the middle occipital gyrus crossing the white matter of the external capsule without invading the periventricular ependyma (right line, MNI: X33; Talairach: X32. left line, MNI:X-33; Talairach: X-32). The third and last line follows the midline along the falx and/or the septum pellucidum (MNI: X0; Talairach: X0). In this way 4 longitudinal segments are created, termed A1 to A4, from the right lateral side to the left lateral side.