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. Author manuscript; available in PMC: 2011 Feb 15.
Published in final edited form as: Neuroimage. 2009 Nov 14;49(4):3075. doi: 10.1016/j.neuroimage.2009.11.018

Figure 1.

Figure 1

Illustration of analytical approaches. A part of normal cortex with curvature is at the top and the same part of the cortex on the spherical model of cortex (spherical cortex) is at the bottom. The small yellow squares are sMRI voxels and the large blue boxes are fMRI voxels. Note that the voxels are transformed in the spherical cortex during the inflation of cortex to sphere. In the Volume-based analysis, A: a fMRI voxel (blue line box) was smoothed to 1 voxel length in 3-D in Euclidean space (blue dash line box), and occupies the active cortical volume (purple shaded). The intersection of the smoothed voxel and a cortical surface is defined as a surface ROI in existing studies (red line) or in the volume-based analysis of the current study (green line). Two surface ROIs are similar if the smoothed voxel occupies the entire cortical depth. B: A fMRI voxel is registered in part of cortical depth, and 3-D smoothing expends the active volume to an adjacent gyrus. The surface ROI is split on both gryi. The current study defined a larger surface ROI (green line) than existing studies (red line). A′: The A is transformed in the spherical cortical model. Previous studies defined active vertices on one depth at surface ROI (red line) and projected the surface ROI to the entire cortex as active volume (red dash box). The new multiple-plane approach defined the active vertices on five planes at 0, 25, 50, 75, and 100% of cortical thickness from white matter border (black lines), and projected the active vertices of each plane to sMRI voxels (yellow) in a ribbon of 12.5% of cortical thickness above and below the plane within cortex (black dash line). Active vertices on all planes are summed on one surface as a surface ROI (green line) for thickness measurement, and hit voxels in all ribbons are assembled together as a volume ROI to estimate the active volume (purple). B′: The B is transformed in the spherical cortical model. The multiple-plane approach defines a larger surface-ROI (green line) than existing studies (red line) because it summed activity on two planes. In contrast, this approach estimates a smaller active volume (purple) than existing studies (red dash line box).