Fig. 4.

Spontaneous slow waves often propagate via the cingulate. For each wave, we calculated a streamline for each origin voxel. (A) The origin voxels (red circles) and streamlines (red tubes) for a single slow wave overlaid on an anatomical MRI. This slow wave originates primarily from right anterior cortex (including the inferior frontal and middle frontal gyri). It propagates medially and posteriorly. (B) Streamlines for an individual subject. Only the longest 10 streamlines for each wave are shown. A dense streamline highway can be seen running along the anterior–posterior axis in the medial portion of the cortex. (C) For each voxel, we calculated the number of waves with streamlines that passed through it. A flat cortical map of the propagation density is shown for each voxel, expressed as a percentage of the total number of waves. Propagation hot spots are seen along the cingulate cortices. (D) Flat cortical maps of the propagation density for each subject. AC, anterior cingulate; CG, cingulate gyrus; INS, insula; PCC, posterior cingulate.