Download Appendix: Fiber Tracking Methods The cerebral peduncular fibers

Appendix: Fiber Tracking Methods
The cerebral peduncular fibers (CPF) were reconstructed into projections to the anterior frontal,
superior frontal, parietal, and occipital lobes. The first ROI for all regions was drawn on an axial
slice passing the upper boundary of the midbrain to enclose the cerebral peduncle. Subsequently,
a second ROI was drawn for each CPF region using the ROI operation AND to retain fibers
going through the two ROIs. For the anterior frontal projections, the second ROI was placed on
a coronal slice one slice anterior to the corpus callsum (CC). The second ROI for superior
frontal was selected as the most inferior axial slice showing the separation of superior frontal
projections from parietal projections by the central sulcus. This slice was also used for tracking
the anterior parietal projections. For the posterior parietal projections, the second ROI was
drawn on a coronal slice midway between the posterior boundary of the CC and parietal-occipital
sulcus. The same coronal slice was used for tracking the occipital projections.
The cerebellar peduncles (CP) were reconstructed separately as inferior (ICP), middle (MCP),
and superior (SCP) CP. Firstly, the cerebral peduncle was drawn on an axial slice to find the
characteristic dip of the CP on the midsagittal slice. The coronal slice was then set at the dip and
the 1st ROI for the CP drawn to enclose the entire cerebellum. For reconstructing the ICP, the
second ROI was drawn on an axial slice passing the lower boundary of the pons where the ICP
was separated from the remaining fibers, and the ROI operation AND was applied. The MCP
and SCP were reconstructed similarly by setting the coronal slice at the posterior boundary of the
pons for the MCP and by setting the axial slice at the upper boundary of the pons for the SCP.
The extreme capsule (EC) fibers were tracked according to four functionally distinct regions
consisting of the anterior medial region (projecting to the prefrontal lobe), the posterior medial
region (projecting to the sensory-motor area), the anterior lateral region (projecting to the frontal
operculum), and the posterior lateral region (projecting to the temporal lobe). The EC fibers
were drawn on three axial slices that were three, six, and nine slices, respectively, inferior to the
fornix crus, in order to enclose the entire EC. Any fibers crossing between the hemispheres and
into the internal capsule, thalamus, basal ganglion and occipital lobe were deleted. Next, for the
anterior portion of the EC anterior medial projections, the coronal slice showing the separation
between anterior medial and anterior lateral projections was chosen for drawing the second ROI
using the AND operation. For the superior portion of EC anterior medial and posterior medial
projections, an axial slice above the EC posterior lateral projections was chosen and the
precentral sulcus used to demarcate the EC anterior medial and posterior medial. The posterior
portion of the EC posterior medial projections was selected on the coronal slice posterior to the
EC posterior lateral projections. For lateral EC projections, sagittal slices were utilized for
drawing the second ROIs. For the anterior lateral projections, the second most medial slice
showing the separation of anterior lateral projections from the remaining EC fibers was selected,
and for the posterior lateral projections, the most medial slice where the posterior lateral
projections formed a distinct fiber bundle was used. For each region, fibers straying into other
EC fiber regions were removed.
For reconstructing the cingulum bundle (CB), three coronal slices were utilized, with the first
being at the inner curve of the CC, the second at the posterior CC, and the third, midway
between the first two slices. The complete CB was tracked by drawing the CB and its branches
on the first two slices using the ROI OR operation, and on the third slice using the AND
operation. To track anterior and posterior CB, the first ROI was placed on the third ROI slice
and the second ROI on the first ROI slice for anterior CB and second ROI slice for posterior CB
using the CUT operation.
Only the body of the fornix (FB) was reconstructed because the body, not crus, provides
measurements with high inter-rater and test-retest reliability (Wang et al., submitted). The two
ROI slices were chosen as the most inferior axial slice showing the FB, and the most posterior
coronal slice where the fornix remained as one bundle. The ROI operation was CUT.
The angular bundle (AB) was reconstructed by first finding the coronal slice midway between
the slice anterior to the temporal stem and the middle of the CC splenium. Subsequently, ROIs
were placed on two coronal slices five slices anterior and five slices posterior to the initial slice
using the OR operation. The third ROI was drawn on the middle slice using the AND operation.
The arcuate fasciculus (AF) was tracked separately into anterior, posterior, and direct AF (Catani
et al., 2005) with anterior AF connecting Broca’s area and the supramarginal gyrus, posterior AF
connecting Wernicke’s area and the supramarginal gyrus, and direct AF linking Broca’s area
with Wernicke’s area. A sagittal slice lateral to the anterior AF main body was chosen for
tracking the AF. Since not all fiber regions were reconstructed for the participants because of
individual variability in this fiber tract, the three regions were combined to form AF complex.
The left direction AF and right anterior AF were retained because they were reconstructed from
all and 74/75 participants, respectively.
For the remaining association fibers, the coronal slice anterior to the temporal stem was selected
for tracking the uncinate fasciculus. The AND operation was applied to select fibers appearing
in both the temporal and frontal lobes. For tracking the inferior longitudinal fasciculus (ILF),
two coronal slices were utilized, with the first slice being set to the posterior boundary of the CB
and the second slice midway between the slice anterior to the temporal stem and the first slice.
The ROI operation AND was utilized. The result was then inspected to delete the inferior
frontooccipital fasciculus (IFO) and CC fibers using the NOT operation. For reconstructing the
IFO, the same first slice of the ILF was utilized. The second ROI was placed on the coronal slice
anterior to the temporal stem using the AND operation.
Finally for reconstructing the CC, two sagittal slices 4 mm from the midsagittal slice were
chosen and the AND operation applied. Since the older participants showed substantial amounts
of fiber projecting inferiorly and laterally, such fibers were removed from all participants. In
addition, fibers from the CC splenium that overlapped with the IFO were also deleted. The CC
was subsequently parcellated into four regions with equal width by placing rectangular ROIs on
the midsagittal slice using the AND operation.