Supplementary material
1 Why the average age of the youth control group is ~ 26 years
In 1905, Albert Einstein published four groundbreaking papers in four
different fields: photoelectric effect, Brownian motion, special relativity, and the
equivalence of mass and energy. The year of 1905 has therefore been called
Einstein's miracle year, which took place when he was only 26 years old
(http://en.wikipedia.org/wiki/Annus_Mirabilis_papers). It is remarkable that
Einstein had developed his supranatural intelligence by this young age.
Accordingly, the average age of our young control group was selected to be about
26 years (range from 24 to 30 years), an age by which most people have finished
their college education and the brain has reached its maximize weight (Barber et
al., 1970).
The resolution of MRI data in this study is about 1mm3 due to technological
limitations, so partial volume effect on the callosal edges may exist and the
measured callosal thickness from MRI data of the control brains could therefore
be slightly thicker than the actual thickness. Previous studies illustrate that men
have maximum callosal size or width in their early 20’s, which subsequently
decreases with chronological age (Cowell et al., 1992). On the other hand, the
photos of Einstein’s 76-year-old brain were taken after his brain was preserved
and fresh brain tissues may have shrunk because of their perfusion with 10%
formalin (Aboitiz et al., 1992). Thus, if there are any subregions in which
Einstein’s corpus callosum is thicker than those of the young controls, it is logical
to conclude that those regions in Einstein’s brain were even thicker when he was
26 year old.
2 Subregions of the corpus callosum
Figure A1 The boundaries of anatomical divisions of the corpus callosum were identified at
specified points (ratios) along the line connecting the anterior and posterior end points. As
described in the text, these subdivisions were used to standardize and quantify measurements in
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thickness in various subregions of the corpus callosum.
3 Measurements of Einstein’s callosal dimensions
Fig.1. clearly shows the left and right mid-sagittal callosal cross section in both
hemispheres. Because there is no scale bar on either photograph they cannot be
measured directly. However, the scale/callibration of these photographs can be
determined using hemispheric lengths (17.2 cm left/ 16.4 cm right) reported in
the literature (Anderson and Harvey, 1996). To reduce errors of Einstein’s
corpus callosum measurement caused by rescaling and distortion, the corpus
callosum on the left and right hemispheres were both measured. The maximum
lengths of Einstein’s callosum on both hemispheres are consistent with the
published measurements, so the two photographs have the same scale. The
photograph of the left hemisphere was flipped horizontally in keeping with
medical convention, and then rotated anticlockwise 3.2 degrees to align the
maximum length of the corpus callosum along the horizontal, with the genu on
the left and splenium on the right. The photograph of the right hemisphere was
also rotated to align the maximum length of corpus callosum horizontally.
There is a little breach under the callosal rostrum in both hemispheres (Fig. 1).
The breach on the left hemisphere is ‘M’-shaped and on the right hemisphere is
like a flipped ‘V’. If there was only one breach in Einstein’s corpus callosum, it
would be the same shape on both hemispheres. Additionally, the entire corpus
callosum shows "saw" marks that are probably from the scalpel that was
(presumably) used to separate the two hemispheres, and one of these marks is
seen on the breach of the left corpus callosum. In contrast, all controls’ corpus
callosums were carefully reviewed and no breaches were found. Nor does this
feature appear in previously published pictures of corpus callosum (Park et al.,
2011; Wang et al., 2009) . Hence, it is very likely that the breaches under the
callosal rostrum in both of Einstein’s hemispheres were introduced when the two
hemispheres were separated in 1955. The breaches were therefore ignored when
outlining the callosal contours.
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To measure regional callosal thicknesses/widths in the midsagittal plane, the
contours of both corpus callosums were outlined by one rater (M. W.) using
ImageJ software (National Institutes of Health，http://rsb.info.nih.gov/ij/). The
boundaries of the callosum on both hemispheres were identified by the pixels at
the edge of callosal masks; top and bottom edges were defined according to
anterior and posterior end points. The anterior end points were easy to identify
at the callosal anterior tip, and the posterior end points were estimated
repeatedly to assure that the maximum length of the callosal middle line was
determined. The middle line of a 2D object was defined by
the Symmetry-Curvature Duality Theorem (Leyton, 1987). An approximate
middle line is determined by searching the points on the callosal mask. Briefly,
the points on the middle line have two characteristics, the distance of one point
to the top edge plus the distance of this point to the bottom edge has a minimum
value and the difference between two distances also has a minimum value. The
edges of the top, bottom and middle lines (running rostrocaudally through the
center of the corpus callosum) were redigitized with a b-spline interpolation,
resulting in 400 points per section. According to the characteristics of the middle
line, for every point on the top edge a point exists on the middle line which is the
shortest distance from it. The points on the bottom edge are also determined by
their shortest distances from corresponding points on the middle line. Once the
corresponding points were identified, the distances from the points on the top
edge to their corresponding points on the bottom edge were calculated, and
defined as the thickness of corpus callosum at their respective locations. The
middle points of these segments determined a new line coursing rostrocaudally
through the middle of the corpus callosum, which was more accurate than the
old one, and the anteroposterior length of this curve could be calculated (length
of corpus callosum). However the distance of any two adjacent points on this
new line were not equidistant, so another b-spline interpolation was performed
on this new middle line, top edge and bottom edge, resulting in a modified
middle line with 400 equidistant points, top edge and bottom edge with 400
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corresponding points but not equidistant. Each point on the middle line
corresponded with a measurement of callosal thickness, and the value of
thicknesses were coded in color and mapped onto the Einstein’s left callosal
space in Fig. A2. The average corpus callosum thickness plot of Einstein is shown
in Fig. 3 (red thick line). The average callosal thickness distribution of Einstein
was coded in color and mapped onto the middle line of Einstein’s callosum on
the left hemisphere (Fig. A2, 4 and 5, top row).
The circularity of corpus callosum is defined as: 4πA/P2, where A is corpus
callosum area and P is perimeter(Ardekani et al., 2013).
4 Measurements of control groups
Image volumes were manually reoriented to a standard coordinate system of
the ICBM-152 brain space using a six-parameter rigid-body transformation with
SPM8 (Statistical Parametric Mapping, Wellcome Trust Centre for Neuroimaging,
Britain), then the non-uniform intensity of images caused by magnetic field
inhomogeneities was removed by N3 (Sled et al., 1998) and SPM8 . The voxel size
of bias corrected image volumes were resampled to 0.2 × 0.2 mm2 in sagittal
plane resolution, with a slice thickness of 0.4 mm. The callosal contour was
delineated on a midsagittal section in which the aqueduct cerebri and the fourth
ventricle were visible. The callosal measurements of the control brains were the
same as Einstein’s brain.
Each individual has a unique brain and corpus callosum, thus their callosal
subdivisions must differ (Witelson, 1989). Each individual’s corpus callosum plot
can be found in Fig. 3A and 3C. To compare the difference between Einstein’s
callosal thickness and that of control brains, the callosal thickness distribution
was subdivided into three sections, and the sections of the control groups were
registered to corresponding sections of Einstein’s corpus callosum. Procedures
are described as follows: the maximal callosal thicknesses in the genu, the
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minimal thickness in the isthmus, and the corresponding numbers of landmark
points in the callosal middle line from 1 to 400 were found in both Einstein’s
corpus callosum and in each individual control’s corpus callosum. The callosal
thickness distributions of Einstein and all individuals were partitioned into three
sections and each section for the individuals was registered to the corresponding
section of Einstein’s corpus callosum with a linear interpolation. The registered
plots of controls are shown in Figs. 3B and 3D, the registered thickness maps are
shown in the right column of Figs. 4 and 5.
In order to measure the average brain volume and weight, the segment
functions of SPM8 and ICBM-152 nonlinear symmetric templates version 2009
(Kim et al., 2011) were employed, and the grey matter (GM) and white matter
(WM) were segmented from the MRI data, respectively. The brain volume was
calculated by summing the volume of GM and WM, thus the brain weight was
calculated with the brain volume multiplied by the average brain density
(1.081g/cm3)(Barber et al., 1970). The callosal contours, middle lines and
thickness maps of Einstein and two control groups are shown in Figs. A2 and
A3. The corpus callosum circularities of controls were calculated as they were for
Einstein’s corpus callosum.
Figure A2 The corpus callosum thickness maps of Einstein and the elderly control
group. The first two color background pictures are Einstein’s left (flipped to a
right view) and right midsagittal surfaces. Each individual corpus callosum was
segmented by 400 equidistant points along the corpus callosum middle line, and
the corresponding thickness of the point on the corpus callosum middle line was
coded in color and mapped onto the individual corpus callosum middle line.
Einstein’s right corpus callosum middle line looks a little different in the splenium
than the left one, which was probably caused by distortion during preservation.
Figure A3 The corpus callosum thickness maps for the youth control group.
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