Brain Imaging and Behavior (2013) 7:300–306
DOI 10.1007/s11682-013-9230-7
ORIGINAL RESEARCH
Impact of body mass index on neuronal fiber bundle lengths
among healthy older adults
Jacob D. Bolzenius & David H. Laidlaw &
Ryan P. Cabeen & Thomas E. Conturo &
Amanda R. McMichael & Elizabeth M. Lane &
Jodi M. Heaps & Lauren E. Salminen & Laurie M. Baker &
John Gunstad & Robert H. Paul
Published online: 7 April 2013
# Springer Science+Business Media New York 2013
Abstract Increased body mass index (BMI) has been
linked to various detrimental health outcomes, including
cognitive dysfunction. Recent work investigating associations between obesity and the brain has revealed decreased
white matter microstructural integrity in individuals with
elevated BMI, independent of age or comorbid health conditions. However, the relationship between high BMI and
white matter fiber bundle length (FBL), which represents a
novel metric of microstructural brain integrity, remains unknown. The present study utilized quantitative tractography
based on diffusion tensor imaging (DTI) to investigate the
relationship between BMI and FBL in 72 otherwise healthy
older adults (24 males, 48 females). All participants were
between 51 and 85 years of age (M=63.26, SD=8.76). Results revealed that elevated BMI was associated with shorter
J. D. Bolzenius (*) : J. M. Heaps : L. E. Salminen : L. M. Baker :
R. H. Paul
University of Missouri-Saint Louis, One
University Boulevard, Stadler Hall 443,
Saint Louis, MO 63121, USA
e-mail: jdbdgf@umsl.edu
D. H. Laidlaw : R. P. Cabeen
Computer Science Department,
Brown University, Providence, RI 02912, USA
T. E. Conturo : A. R. McMichael
Mallinckrodt Institute of Radiology, Washington University
School of Medicine, Saint Louis, MO 63110, USA
E. M. Lane
Vanderbilt University Medical Center, 1211 Medical Center Drive,
Nashville, TN 37232, USA
J. Gunstad
Department of Psychology, Kent State University,
Kent, OH 44242, USA
FBL in the temporal lobe, independent of age (p<.01). In
addition, increased age was associated with shorter frontal,
temporal, and whole brain FBL (all p values<.01). These
findings indicate that, while increased age is an important
factor associated with reduced FBL, high BMI is uniquely
associated with reduced FBL in the temporal lobe. These
data offer evidence for additive adverse effects of high BMI
on the brain, especially in areas already vulnerable to aging
processes and age-related neurodegenerative diseases. Further research is necessary to determine the physiological
mechanisms associated with the shortening of FBL in individuals with high BMI.
Keywords Tractography . BMI . DTI . White matter . Fiber
bundle length . Aging
Introduction
Prevalence of obesity has become a growing public health
concern in the past few decades, particularly in Western
cultures (Flegal et al. 2010). Elevated body fat, measured
using body mass index (BMI), leads to impairments in
cognitive function as well as a host of other health concerns, including cardiovascular disease and type 2 diabetes (Mokdad et al. 2004). Individuals with cardiovascular
disease show impaired cognitive function in executive
function and memory and an increased risk for development of dementia, most notably Alzheimer’s disease (AD;
Gunstad et al. 2007; Gustafson et al. 2003). Elevated BMI
is also associated with cognitive decline across the adult
lifespan, independent of aging processes (Gunstad et al.
2007) or cardiovascular disease (Jagust 2007). Cognitive
deficits appear to be exacerbated by obesity in older age,
Brain Imaging and Behavior (2013) 7:300–306
especially in executive function, memory, and processing
speed (Van den Berg et al. 2009).
White matter integrity in the brain observed with diffusion
tensor imaging (DTI) can also be adversely affected by increased body weight. Evidence suggests that the abundance of
adipocytes seen in obese individuals leads to an overactivation of the inflammatory response to cellular injury,
resulting in damage to oligodendrocytes which comprise myelin in the brain (Griffin 2006; Roth et al. 2005). DTI provides
information about the microstructural integrity of white matter
(e.g. axons, myelin) and water movement within white matter
fibers not captured by traditional magnetic resonance imaging
(MRI; Basser and Pierpaoli 1996). Indices of white matter
fiber integrity such as fractional anisotropy (FA) show decreased fiber integrity in obese individuals compared to
normal-weight and overweight individuals (Stanek et al.
2011). Studies have found specific declines in FA in the body
of the corpus callosum, and increased diffusivity in the
splenium of the corpus callosum and fornix in individuals
with increased BMI (Xu et al. 2011). Other studies suggest
that increased BMI is linked to alterations in myelin and
neuronal structural damage in frontal white matter, a region
already believed to be vulnerable to aging processes, leading
to marked deficits in frontal lobe connectivity and increased
atrophy (Gazdzinski et al. 2008). Reduced FA has also been
observed in temporal lobe structures associated with advanced
age (Rogalski et al. 2012). Collectively, these studies suggest
that DTI has the ability to capture white matter microstructural
abnormalities associated with elevated BMI.
DTI tractography is a method that noninvasively traces
neuronal fiber pathways in the brain (Conturo et al. 1999;
Mori et al. 1999). This method allows for visualization of
coherent bundles of nerve fibers, represented as reconstructed
track lines. It complements other scalar DTI metrics by providing additional detail about the direction and curvature of
white matter pathways coursing through the brain (Correia et
al. 2008). Histologic studies indicate that the lengths of white
matter fibers may be a biomarker of age-related brain degradation (Marner et al. 2003; Tang et al. 1997). Also, evidence
of reduced fiber bundle length (FBL) among individuals with
severe vascular disease compared to healthy controls (Correia
et al. 2008) suggests that FBL may represent a sensitive
neuroimaging index to determine the integrity of white matter
in the brain. Thus, measurement of white matter integrity
using FBL may provide valuable information about changes
in white matter associated with elevated BMI.
Given that previous research suggests decreased white
matter integrity in individuals with high BMI, possibly due
to myelin alterations and neuronal damage (Gazdzinski et al.
2008), it is possible that FBL would be significantly reduced
among individuals with high BMI. The purpose of the present
study was to determine whether older individuals with high
BMI exhibit reduced FBLs in the frontal and temporal lobes
301
compared to older individuals with lower BMI. These regions
were selected because they were shown to have changes
associated with high BMI (Van den Berg et al. 2009). We
hypothesized that BMI and age would be significantly associated with mean length of white matter fiber bundles in each
lobe, and that BMI would uniquely predict FBL in the frontal
and temporal lobes.
Methods
Participants
Seventy-three (73) older adults (24 men, 49 women) between
the ages of 51 and 85 who were enrolled in a study of
cognitive aging were selected for the present study. Participants were recruited from the local community as well as the
Research Participant Registry of the Washington University
Institute of Clinical and Translational Sciences (ICTS). In
order to be considered for the study, all participants were
required to be English speaking and show no evidence of
any medical or psychiatric condition that might affect cognition or mental status. Further, only participants whose BMI
values were in the normal weight, overweight, or obese range
(≥ 18.5 kg/m2) were included in the study. Reasons for exclusion from the study included history of neurological disease
such as dementia, stroke, and Parkinson’s disease. The MiniMental State Examination (MMSE) was administered to identify individuals meeting criterion for dementia, excluding
those with scores below 24. Participants were also excluded
if they reported a history of diabetes, head injury (defined as
loss of consciousness greater than 5 min), alcohol or drug
abuse, or presence of an Axis I psychiatric condition (e.g.,
schizophrenia; bipolar disorder; or current severe, untreated
depression). All participants provided informed consent and
were financially compensated for their participation in the
study. IRB approval was obtained from local institutional
committees involved in the study.
Neuroimaging acquisition
MRI acquisitions were obtained at Washington University in
St. Louis using a head-only Magnetom Allegra 3 T MRI
scanner (Siemens Healthcare, Erlangen, Germany). For maximal stability and quality assurance, no modifications were
made to scanner hardware or software during the course of the
study, and quality assurance checks were carried out daily to
ensure data fidelity. High-performance gradients (max
strength 40 mT/m in a 100-microsecond rise time; maximum
slew rate 400 T/m/s simultaneously on all 3 axes) were used to
minimize scan times. Automated high-order shimming was
utilized. The total time of the MRI scanning session was under
one hour. Each scanning session began with a scout scan
302
consisting of three orthogonal planes to confirm head positioning. Structural images were then obtained, consisting of
T1-weighted magnetization-prepared rapid-acquisition gradient echo (MP-RAGE) imaging, T2-weighted turbo spin echo
(TSE) imaging, and T2-weighted fluid-attenuated inversionrecovery (FLAIR) imaging, as described in Paul et al. (2011).
Slice coverage and field of view (FOV) were determined from
an initial pilot study of a subset of the same participants.
Diffusion-Weighted Imaging (DWI) acquisition
Axial DWI was collected using a custom single-shot
multislice echo-planar tensor-encoded pulse sequence. Diffusion gradients were applied in 31 non-collinear diffusionencoded directions, which included 24 main directions (diffusion weighting of b=996 s/mm2). The pulse sequence and
acquisition parameters were optimized for tractography. Acquisition parameters were designed for whole-brain coverage,
high signal-to-noise ratio (SNR), and minimal artifact, with a
TE of 86.2 ms, a TR of 7.82 s, and 64 contiguous 2.0-mm
slices acquired for each contrast. The acquisition matrix was
128×128 with a 256×256 mm FOV (isotropic 2.0×2.0×
2.0 mm voxels). Two scan repeats were acquired for signal
averaging (72 total acquisitions).
Quantitative diffusion tensor tractography
Using FSL FLIRT (mutual information metric; Jenkinson et
al. 2002), each individual’s DWI images and diffusionencoding vectors were registered to the I0 image in order to
correct for subject motion within the scanner. Using Diffusion
Toolkit’s dti_recon (Wang et al. 2007), tensors and FA values
were calculated from the DWIs, b values, and diffusionencoding vectors. Trilinear interpolation was used to calculate
the diffusion tensor field (Zhukov and Barr 2002). From the
tensor field, we then reconstructed tracks representing white
matter fiber bundles, using a continuous tracking (FACT)
algorithm (Mori et al. 1999), with one seed per voxel. The
tracks were stopped when FA≤0.15 or step angle≥35°. Tracks
measuring less than 10 mm in length were excluded from the
analysis. The tractography analyses were shown to be consistent in previous work by our group (Correia et al. 2008), and
results in this study compared well with known white matter
structures.
Measurement of mean fiber bundle length associated
with a specific lobe
The FA image was registered to the ICBM T1 atlas using
FLIRT (mutual information metric; Mazziotta et al. 2001).
ICBM T1 lobular labels were then used to transform this
registration to the DWI space (Jenkinson et al. 2002) using
nearest-neighbor interpolation. Custom software was utilized
Brain Imaging and Behavior (2013) 7:300–306
to segregate tracks connected to the frontal, parietal, temporal,
and occipital lobes. A track was assigned to a lobe if it had at
least one endpoint in either the left or right lobe. If a track was
found to have endpoints in two different lobes, it was assigned
to both lobes. Therefore, tracks could reside entirely in an
individual lobe, could project to another ipsilateral lobe, or
could cross to the contralateral side. The mean length of all the
tracks associated with a given lobe was then calculated using
custom software. This measure was based on each individual’s
unique anatomy, so co-registration between multiple participants was not required. Prior to statistical comparison, all
mean FBL measures were normalized to intracranial volume.
Intracranial volume was estimated by adding three probability
maps of voxel identity together. Measures of FBL then
underwent head size correction using normalized algorithms
for streamtube quantity, total sum of streamtube length, and
weighted measures of total length for linear and fractional
anisotropy. Details of normalized algorithms are explained in
a previous paper (Correia et al. 2008).
Statistical analysis
BMI was calculated for each participant based on the height
and weight measured in our lab. One participant was identified as an outlier after comparing z-scores of FBL across all
four brain lobes and whole-brain FBL and was removed from
the statistical analyses. As a result, the total sample size was
72 participants (24 men, 48 women). Pearson’s correlation
coefficients were computed to examine the relationships between age, gender, years of education, BMI, and white matter
FBL by lobe to identify potential covariates in the subsequent
analyses. Hierarchical regression analyses were performed to
test the main hypothesis that BMI was related to FBL. In the
first step, the demographic variables (age, gender, years of
education) that were significantly correlated with FBL were
entered as independent variables, with white matter FBL by
lobe as the dependent variable. In the second step BMI was
entered to determine its unique impact on FBL by lobe.
Results
Participant demographics and BMI values are listed in Table 1.
Pearson’s correlation coefficients revealed moderate negative
correlations between BMI and regional brain FBL (Table 2).
BMI was negatively correlated with the mean FBL of tracks
associated with the temporal lobe (p=.002). Age was negatively correlated with frontal FBL (p=.001), temporal FBL
(p<.001), and whole brain FBL (p=.001), and a trend was
observed for parietal FBL (p=.018).
Hierarchical regression analyses revealed that only temporal lobe FBL was significantly predicted by BMI after
controlling for age (F(2, 69)=11.816, p<.001, R2 =.255, R2
Brain Imaging and Behavior (2013) 7:300–306
Table 1 Demographic
characteristics
303
Demographic characteristics
N=72 (24 males, 48 females)
a
Calculated from a total sample
of 71 participants
Variable
Mean
SD
Min
Max
Age
Education
BMI
MMSEa
8.76
2.51
3.56
1.46
51
11
18.60
24
85
20
33.45
30
High Blood Pressure
High Cholesterol
63.26
15.46
25.99
28.68
Cases (%)
33.3
44.8
Cardiovascular Disease
23.5
change attributed to BMI=.093). All other hierarchical regression models, including the relationship between BMI
plus age and frontal lobe FBL, were significant except for
the impact of BMI plus age on parietal lobe FBL. However,
the unique contribution of BMI to these models did not
reach significance (Table 3).
Discussion
To our knowledge, this study is the first to utilize measurement of white matter fiber bundle lengths to investigate the
impact of BMI on white matter in a sample of otherwise
healthy older individuals. Increases in both BMI and age were
found to predict decreases in white matter FBL throughout
several regions of the brain, though these decreases were
largely driven by the effects of age. After controlling for the
robust influence of age, BMI was shown to significantly
predict white matter FBL in the temporal lobe. Results of
correlation analyses were consistent with this by demonstrating a significant relationship between BMI and temporal lobe
FBL (Fig. 1). Significant correlations were also observed
between age and white matter FBL in two of the four major
brain areas investigated in this study, as well as whole brain
FBL. Overall, the results suggest that elevated BMI is associated with white matter changes evidenced by shorter temporal
FBL, even after parsing out the effects of increased age. This
finding suggests that elevated BMI may be associated with an
accelerated course of “normal aging”, and an acceleration of
age-related changes in microstructural integrity in these brain
regions.
Table 3 Hierarchical regression results for fiber bundle length
Hierarchical regression results for fiber bundle length
Table 2 Correlations between Age, BMI, and fiber bundle length
Variable
β
R2
Correlations between Age, BMI and fiber bundle length
Whole Brain
Age
Gender
BMI
−0.380
−0.297
−0.207
0.222
0.222
9.863***
0.264
0.042
3.840
−0.360
−0.118
0.142
0.155
0.142
0.014
11.557**
1.107
−0.358
−0.309
0.162
0.255
0.162
0.093
13.498***
8.657**
0.253
−0.164
0.071
0.098
0.071
0.027
5.346*
2.049
−0.278
0.005
0.077
0.077
0.077
0.000
5.871*
0.969
Brain Region
Age
Whole Brain
Frontal Lobe
Temporal Lobe
Occipital Lobe
Parietal Lobe
BMI
Whole Brain
Frontal Lobe
Temporal Lobe
Occipital Lobe
Parietal Lobe
r
p value
−0.382
−0.376
−0.402
−0.225
−0.278
0.001*
0.001*
<0.001*
0.058
0.018
−0.230
−0.169
−0.360
−0.186
−0.035
0.052
0.155
0.002*
0.119
0.768
*Statistically significant at a Bonferroni-corrected p-value threshold of
p<.01 (corrected for 5 brain regions)
Frontal Lobe
Age
BMI
Temporal Lobe
Age
BMI
Occipital Lobe
Education
BMI
Parietal Lobe
Age
BMI
*p<.05, **p<.01, ***p<.001
R2 change
F change
304
Brain Imaging and Behavior (2013) 7:300–306
Fig. 1 Scatter plot illustrating
correlation between BMI and
temporal lobe FBL
40.00
Mean Temporal FBL (mm)
35.00
30.00
25.00
20.00
15.00
10.00
5.00
0.00
10.0
15.0
20.0
25.0
30.0
35.0
40.0
BMI
The observed reductions in temporal FBL seen in the
current study may represent early indicators of temporal lobe
dysfunction. Impairments in cognitive functioning related to
the temporal lobe (especially memory) occur in both the
elderly population and in adults with elevated BMI (Brickman
et al. 2006; DeCarli et al. 2005; Gunstad et al. 2007). While
cognitive domains related to the frontal lobe are commonly
affected in both elderly individuals (Greenwood 2000) and in
adults with high BMI (Gunstad et al. 2007), no statistically
significant relationship between BMI and frontal FBL was
seen in the current study. This may be due to underrepresentation of obese participants in the current study; only
11 % (n=8) of our sample were classified as “obese” based on
BMI value. This small sample of participants on the high end
of the BMI spectrum may have attenuated the potential association between BMI and frontal lobe FBL. Another reason
for this discrepancy might be that the cohort in the current
study was relatively young, especially in the context of cognitive impairment and dementia (Evans et al. 1989). These
disorders tend to proliferate later in life and mainly affect
temporal structures before later affecting the frontal lobes
(Braak and Braak 1991; Van Hoesen et al. 1991). Overall,
evidence from past research combined with results of the
current study suggest that high BMI in older adult populations
is associated with evidence of accelerated aging processes on
the brain, which are manifested by the shortening of fiber
bundles, especially fiber bundles associated with the temporal
lobe. Future studies are necessary to investigate the relationships between FBL, BMI, and cognitive function.
Past research using DTI to investigate the effect of elevated BMI has shown similar reductions in white matter
microstructural integrity. Studies have shown reduced FA in
the corpus callosum in individuals with elevated BMI, indicating a decrease in the directionality of diffusion along
white matter tracks (Stanek et al. 2011; Xu et al. 2011).
Other studies have measured higher radial diffusivity (RD)
associated with increased BMI (Mueller et al. 2011). These
prior DTI findings suggest a reduction in myelination in
individuals with high BMI, consistent with evidence of
brain tissue injury (Mueller et al. 2011). Results of the
current study, which exhibited shorter FBL in temporal
white matter, provide support for these past findings. A
mechanism of histologic fiber length shortening has been
suggested (Marner et al. 2003; Tang et al. 1997), evidenced
by a pattern of patchy microscopic areas of myelin loss
and/or axonal damage that collapse, thereby shortening the
overall fiber length. Our data extend the findings of prior
research by showing that elevated BMI is related to alterations in white matter integrity that result in the observed
reduction in FBL, even after controlling for the effect of age.
In general, a process of chronic progressive myelin loss and
fiber bundle shortening may lead to impaired neural transmission and connectivity between brain regions, which may
contribute to the pattern of global functioning and cognitive
Adipocytes
Weight gain
Cytokines
Leptin
Neuronal
pathology
Ca2+
APP
response
Apoptosis &
astrogliosis
White matter
damage
Fig. 2 Flow chart illustrating the theorized mechanistic model behind
reductions in fiber bundle length associated with elevated BMI. The
model depicts a cascade of events initiated by weight gain and leads to
white matter damage
Brain Imaging and Behavior (2013) 7:300–306
deficits commonly seen in individuals with elevated BMI
(Gunstad et al. 2007).
Previous research has identified several mechanisms by
which obesity leads to white matter abnormalities (Fig. 2).
Normal-weight individuals have relatively low numbers of
adipocytes, leading to lower levels of the hormone leptin
(Wisse 2004). Leptin plays a key role in regulation of the
inflammatory response, and is specifically involved in the
expression of pro-inflammatory cytokines (Wisse 2004). In
obese individuals, the increased quantity of adipocytes leads
to excessive levels of circulating leptin (Considine et al.
1996). Since obesity is a chronic disease of leptin
hypersecretion, production of pro-inflammatory cytokines is
continuously elevated in these individuals (Wisse 2004). Elevated levels of cytokines lead to hyperphosphorylated tau
protein and neurofibrillary tangles, influencing dystrophic
neurite growth (Griffin 2006). Dystrophic neurite formation
stimulates the production of β-amyloid precursor protein,
which further stimulates expression of the interleukin (IL-1
and IL-6) and S100β cytokines (Mrak et al. 1996). This
continuous cycle induces increased intracellular calcium concentrations, promoting premature apoptosis and astrogliosis
(Griffin 2006). These microphysiological changes have been
shown to cause disruptions in white matter via damage to
oligodendrocytes (Roth et al. 2005), which offers support for
the alterations in white matter integrity seen in our study.
Though the shorter temporal fiber bundles observed in the
current study provides a possible mechanism for the progression from “normal aging” to pathological aging in people with
high BMI, the use of FBL as a measure of brain pathology
requires additional study. Our tractography data were limited
by the use of only one seed per voxel, despite literature
suggesting that tractography computations benefit most from
using 10–15 seeds per voxel (Cheng et al. 2012). Further,
while MR spectroscopy measures of axonal viability are associated with BMI (Gazdzinski et al. 2008), the causal nature of
the relationship between elevated BMI and shorter FBL, and
the reason for the selective regional track shortening seen in the
current study have yet to be determined. However, the combination of findings from healthy aging studies (e.g. Barrick et al.
2010) and BMI studies (e.g. Stanek et al. 2011) suggests that
examining white matter using FBL may provide important
information regarding overall brain health. Delineating the
relationships between high BMI, aging processes, cognitive
functioning, and FBL represent important areas of future research in brain aging, and will further evaluate the validity of
FBL as a measure of white matter integrity and connectivity.
Additionally, investigating the potential role of genetic status
on this relationship represents an important area of future
research. Research has implicated several genetic risk factors
involved in the inflammatory response associated with high
BMI, including CRP, IL-1β, and IL-6 (Brull et al. 2003;
D’Aiuto et al. 2004; Latkovskis et al. 2004). Genetic
305
polymorphisms of the renin-angiotensinogen system and other
genetic risks for vascular pathology (e.g. ApoE) have also been
linked to elevated BMI levels (Schmidt et al. 2012).
Overall, results of this study suggest that temporal lobe
FBL provides a sensitive marker of brain integrity and may
serve as an early indicator of age-related brain changes,
especially in individuals with elevated BMI. The observed
association between BMI and temporal FBL has a potential
relationship to the known increased prevalence of AD in
individuals with high BMI (Gustafson et al. 2003), and the
appearance of pathological changes in the temporal lobes in
the earliest stages of AD. If reductions in lengths of fiber
bundles seen in the current study are indicative of BMIrelated neuropathology, then FBL measurements may have a
role in predicting cognitive decline even in a pre-clinical,
relatively healthy population.
Acknowledgments Study Funding: Supported by NIH/NINDS grant
number R01 NS052470 and R01 NS039538, and NIH/NIMH grant
R21 MH090494. Recruitment database searches were supported in part
by NIH/NCRR grant UL1 TR000448.
Disclosure statement There are no actual or potential conflicts of
interest for any of the authors on this manuscript.
References
Barrick, T. R., Charlton, R. A., Clark, C. A., & Markus, H. S. (2010).
White matter structural decline in normal ageing: a prospective
longitudinal study using tract-based spatial statistics.
NeuroImage, 51(2), 565–577.
Basser, P. J., & Pierpaoli, C. (1996). Microstructural and physiological
features of tissues elucidated by quantitative-diffusion-tensor
MRI. Journal of Magnetic Resonance. Series B, 111(3), 209–219.
Braak, H., & Braak, E. (1991). Neuropathological stageing of Alzheimerrelated changes. Acta Neuropathologica, 82(4), 239–259.
Brickman, A. M., Zimmerman, M. E., Paul, R. H., Grieve, S. M., Tate,
D. F., Cohen, R. A., et al. (2006). Regional white matter and
neuropsychological functioning across the adult lifespan. Biological Psychiatry, 60(5), 444–453.
Brull, D. J., Serrano, N., Zito, F., Jones, L., Montgomery, H. E.,
Rumley, A., et al. (2003). Human CRP gene polymorphism influences CRP levels implications for the prediction and pathogenesis of coronary heart disease. Arteriosclerosis, Thrombosis, and
Vascular Biology, 23(11), 2063–2069.
Cheng, H., Wang, Y., Sheng, J., Sporns, O., Kronenberger, W. G.,
Mathews, V. P., et al. (2012). Optimization of seed density in
DTI tractography for structural networks. Journal of Neuroscience Methods, 203(1), 264–272.
Considine, R. V., Sinha, M. K., Heiman, M. L., Kriauciunas, A., Stephens, T. W., Nyce, M. R., et al. (1996). Serum immunoreactiveleptin concentrations in normal-weight and obese humans. The New
England Journal of Medicine, 334(5), 292–295.
Conturo, T. E., Lori, N. F., Cull, T. S., Akbudak, E., Snyder, A. Z.,
Shimony, J. S., et al. (1999). Tracking neuronal fiber pathways in
the living human brain. Proceedings of the National Academy of
Sciences, 96(18), 10422–10427.
306
Correia, S., Lee, S. Y., Voorn, T., Tate, D. F., Paul, R. H., Zhang, S., et
al. (2008). Quantitative tractography metrics of white matter
integrity in diffusion-tensor MRI. NeuroImage, 42(2), 568.
D’Aiuto, F., Parkar, M., Brett, P. M., Ready, D., & Tonetti, M. S.
(2004). Gene polymorphisms in pro-inflammatory cytokines are
associated with systemic inflammation in patients with severe
periodontal infections. Cytokine, 28(1), 29–34.
DeCarli, C., Massaro, J., Harvey, D., Hald, J., Tullberg, M., Au, R., et
al. (2005). Measures of brain morphology and infarction in the
Framingham Heart Study: establishing what is normal. Neurobiology of Aging, 26(4), 491–510.
Evans, D. A., Funkenstein, H. H., Albert, M. S., Scherr, P. A., Cook, N.
R., Chown, M. J., et al. (1989). Prevalence of Alzheimer’s disease
in a community population of older persons. JAMA: The Journal
of the American Medical Association, 262(18), 2551–2556.
Flegal, K. M., Carroll, M. D., Ogden, C. L., & Curtin, L. R.
(2010). Prevalence and trends in obesity among US adults,
1999–2008. JAMA: The Journal of the American Medical
Association, 303(3), 235–241.
Gazdzinski, S., Kornak, J., Weiner, M. W., & Meyerhoff, D. J. (2008).
Body mass index and magnetic resonance markers of brain integrity in adults. Annals of Neurology, 63(5), 652–657.
Greenwood, P. M. (2000). The frontal aging hypothesis evaluated. Journal of the International Neuropsychological Society, 6(6), 705–726.
Griffin, W. S. T. (2006). Inflammation and neurodegenerative diseases.
The American Journal of Clinical Nutrition, 83(2), 470S–474S.
Gunstad, J., Paul, R. H., Cohen, R. A., Tate, D. F., Spitznagel, M. B., &
Gordon, E. (2007). Elevated body mass index is associated with
executive dysfunction in otherwise healthy adults. Comprehensive
Psychiatry, 48(1), 57–61.
Gustafson, D., Rothenberg, E., Blennow, K., Steen, B., & Skoog, I.
(2003). An 18-year follow-up of overweight and risk of
Alzheimer disease. Archives of Internal Medicine, 163(13), 1524.
Jagust, W. (2007). What can imaging reveal about obesity and the
brain? Current Alzheimer Research, 4(2), 135–139.
Jenkinson, M., Bannister, P., Brady, M., & Smith, S. (2002). Improved
optimization for the robust and accurate linear registration and
motion correction of brain images. NeuroImage, 17(2), 825–841.
Latkovskis, G., Licis, N., & Kalnins, U. (2004). C-reactive protein levels and common polymorphisms of the interleukin-1
gene cluster and interleukin-6 gene in patients with coronary
heart disease. European Journal of Immunogenetics, 31(5),
207–213.
Marner, L., Nyengaard, J. R., Tang, Y., & Pakkenberg, B. (2003).
Marked loss of myelinated nerve fibers in the human brain with
age. The Journal of Comparative Neurology, 462(2), 144–152.
Mazziotta, J., Toga, A., Evans, A., Fox, P., Lancaster, J., Zilles, K., et
al. (2001). A probabilistic atlas and reference system for the
human brain: International Consortium for Brain Mapping
(ICBM). Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, 356(1412), 1293–1322.
Mokdad, A. H., Marks, J. S., Stroup, D. F., & Gerberding, J. L.
(2004). Actual causes of death in the United States, 2000.
Brain Imaging and Behavior (2013) 7:300–306
JAMA: The Journal of the American Medical Association,
291(10), 1238–1245.
Mori, S., Crain, B. J., Chacko, V. P., & Van Zijl, P. (1999). Threedimensional tracking of axonal projections in the brain by magnetic resonance imaging. Annals of Neurology, 45(2), 265–269.
Mrak, R. E., Sheng, J. G., & Griffin, W. S. T. (1996). Correlation of
astrocytic S100 [beta] expression with dystrophic neurites in
amyloid plaques of Alzheimer’s disease. Journal of Neuropathology and Experimental Neurology, 55(4), 273–279.
Mueller, K., Anwander, A., Möller, H. E., Horstmann, A., Lepsien, J.,
Busse, F., et al. (2011). Sex-dependent influences of obesity on
cerebral white matter investigated by diffusion-tensor imaging.
PLoS One, 6(4), e18544.
Paul, R., Lane, E. M., Tate, D. F., Heaps, J., Romo, D. M., Akbudak, E., et
al. (2011). Neuroimaging signatures and cognitive correlates of the
Montreal cognitive assessment screen in a nonclinical elderly sample. Archives of Clinical Neuropsychology, 26, 454–460.
Rogalski, E., Stebbins, G. T., Barnes, C. A., Murphy, C. M., Stoub, T.
R., George, S., et al. (2012). Age-related changes in
parahippocampal white matter integrity: a diffusion tensor imaging study. Neuropsychologia, 50(8), 1759–1765.
Roth, A. D., Ramírez, G., Alarcón, R., & Von Bernhardi, R. (2005).
Oligodendrocytes damage in Alzheimer’s disease: beta amyloid
toxicity and inflammation. Biological Research, 38(4), 381.
Schmidt, H., Freudenberger, P., Seiler, S., & Schmidt, R. (2012).
Genetics of subcortical vascular dementia. Experimental Gerontology, 47(11), 873–877.
Stanek, K. M., Grieve, S. M., Brickman, A. M., Korgaonkar, M.
S., Paul, R. H., Cohen, R. A., et al. (2011). Obesity is
associated with reduced white matter integrity in otherwise
healthy adults. Obesity, 19(3), 500–504.
Tang, Y., Nyengaard, J., Pakkenberg, B., & Gundersen, H. J. (1997).
Age-induced white matter changes in the human brain: a stereological investigation. Neurobiology of Aging, 18(6), 609–615.
Van den Berg, E., Kloppenborg, R. P., Kessels, R. P. C., Kappelle, L. J.,
& Biessels, G. J. (2009). Type 2 diabetes mellitus, hypertension,
dyslipidemia and obesity: a systematic comparison of their impact
on cognition. BBA-Mol Basis Dis, 1792(5), 470–481.
Van Hoesen, G. W., Hyman, B. T., & Damasio, A. R. (1991). Entorhinal
cortex pathology in Alzheimer’s disease. Hippocampus, 1(1), 1–8.
Wang, R., Benner, T., Sorensen, A. G., & Wedeen, V. J. (2007). Diffusion
toolkit: a software package for diffusion imaging data processing
and tractography. Proc Intl Soc Mag Reson Med, 15, 3720.
Wisse, B. E. (2004). The inflammatory syndrome: the role of adipose
tissue cytokines in metabolic disorders linked to obesity. Journal
of the American Society of Nephrology, 15(11), 2792–2800.
Xu, J., Li, Y., Lin, H., Sinha, R., & Potenza, M. N. (2011). Body mass
index correlates negatively with white matter integrity in the
fornix and corpus callosum: A diffusion tensor imaging study.
Human Brain Mapping. Dec. 3 [epub ahead of print].
Zhukov, L., & Barr, A. H. (2002). Oriented tensor reconstruction:
Tracing neural pathways from diffusion tensor MRI. Visualization, 2002. VIS 2002. IEEE. pp. 387–394.