NeuroImage 185 (2019) 556–564
Contents lists available at ScienceDirect
NeuroImage
journal homepage: www.elsevier.com/locate/neuroimage
Aberrant memory system connectivity and working memory performance in
subjective cognitive decline
Raymond P. Viviano a, b, Jessica M. Hayes a, Patrick J. Pruitt b, Zachary J. Fernandez b,
Sanneke van Rooden c, Jeroen van der Grond c, Serge A.R.B. Rombouts c, d,
Jessica S. Damoiseaux a, b, d, *
a
Department of Psychology, Wayne State University, 5057 Woodward Ave. 7th Floor Suite 7908, Detroit, MI, 48201, United States
Institute of Gerontology, Wayne State University, 87 E. Ferry St., Detroit, MI, 48202, United States
c
Department of Radiology, Leiden University Medical Center, P.O. Box 9600, 2300, RC, Leiden, Netherlands
d
Institute of Psychology, Leiden University, PO Box 9500, 2300, RA, Leiden, Netherlands
b
A R T I C L E I N F O
A B S T R A C T
Keywords:
Subjective cognitive decline
Functional connectivity
Neurite density
Visual working memory
Memory systems
Subjective cognitive decline, a perceived worsening of cognitive functioning without objective deficit on
assessment, could indicate incipient dementia. However, the neural correlates of subjective cognitive decline as
assessed by magnetic resonance imaging remain somewhat unclear. Here, we evaluated differences in functional
connectivity across memory regions, and cognitive performance, between healthy older adults aged 50 to 85 with
(n ¼ 35, Age ¼ 68.5 7.7, 22 female), and without (n ¼ 48, Age ¼ 67.0 8.8, 29 female) subjective cognitive
decline. We also evaluated neurite density, fractional anisotropy, and mean diffusivity of the parahippocampal
cingulum, cingulate gyrus cingulum, and uncinate fiber bundles in a subsample of participants (n ¼ 37). Participants with subjective cognitive decline displayed lower average functional connectivity across regions of a putative posterior memory system, and lower retrosplenial-precuneus functional connectivity specifically, than those
without memory complaints. Furthermore, participants with subjective cognitive decline performed poorer than
controls on visual working memory. However, groups did not differ in cingulum or uncinate diffusion measures.
Our results show differences in functional connectivity and visual working memory in participants with subjective
cognitive decline that could indicate potential incipient dementia.
1. Introduction
Subjective cognitive decline (SCD) is a putative, preclinical stage of
Alzheimer's disease marked by perceived deterioration in cognitive
functioning, in any domain, without overt deficit (Jessen et al., 2014a).
Self-report of cognitive decline or memory issues constitutes a criterion
for mild cognitive impairment (American Psychiatric Association, 2013;
Petersen et al., 1999). However, associations between self-perception of
cognitive functioning and objective cognitive deficits are complex
(Mitchell, 2008). In some instances, cognitive decline may hinder the
ability to make correct self-judgments regarding cognition; that is,
objective decline could occur without perception of decline (anosognosia). On the other hand, individuals may experience worrisome subjective decline in memory ability, but test within a normal range on
neuropsychological assessment. Taken together, these notions diminish
the predictive power of cognitive complaints alone, or the lack thereof,
for determining current dementia status. However, evidence indicates
that these cognitive complaints are predictive of future decline and may
demarcate incipient dementia that precedes mild cognitive impairment
(Gifford et al., 2014; Jessen et al., 2010, 2014b; Reisberg et al., 2008,
2010).
As worrisome cognitive complaint may predict future conversion to
mild cognitive impairment or probable Alzheimer's disease, it is important to understand the biological properties of this potential preclinical
stage to determine targets for preventative intervention. Previous investigations have determined that individuals with SCD exhibit global
atrophy patterns similar to Alzheimer's disease (Peter et al., 2014).
Furthermore, previous analyses have observed specific volume
* Corresponding author. Institute of Gerontology, Wayne State University, 87 E. Ferry St., Detroit, MI, 48202, United States.
E-mail addresses: rviviano@wayne.edu (R.P. Viviano), jessica.hayes2@wayne.edu (J.M. Hayes), pruittpj@wayne.edu (P.J. Pruitt), eh3701@wayne.edu
(Z.J. Fernandez), S.van_Rooden@lumc.nl (S. van Rooden), J.van_der_Grond@lumc.nl (J. van der Grond), S.A.R.B.Rombouts@lumc.nl (S.A.R.B. Rombouts), j.s.
damoiseaux@fsw.leidenuniv.nl, damoiseaux@wayne.edu (J.S. Damoiseaux).
https://doi.org/10.1016/j.neuroimage.2018.10.015
Received 20 July 2018; Received in revised form 3 October 2018; Accepted 4 October 2018
Available online 9 October 2018
1053-8119/© 2018 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
R.P. Viviano et al.
NeuroImage 185 (2019) 556–564
demographic and cognitive measures including Wechsler Memory Scale
IV indices, personality, and depression. We anticipated no difference
between groups on demographic or cognitive metrics. We also evaluated
APOE ε4 carrier status differences, as APOE ε4 carrier status is one of the
most important risk factors for Alzheimer's disease (Strittmatter et al.,
1993), anticipating greater odds of APOE ε4 status in SCD.
reductions in hippocampus, amygdala, parahippocampal, entorhinal,
temporal, and frontal cortices in older individuals with SCD compared to
those without (Hafkemeijer et al., 2013; Jessen et al., 2006; Saykin et al.,
2006; Striepens et al., 2010; van der Flier et al., 2004). Moreover, longitudinal analysis of hippocampal atrophy predicts SCD development at
follow-up measurements, indicating that biological change may underlie
perceived deficit in memory (Cherbuin et al., 2015).
Examination of white matter fiber tract diffusion characteristics have
also identified features that separate healthy older adults with and
without SCD. Most studies to date, except for Yasuno et al. (2015), have
observed lower fractional anisotropy and greater mean diffusivity across
the white matter, and in the cingulum bundle specifically (Hong et al.
(2015); Li et al. (2016)). These results are similar in spatial location and
direction to observed results in mild cognitive impairment and Alzheimer's disease (Rose et al., 2006; Salat et al., 2010). Furthermore,
decreased fractional anisotropy in the right posterior cingulum bundle
associates with lower Mini-Mental State Examination scores, hinting that
posterior cingulate white matter is important for higher cognitive function (Bai et al., 2009). Thus, diffusion characteristics of the cingulum
could predict conversion from SCD to objective decline.
Although multiple structural MRI studies consistently identify gray
matter volume reductions and lower cingulum fractional anisotropy in
SCD, limited observations exist in the extant resting-state functional
connectivity literature. Yasuno et al. (2015) noted lower connectivity
between retrosplenial and medial prefrontal cortices in SCD. However,
Hafkemeijer et al. (2013) observed higher default mode network connectivity, including right hippocampus, in SCD. Due to contrasting results
in the extant literature, we aimed to evaluate functional connectivity
differences between memory regions to better understand brain characteristic differences between healthy older adults with and without SCD
using the two cortical memory systems framework of Ranganath and
Ritchey (2012). Heterogeneity of the hippocampus, with structural and
functional connectivity differences along the long-axis, is a major
component of this framework. The anterior hippocampus connects
directly to the amygdala, entorhinal, and perirhinal cortex (Poppenk
et al., 2013; Ranganath and Ritchey, 2012). Furthermore, the uncinate
fasciculus mediates functional connectivity of the anterior hippocampus
to orbitofrontal and ventromedial prefrontal cortex through intermediate
entorhinal/perirhinal cortex connectivity; though, anatomic studies have
not identified direct hippocampal connections through this tract (Von
Der Heide et al., 2013). The posterior hippocampus connects directly and
indirectly to default mode network cortical regions, i.e., retrosplenial,
posterior cingulate, inferior parietal, precuneus, and medial prefrontal
cortices (Adnan et al., 2016; Buckner et al., 2008; Kahn et al., 2008;
Poppenk et al., 2013; Qin et al., 2016; Ranganath and Ritchey, 2012).
Posterior hippocampal connectivity to default mode regions is ultimately
mediated by the cingulum bundle (Heilbronner and Haber, 2014). We
chose to work within this framework to respect the heterogeneity of the
hippocampus and to examine the effect of SCD on connectivity across
both memory systems. We hypothesized that average posterior memory
system functional connectivity would be lower in older adults with
memory complaints compared to those without such complaints. This
hypothesis contrasts the results of Hafkemeijer et al. (2013), but agrees
with Yasuno et al. (2015), and would be in same direction as results
observed in Alzheimer's disease (Greicius et al., 2004). Furthermore, we
anticipated lower functional connectivity specifically between medial
prefrontal cortex and retrosplenial cortex in SCD, following Yasuno et al.
(2015), as well as lower connectivity between posterior hippocampus
and retrosplenial cortex, as decreased connectivity between these regions
has been observed in Alzheimer's disease and mild cognitive impairment
(Greicius et al., 2004; Wang et al., 2006).
We also evaluated uncinate and cingulum diffusion characteristics in
SCD with diffusion weighted images, and anticipated lower neurite
density and fractional anisotropy, and higher mean diffusivity based on
previously noted observations in SCD (Hong et al., 2015; Li et al., 2016).
We also compared individuals with and without SCD on a variety of
2. Methods
2.1. Participant recruitment
Data were available for 94 participants at the time of analysis; however, we excluded 11 participants due to missing MRI data, MMSE scores
<25, left-handedness, or self-report of repetitive thoughts during the
resting-state fMRI scan (e.g. counting) on a post-scan questionnaire. One
participant used opioid medication prior to the scan session. Thus, T1
structural and resting-state functional images were available for 83
healthy older adults from Detroit, United States, and Leiden, the
Netherlands (mean (M) age ¼ 68.5 years, standard deviation (SD) ¼ 7.6;
51 females). Of the 83 participants, 35 had SCD (M age ¼ 68.5 years,
SD ¼ 7.7; 22 females) and 48 did not (M age ¼ 67.0 years, SD ¼ 8.8; 29
females). Diffusion images were available for 47 participants scanned in
the United States. We excluded 8 participants for reasons listed above,
and 2 additional participants because the diffusion software exited in
error during processing. Thus, 37 participants composed the analyzed
diffusion data set (10 with and 27 without SCD).
Recruitment at Wayne State University occurred through memory
clinics, senior centers, and communities around Metro Detroit, Michigan,
and at the Leiden University Medical Center through clinics and centers
around Leiden in the Netherlands. Review boards approved the study for
both sites. Exclusion criteria included a history of neurological and
psychiatric disorders, cardiovascular disease, brain injury, cancer, psychotropic medication use, and magnetic resonance contraindications.
Individuals categorized as SCD answered “yes” to the following questions: “Do you have memory complaints? If yes, do these complaints
worry you?” Participants with SCD had to be worried about their professed memory issues, as previous analysis suggests that it is mainly those
who worry about their perceived decline that have an elevated risk of
conversion to Alzheimer's disease (Jessen et al., 2010). Most participants
with SCD (34 of 35) sought professional medical advice for their complaints prior to participation but were considered cognitively normal at
the time. All participants were right-handed as assessed by the Edinburgh
Handedness Inventory (Oldfield, 1971), and had scores 25 on the
Mini-Mental State Examination (Folstein et al., 1975), which is considered within the cognitively normal range (Tombaugh and Mcintyre,
1992). Furthermore, all SCD participants performed in the cognitively
normal range as determined by either clinical assessment or performance
on Wechsler Memory Scale VI indices of no less than 1.5 standard deviations below the normative mean. All participants provided informed
consent prior to participation.
2.2. Demographic and neuropsychological assessment
In Detroit, the Wechsler Abbreviated Scale of Intelligence II (Wechsler
and Hsiao-pin, 2011) evaluated participant IQ. In Leiden, the block
design, vocabulary, matrix reasoning, and similarities subtests of the
Dutch version of the Wechsler Adult Intelligence Scale III (Wechsler,
1997) determined equivalent IQ. We evaluated memory function with
the adult battery of the Wechsler Memory Scale IV (Wechsler, 2009). We
converted subscale scores to proportional scores by dividing the total
subscale score by the maximum possible. We then created auditory, visual, visual working memory, immediate, and delayed memory index
scores by averaging subcategories of proportional scores for group
comparison, as in Hayes et al. (2017).
Previous investigations have determined positive associations between depression scores and SCD (Balash et al., 2013; de Guzman et al.,
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2.4.1. Structural image processing
To prepare for manual hippocampal region of interest placement,
realignment of images with 3D Slicer ensured that the bicommissural line
was parallel to the y-axis of the voxel-space mesh grid, and corrected for
head tilt and yaw (Supplementary Figure 1). Image resampling enforced
0.5 mm isotropic voxels. After realignment and resampling, we extracted
non-brain tissue (i.e., skull and meninges) with the FSL brain extraction
tool (Smith, 2002), and created gray matter segmentation maps with
FSL's automated segmentation tool (Zhang et al., 2001).
2015; Montejo et al., 2011; Plotkin et al., 1985), and between SCD and
neuroticism and conscientiousness (Ponds and Jolles, 1996; Reid and
MacLullich, 2006; Slavin et al., 2010). Thus, we evaluated depression
with the Geriatric Depression Scale and the Beck Depression Inventory II
(Beck et al., 1996; Yesavage et al., 1983) and neuroticism and conscientiousness with the Big Five Inventory (Goldberg, 1990). It is important
to note that the Geriatric Depression Scale contains a question that could
relate to perceived memory functioning: 14) “Do you feel you have more
problems with memory than most?” Therefore, we compared groups with
and without this question, and performed a Fisher's Exact test to evaluate
differential participant responding to this question. We have previously
reported on these measures for a subset of our current sample (Hayes
et al., 2017).
2.4.2. Resting-state functional connectivity analysis
Processing included: removal of the first five image volumes to account for early field inhomogeneities, motion correction (Jenkinson
et al., 2002), non-brain structure removal (Smith, 2002), spatial
smoothing (6 mm FWHM), and 4D-grand-mean-scaling. We used
ICA-based Automatic Removal of Motion Artifacts (Pruim et al., 2015) to
remove motion artifacts. Images remained in native-space.
We manually defined anterior and posterior hippocampal coordinates
in participant structural space to ensure proper placement, following
head and body definitions as in Daugherty et al. (2015). The center for
the anterior hippocampus along the long axis was the coronal coordinate
between the center of the mammillary bodies and the last coronal slice
where the uncal apex was visible. The center of the posterior hippocampus was the coronal slice between the uncal apex and the slice where
the fornices ascended from the fimbria, visualized as the slice where the
temporal (inferior) horn of the lateral ventricle ascended into body of the
lateral ventricle in practice. After determining the sagittal coordinates for
anterior and posterior hippocampus, a member of the research team
(RPV) traced the hippocampal head and body in the corresponding coronal slices and determined sagittal and coronal coordinates by calculating the center of gravity of the tracings (Supplementary Figure 1;
reliability estimates in Supplementary Table 2). We based all other
memory system regions of interest on prior coordinates in extant literature (Supplementary Table 1). ROI coordinate selection criteria from
manuscripts included: 1) suggested involvement of the region in putative
anterior or posterior memory systems per Ranganath and Ritchey (2012),
and 2) demonstrated functional connectivity to other memory system
regions of interest. The tal2icbm tool transformed coordinates originally
defined in Talairach to Montreal Neurological Institute space (Lancaster
et al., 2007).
Functional connectivity analysis usually involves linear transformation of images to standard space, and signal extraction at specific
coordinates. However, individual variability in brain region size and
location may remain after transformation. Because of remnant variability, standard space coordinates did not cover the intended regions for
some brains in our dataset. Thus, to ensure correct brain region signal
extraction, a semi-automated method determined native space coordinates for non-hippocampal regions. For each participant, we transformed coordinates to T1-weighted structural space for visual inspection.
If the coordinate was not in the target region after inspection, raters
(RPV, PJP, ZJF) moved it the minimal amount necessary to an accurate
location. We defined target locations in consultation with atlases (Nolte,
2013; Woolsey et al., 2017). Manual correction procedures are detailed
in Supplementary Figures 2-9.
After confirming that coordinates were within desired areas, we
generated spherical regions of interest with 6-mm diameters. We then
masked the spheres with binarized gray matter segmentation images
calculated with the FSL Automated Segmentation Tool (Zhang et al.,
2001). Next, we transferred regions from structural to resting-state
functional space with the FSL Linear Image Registration Tool (Jenkinson et al., 2002). Resting-state time course extraction followed. We
extracted signal from combined left and right regions to form bilateral
regions of interest for region-to-region connectivity analysis when
appropriate (midline structures did not have left and right ROIs). We then
calculated Fisher Z transformed Pearson's r correlations for each
connection of interest in native functional space.
2.3. Magnetic resonance imaging data collection
The Detroit scanner was a 3 T Siemens Magnetom Verio full-body
magnet (Siemens Medical AG, Erlangen, Germany) with a 32-channel
head coil, located at the Wayne State University Magnetic Resonance
Research Facility. Participant scanning in the Netherlands occurred at the
Leiden Institute for Brain and Cognition on a 3 T Philips Achieva TX
scanner with a 32-channel head coil (Philips Healthcare, Best, the
Netherlands).
2.3.1. T1-weighted structural images
Detroit parameters: 3D T1-weighted magnetization-prepared rapid
gradient-echo (MP-RAGE) sequence, 176 slices collected parallel to the
bicommissural line, repetition time (TR) ¼ 1680 ms, echo time
(TE) ¼ 3.51 ms, inversion time ¼ 900 ms, flip angle ¼ 9.0 , pixel bandwidth ¼ 180 Hz/pixel, GRAPPA acceleration factor PE ¼ 2, field of view
(FOV) ¼ 256 mm, matrix size ¼ 384 384, voxel size ¼ 0.7
0.7 1.3 mm.
Leiden parameters: 3D T1-weighted gradient echo sequence, 140
slices, TR ¼ 9.7 ms, TE ¼ 4.60 ms, flip angle ¼ 8.0 , FOV ¼ 224 mm, matrix size ¼ 256 256, voxel size ¼ 0.88 0.88 1.20 mm.
2.3.2. Resting-state functional images
Detroit parameters: T2*-weighted echo-planar imaging sequence, 37
slices parallel to bicommissural line, 200 image volumes, TR ¼ 2200 ms,
TE ¼ 30 ms, flip angle ¼ 80 , pixel bandwidth ¼ 2232 Hz/pixel, GRAPPA
acceleration factor PE ¼ 2, FOV ¼ 220 mm, matrix size ¼ 80 80, voxel
size ¼ 2.8 mm isotropic.
Leiden parameters: T2*-weighted echo-planar imaging sequence, 38
slices, 200 image volumes, TR ¼ 2200 ms, TE ¼ 30 ms, flip angle ¼ 80 ,
FOV ¼ 220 mm, matrix size ¼ 80 80, voxel size ¼ 2.75 mm isotropic
with a 0.275 mm slice gap in the transverse plane.
2.3.3. Diffusion weighted images
Detroit only: multi-band echo-planar imaging sequence, 84 axial slices with 2.00 mm thickness, TR ¼ 3500 ms, TE ¼ 87.0 ms, multi-band
acceleration factor ¼ 3, flip angle ¼ 90 , refocus flip angle ¼ 160 ,
FOV ¼ 200 mm,
pixel
bandwidth ¼ 1724 Hz/pixel,
echo
spacing ¼ 0.69 ms, GRAPPA acceleration factor ¼ 2, anterior to posterior
phase encoding, diffusion directions ¼ 96 (6 B0), b-values ¼ 1000 (30
directions) & 1800 (60 directions) s/mm2, matrix size ¼ 100 100,
voxel size ¼ 2.00 mm isotropic. We acquired all b-values and directions
in a single sequence.
2.4. Image processing
Image processing pipelines utilized FMRIB Software Library tools
(FSL 5.0.8; https://fsl.fmrib.ox.ac.uk; Jenkinson et al., 2012), Freesurfer
6.0 (http://surfer.nmr.mgh.harvard.edu/; (Dale et al., 1999; Fischl et al.,
1999), TRACULA (Yendiki et al., 2011), 3D Slicer (Pieper et al., 2004),
AMICO for neurite density maps (Daducci et al., 2015), and in-house
Python scripts.
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using the following thermocycling protocol: 95 C for 5 min and 40 cycles
of 95 C for 5 s and 60 C for 30 s. We determined APOE ε4 status for 81 of
the 83 participants.
2.4.3. Diffusion weighted image analysis
Diffusion images underwent motion and eddy current correction with
the FSL Eddy tool (Andersson and Sotiropoulos, 2016), adjusting B-vectors accordingly. Images then underwent affine registration to corresponding T1-weighted images and subsequent affine registration to 1 mm
isotropic Montreal Neurological Institute space. Automated tractography
requires these affine mappings; however, tract reconstruction and all
other analyses occurred in native space. Prior to tractography, Freesurfer
brain segmentation and parcellation reconstructed brain anatomy from
T1-weighted images (Dale et al., 1999). The automated Bayesian global
tractography algorithm in Freesurfer, Tracts Constrained By Underlying
Anatomy (TRACULA), automatically reconstructed and labeled major
white matter fiber tracts from the diffusion images, utilizing the “ball-and-stick” model of diffusion (Behrens et al., 2007), and anatomic
priors (Yendiki et al., 2011).
Thresholded according to default settings (20% the maximum probability value), posterior probability distribution maps for the left and
right parahippocampal cingulum, cingulate gyrus cingulum, and uncinate fiber tracts became native-space regions of interest (Fig. 1). After
determining regions, we used neurite orientation dispersion and density
imaging analysis (NODDI), as implemented in the AMICO python module, to obtain neurite density maps (Daducci et al., 2015; Zhang et al.,
2012). The NODDI tissue model compartmentalizes the diffusion signal
into supposed intracellular water, extracellular water, and free water.
Neurite density serves as interpretation of the fraction of signal compartmentalized to intracellular water. We extracted weighted means of
neurite density values for cingulum and uncinate tracts, as well as
weighted means for fractional anisotropy and mean diffusivity. Voxel
parameter estimates were weighted by the voxel's posterior probability of
tract membership prior to weighted mean calculations over regions of
interest. Voxels towards the center of a white matter fiber tract had
greater posterior probabilities, while voxels further from the center had
lower probability of tract membership. Thus, voxels closer to the
boundary of white and gray matter contributed less to the weighted
means, which limited the potential contribution of partial volume effects
to the results.
2.6. Statistical models
We used general linear models to evaluate the effects of subjective
memory complaint status on average system functional connectivity, as
well as connectivity between individual regions, while controlling for
age, sex, and test site. Models initially included all two-way interactions,
but these were dropped from the final models as they were not significant. We also used general linear models to evaluate the effects of SCD on
cingulum and uncinate neurite density, while controlling for age and sex.
Test-site was not a covariate for these models as diffusion data collection
occurred only in Detroit. Finally, we used general linear models to
evaluate the effects of SCD on Wechsler Memory Scale index and verbal
fluency scores while controlling for age, sex, test site, and a test site by
memory complaint status interaction. We evaluated the models with this
interaction included to confirm that there were no systematic group
differences across test sites in cognitive performance; but as we observed
no significant interactions (p > .15), we dropped them from the final
models to interpret the predictors as main effects. To examine all other
group differences on demographic or neuropsychological metrics we
used independent samples t-tests or Fisher's exact tests. We determined
significance by correcting for the number of models involved in an
analysis topic, dividing .05 by the number of models and then using the
resulting alpha level to test for coefficient significance as well as full
model significance. We evaluated average anterior and posterior memory
system connectivity models at the α ¼ 0.025 level. We then evaluated
region-to-region functional connectivity, correcting for each of the 42
specific connections measured, at α ¼ 0.001. We evaluated neurite density, fractional anisotropy and mean diffusivity each at α ¼ 0.008, correcting for each of the 6 tracts evaluated. Finally, we evaluated Wechsler
Memory Scale performance, correcting for the 5 memory indices, at
α ¼ 0.01. The α ¼ 0.05 level served as the cutoff for all other neuropsychological and demographic comparisons as they were not the main foci
of this analysis, and because we anticipated no systematic group differences for those variables.
2.5. Apolipoprotein E genotype
3. Results
DNA isolation from saliva was performed using the Qiagen EZ1
Advanced Nucleic Acid Purification System in conjunction with the EZ1
DNA Tissue Kit and the EZ1 DNA Tissue Card. The “High-throughput
DNA purification with the Qiagen BioRobot™ EZ1” (http://www.
dnagenotek.com/US/pdf/MK-AN-006.pdf), an in-house validated procedure, was followed. Apolipoprotein E (APOE) single nucleotide polymorphism (SNP) genotyping was performed for rs429358 and rs7412
using 5 μl of Kapa Probe Fast ABI Prism 2x qPCR Master Mix, 1 μl template DNA, 0.25 μl of 20x TaqMan SNP Genotyping Assays (Applied
Biosystems), and 1.25 μl molecular grade water. A CEPH and an in-house
control were run along with samples. Samples and controls were run on
an Applied Biosystems Quantstudio 12K Flex Real-Time PCR Instrument
3.1. Demographics and neuropsychological assessment
Participant demographics and cognitive results are in Table 1. Demographics for the subsample of participants in the diffusion analysis are
in Supplementary Table 5. There was no significant age difference,
t(81) ¼ 0.84, p ¼ .40, between participants with SCD (M ¼ 68.5,
SD ¼ 7.7) and controls (M ¼ 67.0, SD ¼ 8.8). There was also no difference
in sex distribution across SCD status, Fisher's exact test p ¼ .99, nor difference in the distribution of individuals with SCD across test sites
p ¼ .18. Participants with SCD did not differ in APOE ε4 prevalence
Fig. 1. Cartoon estimation of evaluated fiber tract regions of interest in neurite density analysis, as well as posterior probability distributions of cingulate gyrus
cingulum, parahippocampal cingulum, and uncinate fasciculus fiber tracts as determined by TRACULA over an FA map of an example subject.
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compared to those without, p ¼ .22.
Individuals with SCD had higher Geriatric Depression Scale scores,
t(80) ¼ 2.34, p ¼ .02; however, they were significantly more likely to
answer “Yes” to a question directly related to memory functioning (“Do
you feel you have more problems with memory than most?”), p < .001.
After removing this question, the difference between group distributions
was no longer significant, t(80) ¼ 1.73, p ¼ .09. Note that both groups
on average were not depressed clinically according to the scale (Yesavage
et al., 1983) and did not significantly differ on the Beck Depression Inventory t(80) ¼ 1.75, p ¼ .08. Furthermore, none of the participants
had a history of major depression. We observed no differences between
participants with SCD compared to controls on neuroticism
t(79) ¼ 0.64, p ¼ .52, or conscientiousness t(79) ¼ 1.04, p ¼ .30. Participants with SCD and controls differed neither on IQ measures,
t(73) ¼ 0.01, p ¼ .99, nor Mini-Mental State Examination Scores
t(79) ¼ 1.13, p ¼ .26.
Participants with SCD performed worse on the Wechsler Memory
Scale visual working memory index compared to controls (β ¼ 0.23,
p ¼ .01, controlling for age, sex, and test site, Supplementary Table 3).
SCD status did not significantly relate to other memory indices (Supplementary Table 3). Furthermore, older age associated with poorer
performance across all memory indices, and the sample from the
Netherlands had better performance across indices.
3.2. Functional connectivity
3.2.1. Average system connectivity
We observed lower average posterior memory system connectivity in
participants with SCD after including age, sex, and test site in the model,
and controlling for multiple comparisons (α ¼ 0.025). The full model was
significant, F(4, 78) ¼ 12.18, p < .001, with an R2 of 0.38. SCD status
accounted for 4.45% of the variance in average system connectivity,
β ¼ 0.22, p ¼ .02, with participants with SCD displaying lower average
connectivity. Older age was associated with lower average posterior
memory system functional connectivity at trend level, accounting for
3.92% of the variance, β ¼ 0.20, p ¼ .03. The impact of sex on the
model was not significant and accounted for 0.12% of the variance,
β ¼ 0.04, p ¼ .70. Test site accounted for 28.3% of the variance with
participants in Detroit displaying lower average connectivity, β ¼ 0.60,
p < .001 (Fig. 2).
Regarding the anterior memory system, the full model was significant, F(4, 78) ¼ 9.52, p < .001, with an R2 of 0.33. We found a trend
towards lower average anterior memory system functional connectivity
in participants with SCD, β ¼ 0.21, p ¼ .03, 4.3% of variance explained,
though this result did not survive multiple comparison correction. Age
accounted for 5.4% of the variance, with older adults exhibiting significantly lower functional connectivity, β ¼ 0.23, p ¼ .01. Again, sex did
not contribute significantly to the model, accounting for 0.11% of the
variance, β ¼ 0.04, p ¼ .72. Test site accounted for 22% of the variance,
with participants in Detroit displaying significantly lower connectivity,
β ¼ 0.53, p < .001.
Table 1
ƚ Cohen's D. ƚƚ Fisher's exact test. ƚƚƚ Beta coefficient from a standardized
regression model with age, sex, and test site as included covariates. * Significant
at 0.05. ** Significant after multiple comparison correction (Wechsler Memory
Scale only).
Age
SCD Distribution across
sites
Sex distribution across
SCD status
Mini Mental State
Examination
IQ
Memory Functioning
Questionnaire
Frequency of
Forgetting Inverted
Mean
Geriatric Depression
Scale
Geriatric Depression
Scale without
question 14
GDS 14 “Do you feel you
have more problems
with memory than
most?”
Beck Depression
Inventory II
Big Five Inventory
Neuroticism
Big Five Inventory
Conscientiousness
Wechsler Visual
Memory Index
Wechsler Auditory
Memory Index
Wechsler Visual
Working Memory
Index
Wechsler Immediate
Memory Index
Wechsler Delayed
Memory Index
Controls
SCD
Effect
Size
p
66.96 8.79
30 DET/18 LEI
68.51 7.66
16 DET/19 LEI
.19ƚ
1.11ƚƚ
.40
.18
29F/19M
22F/13M
.51ƚƚ
.99
ƚ
3.2.2. Region-to-region connectivity
Following the significant difference between groups in average posterior memory system connectivity, we explored group differences in
functional connectivity between individual posterior memory system
regions with post hoc general linear models. We did not evaluate regionto-region connectivity between anterior memory regions as we did not
observe a statistically significant effect of SCD on average anterior
memory system connectivity. Controlling for multiple comparisons
(α ¼ .001), we observed significantly lower connectivity between the
precuneus and retrosplenial cortex in participants with SCD, β ¼ 0.35,
p ¼ .001, 11.6% of variance explained (Fig. 2). Though, the full model
was not significant F(4, 78) ¼ 4.29, p ¼ .003, R2 ¼ 0.18. Age accounted
for 1.18% of variance, which was not significant, β ¼ 0.11, p ¼ .29;
furthermore, sex accounted for 0.35% of variance, which was not significant β ¼ 0.07, p ¼ .57. Test site accounted for 7.08% of variance, with
participants in Detroit displaying lower functional connectivity,
β ¼ 0.30, p ¼ .01; though this was not significant after correction.
.26
28.96 1.27
28.65 1.10
.25
104.42 15.51
2.63 .80
104.40 13.42
3.54 .88
<.01Ɨ
1.08Ɨ
.99
<.001*
3.42 3.97
5.38 3.44
-.52Ɨ
.02*
3.40 3.39
4.82 3.32
-.39Ɨ
.09
1 Yes/47 No
19 Yes/15 No
7.78ƗƗ
<.001*
4.87 5.37
6.91 4.53
-.39Ɨ
.08
18.12 5.71
18.88 4.68
-.14Ɨ
.52
Ɨ
3.2.3. Supplemental functional connectivity and visual working memory
follow-up analysis
Because of the observed differences in functional connectivity and
visual working memory performance between groups, we further
explored the relationship between average posterior memory system and
retrosplenial-precuneus functional connectivity, and visual working
memory performance for the full sample of participants, for the subsample of participants with SCD, and for the subsample of participants
without SCD (Supplementary Table 4). Our results did not reveal a significant association between our measures of functional connectivity and
visual working memory performance in the total sample or in the subsamples, controlling for age, sex, and test site.
.30
35.50 6.14
34.12 5.22
.23
.52 .13
.53 .12
-.04ƚƚƚ
.72
.59 .11
.57 .11
-.14ƚƚƚ
.15
.48 .14
.43 .12
-.23
ƚƚƚ
.60 .10
.60 .09
-.06ƚƚƚ
.56
.52 .13
.51 .10
-.07ƚƚƚ
.51
3.3. Diffusion parameters
.01**
We did not observe any differences between participants with and
without SCD on measures of neurite density, fractional anisotropy, or
mean diffusivity for cingulum and uncinate fiber bundles at either the
α ¼ 0.05 level or the multiple model correction level, α ¼ 0.008 (Supplementary Tables 6-8). Furthermore, no age or sex effects on neurite
560
R.P. Viviano et al.
NeuroImage 185 (2019) 556–564
Fig. 2. Top: Average posterior memory system functional connectivity for individuals with and without SCD. Middle: Anterior memory system functional connectivity
for individuals with and without SCD. Bottom: Functional connectivity between retrosplenial cortex and precuneus for individuals with and without SCD.
SCD remain unclear. In a supplemental follow-up analysis, we did not
observe correlations between memory performance and this connection
within the full sample, nor within the SCD group alone. Thus, task
functional imaging may be necessary to determine the cognitive implications of lower precuneus and retrosplenial connectivity in SCD.
Regardless of specific cognitive implications, this disrupted connectivity
at wakeful rest may underlie self-reporting of memory issues.
In addition to functional connectivity differences related to SCD status, we also observed age-related connectivity differences. Specifically,
we observed lower anterior memory system connectivity, and trend level
lower posterior system connectivity, that associated with older age. This
age-related lower connectivity in the anterior memory system appears to
corroborate previous longitudinal observation that anterior medial
temporal lobe connectivity is vulnerable to aging (Salami et al., 2016),
but seems to contrast cross sectional findings suggesting that the posterior hippocampus is more sensitive to aging than the anterior hippocampus (Damoiseaux et al., 2016). However, it is important to note that
these previous studies examined age-effects across the adult lifespan (age
range: 25–80 years and 18–78 years respectively), whereas here we
examined age-effects across older age (i.e. 50–85 years). Furthermore, in
our previous study, Damoiseaux et al. (2016), we evaluated anterior
hippocampal connectivity to default mode regions (i.e. posterior memory
system) and not regions specific to the anterior memory system, as was
done here.
We observed no associations between memory system functional
connectivity and sex, but did consistently observe a site difference, such
that average connectivity was lower in the Detroit sample compared to
the Leiden sample. Although sequences were almost identical, the
density, fractional anisotropy, or mean diffusivity were observed for the
fiber tracts of interest.
4. Discussion
Here, we observed lower average functional connectivity in participants with SCD compared to those without, within a putative posterior
memory system (Ranganath and Ritchey, 2012), which largely overlaps
with the default mode network. This result is similar to disrupted connectivity observed in Alzheimer's disease (Greicius et al., 2004; Koch
et al., 2012) and supports SCD as a pre-mild cognitive impairment stage
of Alzheimer's disease. Lower average posterior memory system
resting-state functional connectivity could indicate decreased information processing within this system that could influence self-report of
memory complaints. While implicated in episodic memory and future
planning, default mode network regions, e.g., precuneus, also have a role
in self-referential processing and theory of mind (Buckner et al., 2008;
Saxe and Kanwisher, 2003). Moreover, the precuneus exhibits distributed network connectivity and has core involvement in integration of
self-generated information and external input; and functional imaging
studies have determined that recruitment of the precuneus occurs during
memory retrieval and self-awareness functioning (Cavanna and Trimble,
2006). In the present analysis, we observed lower functional connectivity
between the precuneus and retrosplenial cortex, another important
episodic memory region (Vann et al., 2009). This disrupted connectivity
may relate to self-awareness of memory processing. Or, it could relate to
hippocampal-independent memory retrieval. The implications of lower
retrosplenial cortex to precuneus resting-state functional connectivity for
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resting-state fMRI at later time points prior to objective decline.
Regardless, the present results do corroborate the results from previous
analysis of posterior memory components in SCD (Yasuno et al., 2015),
and are similar to connectivity results observed in mild cognitive
impairment, Alzheimer's disease, and other preclinical dementia (e.g.,
PiB þ or APOE-ε4 carrier) studies (Das et al., 2015; Greicius et al., 2004;
Koch et al., 2012; Sheline et al., 2010a, 2010b; Zhang et al., 2009).
Unfortunately, many of these studies are similarly hindered by the limitations of cross-sectional designs. Therefore, future analyses should
track functional change in SCD over time and determine if intrinsic
functional connectivity changes associate with change in cognitive
performance.
scanners were different, which could have influenced functional connectivity globally. However, there are various other variables that could
have influenced overall connectivity differences, such as site differences
in hypertension, medication use, body-mass index, racial distribution etc.
Even though we did not anticipate any differences between groups on
cognitive measures, as by definition, individuals with SCD perform
within the normal range on neuropsychological assessment, we did
observe lower visual working memory performance in individuals with
SCD. The older adult battery of the Wechsler Memory Scale IV, which is
commonly assessed in individuals over 65, does not contain the visual
working memory index as there were floor issues during standardization
of the spatial addition task (Wechsler, 2009). For the present analysis, we
used the standard adult battery and did not encounter floor issues in our
sample for the component subtests of the visual working memory index.
It is possible that lower visual working memory performance represents
executive functioning deficits in SCD as the spatial addition and symbol
span subtests that comprise the index require complex mental manipulations of information and discounting of irrelevant stimuli. These manipulations are cognitively demanding, and would recruit the central
executive component of the Baddeley working memory model (Baddeley,
2012). As groups did not differ on the visual or immediate memory
indices, but did differ on the visual working memory index, the locus of
subjective memory complaint related deficit may be within this central
executive component. Executive functioning deficit in SCD would relate
to an executive component deficit interpretation of Alzheimer's and mild
cognitive impairment-related working memory deficits (Huntley and
Howard, 2010; Morris and Kopelman, 1986). Our results indicate that
challenging visual working memory tests, such as those included in the
adult battery of the Wechsler Memory Scale IV, may be sensitive to early
cognitive decline. Therefore, inclusion of such tests in clinical assessments should be considered.
In contrast to previously observed white matter fiber tract diffusion
parameter differences between healthy older adults with and without
SCD (Hong et al., 2015; Li et al., 2016; Selnes et al., 2012, 2013; Yasuno
et al., 2015), we did not observe differences between groups in neurite
density, fractional anisotropy, or mean diffusivity. Possible reasons for
discrepancy across samples could include different operational definitions of subjective decline across studies and differences in other various
factors (e.g., medication non-compliance, blood pressure, scanner differences). It is unclear if functional disruption is more sensitive to detect
SCD than diffusion parameters; power for our diffusion analyses was
lower than for the functional connectivity analyses as there were fewer
participants, so we must temper our interpretations of the results of the
two modalities in tandem. Regardless, longitudinal analysis could
determine if changes in white matter diffusion characteristics follow, or
occur in conjunction with, functional brain changes and relate to progression of SCD to objective decline.
A limitation of our functional connectivity analysis was the multisite/multi-scanner approach. Differences in field heterogeneities and
measurement due to site, scanner vendor, and head coil may have
influenced site biases for connectivity patterns. Regardless, as there was
no difference in the distribution of participants with SCD across sites, and
because we controlled for variance related to test site in all our models, it
is unlikely that potential issues related to utilizing two scanners from
different vendors explain the SCD results. Furthermore, there were no
significant interactions between test site and SCD status for any of our
analyses, suggesting that systematic site differences do not explain our
results. Nevertheless, scanner/site differences were a major source of
nuisance variance.
The present analysis is also limited by its cross-sectional approach.
Although lower average memory system connectivity was observed at
our measurement in adults with SCD, it is possible this lower connectivity
might not capture the trajectory of functional connectivity change as
subjective impairment progresses to objective decline. Lower connectivity in our sample could have occurred due to cohort effects, and
memory system regions may exhibit increased functional coupling in
5. Conclusion
We observed lower posterior memory region functional connectivity
in SCD, which is similar to previous findings of disrupted connectivity in
Alzheimer's disease. Participants with SCD also had poorer visual working memory performance. Our results support SCD as a potential incipient dementia marker. Regardless, longitudinal research must
substantiate this claim.
Funding
This work was supported by the Netherlands Organisation for Scientific Research [Veni grant: 016.136.072].
Conflicts of interest
There are no actual or potential conflicts of interest for any of the
authors. None of the author's institutions have contracts relating to the
research through which they, or any other organisation, may stand to
gain financially now or in the future. There are no other agreements of
authors or their institutions that could be seen as involving a financial
interest in this work. As listed in the acknowledgments of the manuscript,
this work was supported by the Netherlands Organisation for Scientific
Research [Veni grant: 016.136.072] to Jessica S. Damoiseaux. The data
contained in this manuscript have not been previously published, have
not been submitted elsewhere, and will not be submitted elsewhere while
under consideration at Neuroimage. As listed in the manuscript, all
participants provided written informed consent as approved by local
ethics committee. All authors have reviewed the manuscript, approve of
its contents, and validate the accuracy of the data.
Acknowledgements
We would like to thank Pauline Croll and Gerda Labadie for help with
data collection at the Leiden University Medical Center.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.neuroimage.2018.10.015.
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