ARTICLES
Erin E. Sundermann,
PhD
Anat Biegon, PhD
Leah H. Rubin, PhD
Richard B. Lipton, MD
Wenzhu Mowrey, PhD
Susan Landau, PhD
Pauline M. Maki, PhD
For the Alzheimer’s
Disease Neuroimaging
Initiative
Correspondence to
Dr. Sundermann:
erin.sundermann@einstein.yu.edu
Better verbal memory in women than men
in MCI despite similar levels of
hippocampal atrophy
ABSTRACT
Objective: To examine sex differences in the relationship between clinical symptoms related to
Alzheimer disease (AD) (verbal memory deficits) and neurodegeneration (hippocampal volume/
intracranial volume ratio [HpVR]) across AD stages.
Methods: The sample included 379 healthy participants, 694 participants with amnestic mild
cognitive impairment (aMCI), and 235 participants with AD and dementia from the Alzheimer’s
Disease Neuroimaging Initiative who completed the Rey Auditory Verbal Learning Test (RAVLT).
Cross-sectional analyses were conducted using linear regression to examine the interaction
between sex and HpVR on RAVLT across and within diagnostic groups adjusting for age, education, and APOE e4 status.
Results: Across groups, there were significant sex 3 HpVR interactions for immediate and delayed
recall (p , 0.01). Women outperformed men among individuals with moderate to larger HpVR, but
not among individuals with smaller HpVR. In diagnosis-stratified analyses, the HpVR 3 sex interaction was significant in the aMCI group, but not in the control or AD dementia groups, for
immediate and delayed recall (p , 0.01). Among controls, women outperformed men on both
outcomes irrespective of HpVR (p , 0.001). In AD dementia, better RAVLT performance was
independently associated with female sex (immediate, p 5 0.04) and larger HpVR (delayed, p 5
0.001).
Conclusion: Women showed an advantage in verbal memory despite evidence of moderate hippocampal atrophy. This advantage may represent a sex-specific form of cognitive reserve delaying
verbal memory decline until more advanced disease stages. Neurology® 2016;86:1368–1376
GLOSSARY
AD 5 Alzheimer disease; ADNI 5 Alzheimer’s Disease Neuroimaging Initiative; aMCI 5 amnestic mild cognitive impairment;
CDR 5 Clinical Dementia Rating; HpVR 5 hippocampal volume/intracranial volume ratio; MCI 5 mild cognitive impairment;
MMSE 5 Mini-Mental State Examination; RAVLT 5 Rey Auditory Verbal Learning Test.
Editorial, page 1364
Supplemental data
at Neurology.org
The cognitive reserve theory posits that favorable premorbid factors including higher education
and IQ delay the onset of clinical deficits despite Alzheimer disease (AD)–related neurodegeneration because compensatory mechanisms are more readily engaged (e.g., alternate brain networks or cognitive strategies).1–3 The theory predicts that the onset of accelerated cognitive
decline is closer in time to AD dementia diagnosis in individuals with greater cognitive reserve;
however, after onset, their decline is more rapid because neurodegeneration is more advanced at
that point.4–6
Throughout life, women outperform men on verbal memory tasks.7–9 We predict that this
female advantage may reflect a sex-specific form of cognitive reserve resulting in a delay in the
clinical manifestation of memory impairment until more advanced neurodegeneration overwhelms the female advantage and decline begins. Thereafter, we predict that women decline
From the Einstein Aging Study and the Department of Neurology (E.E.S., R.B.L.) and the Department of Epidemiology and Population Health
(W.M.), Albert Einstein College of Medicine, Bronx; Department of Neurology (A.B.), State University of New York, Stony Brook; Department of
Psychiatry (L.H.R., P.M.M.), University of Illinois at Chicago; and Helen Wills Neuroscience Institute (S.L.), University of California, Berkeley.
Coinvestigators are listed on the Neurology® Web site at Neurology.org.
Data used in this study were obtained from the Alzheimer’s Disease Neuroimaging Initiative (ADNI) database (adni.loni.ucla.edu). Hence, with the
exception of Susan Landau, investigators within the ADNI contributed to the design and implementation of ADNI and/or provided data but did
not participate in analysis or preparation of this manuscript.
Go to Neurology.org for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article.
1368
© 2016 American Academy of Neurology
ª 2016 American Academy of Neurology. Unauthorized reproduction of this article is prohibited.
more rapidly than men due to greater pathologic burden. This sex difference is important
clinically because verbal memory deficits are
used to diagnose amnestic mild cognitive
impairment (aMCI) and AD dementia and
norms for clinical tests are currently not sexadjusted. A true aMCI diagnosis may be delayed more often in women than men because
the female advantage in verbal memory may
mask underlying neurodegeneration, particularly in earlier disease stages.
The hippocampus mediates verbal memory10–12 and hippocampal volume is related
to risk of aMCI13 and AD dementia.14 We
tested the hypothesis that the female advantage in verbal memory reflects a form of cognitive reserve by examining sex differences in
the relationship between AD-related clinical
presentation (verbal memory performance)
and neurodegeneration (hippocampal volume/intracranial volume ratio [HpVR]) across
and within diagnostic categories (control,
aMCI, AD dementia). We hypothesized that
the magnitude of the female advantage in verbal memory will vary by HpVR; the female
advantage will be evident among individuals
with moderate-to-large HpVR but not among
individuals with smaller HpVR.
METHODS Participants and data source. Cross-sectional
data were extracted from the Alzheimer’s Disease Neuroimaging
Initiative (ADNI) database (adni.loni.usc.edu) in June 2014.
ADNI has been previously described in detail at www.adniinfo.org. Since 2003, ADNI has recruited over 1,500 older
adults over 3 phases (ADNI-1, ADNI-GO, ADNI-2) from
over 50 sites in the United States and Canada. ADNI
participants are aged 55–90 years and fall within the
diagnostic categories of normal, early or late mild cognitive
impairment (MCI), and early AD dementia, with MCI
being the major target population. Study visits involve imaging,
neuropsychological, and clinical assessments. Recruitment
procedures for ADNI have been reported15 (www.loni.usc.edu/
ADNI), and ADNI eligibility criteria are described at www.adniinfo.org/Scientists/ADNIStudyProcedures.html.
Our sample included participants who had concurrent diagnostic, hippocampal volumetric, and verbal memory data available
from one visit cycle (n 5 1,384). Exclusionary criteria specific to
our study included missing covariate data (62 missing APOE e
genotype), presence of a significant medical condition that could
cause difficulty with protocol compliance (n 5 2), evidence of brain
infection, infarction, or other focal lesions at the participant’s
screening/baseline MRI (n 5 9), and a MCI diagnosis that did
not meet standard criteria for aMCI including objective memory
impairment and a subjective memory complaint (n 5 3).16
Standard protocol approvals, registrations, and patient
consents. ADNI was approved by the institutional review board
at each site and was compliant with the Health Insurance Portability and Accountability Act. All participants provided written
consent.
Neuropsychological outcomes. Participants underwent clinical and cognitive evaluations at each ADNI visit. The cognitive
evaluation included the following: (1) Mini-Mental State
Examination (MMSE)17 to assess global cognitive function,
(2) Clinical Dementia Rating (CDR)18 to assess dementia
severity, and (3) American National Adult Reading Test19 to
assess premorbid intelligence. The Rey Auditory Verbal
Learning Test (RAVLT),20 a multitrial list learning and
memory test that shows a female advantage,21 served as our
measure of verbal episodic memory. On each of 5 successive
trials, a list of 15 unrelated words was read aloud, and the
participant was instructed to recall aloud as many words as
possible (immediate recall score, range 0–75). A new list of
15 words (interference list) unrelated to the first list and to
each other was then read aloud, and the participant was
instructed to recall aloud as many words as possible. The
participant was then, again, asked to recall the first word list.
After a 30-minute delay in which other nonverbal tasks were
administered, the participant was again instructed to recall as
many words as possible from the first list (delayed recall score,
range 0–15). The primary outcome measures were immediate
and delayed recall scores.
Diagnostic criteria. Diagnostic criteria for an early AD
dementia diagnosis in ADNI included a MMSE score between
20 and 26, a CDR of 0.5 or 1, and meeting the National Institute of Neurological and Communicative Disorders and
Stroke–Alzheimer’s Disease and Related Disorders Association22 criteria for probable AD.15 Diagnostic criteria for an
aMCI diagnosis included MMSE score between 24 and 30,
CDR of 0.5, a subjective memory complaint, and objective
memory loss as measured by education-adjusted scores on the
Wechsler Memory Scale Logical Memory II, but without
significant impairment in other cognitive domains or
interference in daily life activities.15 The distinction of early
vs late aMCI is based on a modest vs advanced impairment of
the delayed recall portion of Logical Memory II.23 Classification
as normal required a MMSE score between 24 and 30 and a
CDR of 0.15
MRI acquisition. Structural MRI scans were collected on a
1.5T scanner based on a standardized protocol that was validated
across sites.24 High-resolution, T1-weighted volumetric
magnetization-prepared rapid gradient echo sequences were
collected in the sagittal plane, and T2-weighted fast-spin echo
sequences were collected in the axial plane.24 Prior to data
collection, customized imaging sequences were developed and
validated on phantoms and on 137 participants. Additionally, a
phantom scan was acquired for each participant and was centrally
evaluated for an optimal signal-to-noise ratio. Validation
procedures have been described24 (www.loni.usc.edu/ADNI).
Hippocampal volumetric MRI measures. Hippocampal volume data were analyzed using FreeSurfer v4.3 (UCSF–FreeSurfer
Methods, version 2012-12-11, ida.loni.usc.edu/pages/access/
studyData.jsp). Semiautomated hippocampal volumetry was
conducted using a previously validated high-dimensional brain
mapping tool (Medtronic Surgical Navigation Technologies,
Louisville, CO), which demonstrated similarity to manual
hippocampal tracing.25 To measure hippocampal volume, 22
control points were placed manually on individual brain MRI to
indicate hippocampal landmarks including the hippocampal head,
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Table 1
Overall sample characteristics by sex
Parameters
Women (n 5 579)
Men (n 5 729)
Age, y
72.6 (7.2)
73.9 (7.0)
0.001
Education, y
15.3 (2.8)
16.3 (2.8)
,0.001
Race, % Caucasian
91.9
94.8
0.03
APOE4 carrier, %
48.4
48.4
0.87
Premorbid intelligence
(no. ANART errors)
11.9 (9.3)
12.8 (9.5)
0.28
Global cognition (MMSE)
27.3 (2.7)
27.1 (2.6)
0.48
CDR-SOB
1.6 (1.8)
1.6 (1.6)
0.86
RAVLT immediate recall
38.1 (12.8)
32.7 (11.4)
,0.001
RAVLT delayed recall
5.1 (4.6)
3.8 (3.9)
,0.001
Hippocampal volume, mm3
6,528.3 (1,192.5)
6,878.1 (1,186.5)
,0.001
4.59 (0.03)
4.27 (0.03)
,0.001
a
HpVR
p Value
Abbreviations: ANART 5 American National Adult Reading Test; CDR-SOB 5 Clinical
Dementia Rating Sum of Boxes; HpVR 5 hippocampal volume/intracranial volume ratio;
MMSE 5 Mini-Mental State Examination; RAVLT 5 Rey Auditory Verbal Learning Test.
Data are presented as mean (SD) unless otherwise specified.
a
Hippocampal/intracranial volume 3 103.
tail, and at the superior, inferior, medial, and lateral boundaries on
5 equally spaced slices perpendicular to the long axis of the
hippocampus.26 Individual brain scans were then fitted to a
template brain using fluid image transformation.26 Hippocampal
volume was then measured by counting the pixels that
corresponded to the hippocampus. This hippocampal volumetry
protocol has demonstrated reliability with an intraclass coefficient
greater than 0.94.25 The right and left hippocampi were initially
examined individually; however, because the predictive value of
right vs left hippocampi was similar, we used the bilateral
measure. In order to control for sex differences in head size, the
HpVR was calculated using the formula hippocampal/intracranial
volume 3 103. Thus, HpVR represents a proportional, regional,
gray matter volume.
Statistical analysis. Participant characteristics (sociodemographic and clinical outcomes) and variables of interest
(RAVLT scores and HpVR) were compared between sexes in
the overall sample and within each diagnostic group using analyses of variance for continuous variables and x2 tests for categorical variables. We ran a multivariable linear regression across
diagnostic groups for each RAVLT outcome (immediate and
delayed recall) in order to examine the independent and interactive associations of sex and HpVR on verbal memory performance. The first model examined the independent effects of sex
and HpVR. The HpVR interaction term was added to the second model, but was eliminated if nonsignificant (p . 0.05).
The covariates included age, education, APOE genotype, and
diagnosis. APOE genotype was dichotomized by e4 allele carrier
status: APOE4 carriers and noncarriers. Secondary analyses
examined the independent and interactive associations of sex
and HpVR on RAVLT immediate and delayed recall within
diagnostic group using the same approach.
The sample comprised 1,308 participants including 379 controls,
694 individuals with aMCI (269 early MCI, 507 late
MCI), and 235 individuals with AD dementia (tables
RESULTS Sample characteristics.
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Neurology 86
1 and 2). The majority of the participants were from
ADNI 1 (n 5 756) and 2 (n 5 588) phases while 114
participants were from ADNI GO. Overall, across
diagnostic groups, women were younger, less educated, and less likely to be white compared to men
(p , 0.05). Race did not significantly relate to verbal
memory scores (p . 0.05) and, therefore, was not
included as a covariate. A comparison of men and
women within diagnostic group separately demonstrated that women were less educated compared to
men in each group (p , 0.001) and that women were
significantly younger than men in the aMCI group
only (p , 0.001). In the overall sample and within
each diagnostic group, immediate recall scores were
higher in women compared to men (p , 0.05). Delayed recall scores were higher in women compared to
men in the overall sample and within control and
aMCI subgroups (p , 0.001), but not the AD
dementia subgroup. Although absolute hippocampal
volumes were significantly larger in men compared to
women in the overall sample and in each diagnostic
group, the HpVR was significantly larger in women
compared to men (p , 0.05).
Linear regression results. The hypothesis that the magnitude of the female advantage in verbal memory
would vary by HpVR was supported by the finding
of a significant sex 3 HpVR interaction for both
immediate (p 5 0.001) and delayed recall on the
RAVLT (p 5 0.008; table 3). The magnitude of
the positive association between HpVR and RAVLT
performance was stronger in women compared to
men for immediate (B [unstandardized coefficient] 5
3.89, b [standardized coefficient] 5 0.26, SE 5 0.63,
p , 0.001 for women vs B 5 1.84, b 5 0.12, SE 5
0.49, p , 0.001 for men) and delayed (B 5 1.64, b 5
0.32, SE 5 0.23, p , 0.001 for women vs B 5 1.03,
b 5 0.19, SE 5 0.18, p , 0.001 for men) recall.
Figures 1A and 2A show this relationship demonstrating that women with larger HpVR (higher end of
HpVR linear spectrum) significantly outperformed
men with larger HpVR on immediate (figure 1A)
and delayed (figure 2A) recall, but this sex difference
was absent among individuals with smaller HpVR.
In diagnosis-stratified analyses, the HpVR 3 sex
interaction was significant in the aMCI group, but
not the AD dementia or control group. Specifically,
there was a HpVR 3 sex interaction for immediate
(p 5 0.0008) and delayed (p 5 0.006) recall in the
aMCI group. Similar to the results in the overall
sample, the association between HpVR and RAVLT
performance was stronger in women compared to
men for immediate (B 5 5.71, b 5 0.42, SE 5
0.70, p , 0.0001 for women vs B 5 2.69, b 5
0.20, SE 5 0.63, p , 0.001 for men) and delayed
(B 5 2.40, b 5 0.26, SE 5 0.26, p , 0.0001 for
April 12, 2016
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Abbreviations: AD 5 Alzheimer disease; aMCI 5 amnestic mild cognitive impairment; ANART 5 American National Adult Reading Test; CDR-SOB 5 Clinical Dementia Rating Sum of Boxes; HpVR 5 hippocampal
volume/intracranial volume ratio; MMSE 5 Mini-Mental State Examination; RAVLT 5 Rey Auditory Verbal Learning Test.
Data are presented as mean (SD) unless otherwise specified.
a
Hippocampal/intracranial volume 3 103.
,0.001
0.01
3.63 (0.05)
5,930.7 (969.7)
,0.001
3.83 (0.06)
,0.001
4.60 (0.04)
6,881.5 (1,148.5)
,0.001
,0.001
4.70 (0.04)
7,539.9 (935.1)
7,175.2 (886.0)
HpVRa
Hippocampal volume, mm
3
5.04 (0.04)
6,549.8 (1,114.0)
4.27 (0.04)
5,429.9 (1,013.3)
0.84
0.7 (1.3)
,0.001
7.0 (4.0)
8.2 (3.6)
RAVLT delayed recall
,0.001
4.7 (4.5)
3.3 (3.3)
0.8 (1.7)
0.05
—
—
22.0 (6.7)
24.1 (8.2)
—
0.20
,0.001
31.6 (9.3)
32.9
37.3
—
37.5 (11.7)
42.3 (10.4)
47.0 (8.5)
RAVLT immediate recall
—
—
Early vs late aMCI diagnosis, %
,0.001
0.06
4.1 (1.6)
0.49
0.02 (0.8)
0.03 (0.7)
CDR-SOB
0.54
1.5 (0.8)
1.5 (0.9)
4.5 (1.6)
0.35
0.90
23.1 (2.0)
16.9 (9.7)
15.8 (10.2)
23.2 (2.2)
0.43
0.66
13.4 (9.7)
27.6 (1.8)
12.1 (9.2)
0.49
27.6 (1.9)
28.9 (1.2)
29.1 (1.1)
Global cognition (MMSE)
8.9 (7.2)
9.4 (8.1)
Premorbid intelligence (no. ANART errors)
0.12
0.47
76.3
69.0
0.79
51.2
52.3
23.8
30.5
APOE4 carrier, %
0.13
,0.001
0.04
96.1
15.8 (2.8)
14.5 (2.7)
90.6
0.83
,0.001
95.3
16.2 (2.9)
15.4 (2.8)
,0.001
94.6
93.1
88.7
Race, % Caucasian
16.9 (2.5)
15.6 (2.7)
Education, y
0.14
0.23
74.7 (7.6)
74.3 (7.8)
0.001
73.3 (7.2)
71.2 (7.7)
74.6 (6.0)
73.7 (5.4)
Age, y
0.10
p Value
Men (n 5 128)
Women (n 5 107)
Men (n 5 192)
Women (n 5 187)
Parameters
p Value
Women (n 5 285)
Men (n 5 409)
p Value
AD dementia (n 5 235)
aMCI (n 5 694)
Controls (n 5 379)
Sample characteristics by sex and diagnostic group
Table 2
women vs B 5 1.48, b 5 0.30, SE 5 0.23, p ,
0.001 for men) recall. Among individuals with aMCI
with larger HpVR, women outperformed men on
immediate (figure 1C) and delayed (figure 2C)
recall, but this sex difference was not evident among
individuals with aMCI with smaller HpVR (lower
end of HpVR linear spectrum). Conversely, the
HpVR 3 sex interaction was not significant in control or AD dementia groups (p . 0.05). Among
controls, women significantly outperformed men
in immediate and delayed recall irrespective of
HpVR (p 5 0.01) and HpVR was not significantly
associated with immediate (p 5 0.53) or delayed
recall (p 5 0.95) (figures 1B and 2B). Among patients with AD dementia, women significantly outperformed men in immediate (p 5 0.04) but not
delayed recall (p . 0.05). Regardless of sex, smaller
HpVR in AD dementia were significantly associated
with poorer delayed recall performance (p 5 0.001)
but did not reach statistical significance for immediate recall (p 5 0.10).
DISCUSSION We examined whether sex modifies
the relationship between verbal memory and HpVR.
Consistent with the broader scientific literature, we
found that, compared to men, women performed better on immediate and delayed measures of verbal
memory7–9 and had larger HpVR.27 In the first study
to examine how sex modifies the relationship between
verbal memory and hippocampal volume, we found
overall that the female advantage in verbal memory
was apparent among individuals with moderate to
large HpVR but the advantage was absent among
individuals with smaller HpVR. Results were driven
by the interaction between sex and HpVR in the
aMCI group, where females outperformed men when
volumes were moderate to large but not when HpVR
were small.
We hypothesized that in the AD dementia group,
there would be no female advantage in verbal memory and that there would be no association between
sex and HpVR on memory because of the greater loss
of hippocampal volume. As hypothesized, delayed
recall scores did not significantly differ between male
and female patients with AD dementia; however, a
floor effect limits interpretation. Counter to hypotheses, female patients with AD dementia outperformed
male patients with AD dementia in immediate recall
(p 5 0.04); however, the sex difference was smaller
compared to controls and aMCI groups (mean difference 5 2.1, 4.7, and 5.9, respectively). These results
suggest a diminution of the female advantage but not
an elimination. Others have also reported an elimination28 or even a reversal29 of the female advantage in
verbal memory in AD dementia. Smaller HpVR were
associated with poorer delayed recall performance and
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April 12, 2016
1371
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Table 3
Results of multivariable linear regression analyses modeling the independent and interactive effects of sex and HpVR on verbal
memory performance
Multivariable linear regression models
Model 1: No interactions in model
Model 2: Interaction included in
model, sex 3 HpVRa
HpVRa
Sex (male vs female)
B (SE)
p Value
Immediate recall
24.53 (0.53)
,0.0001
Delayed recall
20.91 (0.19)
,0.0001
Immediate recall
25.40 (1.02)
,0.0001
20.35 (0.87)
0.68
1.02 (1.55)
0.51
Delayed recall
21.39 (0.42)
0.001
20.04 (0.35)
0.90
0.22 (0.63)
0.72
Immediate recall
24.85 (0.73)
,0.0001
4.02 (0.50)
,0.0001
3.02 (0.89)
0.0008b
Delayed recall
20.95 (0.27)
,0.0001
1.88 (0.18)
,0.0001
0.92 (0.33)
0.006b
Immediate recall
22.18 (1.05)
0.04
1.26 (0.86)
0.10
1.24 (1.59)
0.44
Delayed recall
20.10 (0.20)
0.64
0.55 (0.17)
0.001
20.04 (0.31)
0.89
Sample/outcome
B (SE)
p Value
B (SE)
p Value
2.81 (0.39)
,0.0001
2.05 (0.63)
0.001b
1.32 (0.14)
,0.0001
0.61 (0.23)
0.008b
Overall sample
Controls
aMCI
AD dementia
Abbreviations: AD 5 Alzheimer disease; aMCI 5 amnestic mild cognitive impairment; B 5 unstandardized regression coefficient; HpVR 5 hippocampal
volume/intracranial volume ratio.
All analyses were adjusted for age, education, APOE status, and diagnostic group (overall sample only).
a
Hippocampal/intracranial volume 3 103.
b
Significant.
trended towards an association with immediate recall
(p 5 0.10) among patients with AD dementia.
Among controls, women showed an advantage in
verbal memory over men and had larger HpVR, but
memory performance was unrelated to HpVR. The
lack of a relationship between hippocampal volume
and memory performance in healthy older adults
has been demonstrated previously,30 and may be
due to a limited range of variability among controls
compared to the aMCI or AD dementia group (SD 5
928, 1,146, and 1,019, respectively) or because of the
low prevalence in controls of AD-specific mechanisms underlying both hippocampal atrophy and
memory deficits. In controls, it is presumed that there
is a smaller degree of neurodegeneration and less reliance on reserves to maintain normal performance.
Therefore, differences in cognitive reserve among
controls are likely latent; however, an effect might
be detectable in a larger control group. One interpretation of these findings is that the reliable female
advantage in verbal memory may represent a greater
cognitive reserve in women in the domain of verbal
memory. The cognitive reserve theory posits that high
levels of certain premorbid factors such as IQ, education, and occupational attainment confer an advantage in the ability to compensate for neuropathologic
changes by, for example, engaging alternative brain
networks or cognitive strategies.1–3 The theory was
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Neurology 86
originally proposed to explain why individuals vary
in clinical presentation of AD yet have a similar
degree of neurodegeneration.1 In this way, women’s
high premorbid performance on verbal memory tests
might confer an advantage in the ability to maintain
verbal memory performance despite loss of hippocampal volume. In support of the theory that the
female advantage in verbal memory may reflect a
domain-specific cognitive reserve, a study found that,
among healthy adults, men show an earlier decline in
verbal memory compared to women.31 The current
study more directly demonstrates that the female
advantage is maintained despite moderate levels of
neurodegeneration. Furthermore, our results suggest
that the clinical manifestation of verbal memory
impairment is delayed until a more advanced level
of neurodegeneration in women vs men. Indeed,
using a standardized cutoff for impairment on the
RAVLT,32,33 women in the current study reached
the cutoff of impairment at a smaller HpVR than
men for both immediate (5 vs 6, respectively; figure
1A) and delayed recall (7.5 and ;8.5, respectively).
Thus, impairment in verbal memory was evident at a
smaller HpVR in women compared to men.
Our results might help to explain the paradoxical
sex differences in the incidence of aMCI vs AD
dementia. Some,34,35 but not all studies,36,37 reported that incidence of AD dementia is higher in
April 12, 2016
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Figure 1
Relationship between hippocampal volume/intracranial volume ratio (HpVR) and Rey Auditory Verbal
Learning Test (RAVLT) immediate recall scores in men and women
RAVLT immediate recall scores as a function of HpVR (hippocampal/intracranial volume 3 103) and sex in the (A) overall
group, (B) controls, (C) amnestic mild cognitive impairment (aMCI), and (D) Alzheimer disease (AD) dementia. b 5 sex-specific
standardized regression coefficient of the relationship between RAVLT scores and HpVR controlling for age, education,
APOE4, and diagnosis (overall sample only); HpVR 5 hippocampal/intracranial volume 3 103.
women, whereas incidence of MCI has been reported to be higher in men.38,39 In the present
cross-sectional study, there was a higher proportion
of aMCI diagnoses in men vs women (56.8% vs
48.5%, p , 0.002), but a nonsignificant higher
proportion of AD dementia diagnoses in women
vs men (19.7% vs 17.8%, p 5 0.08%). One possible explanation for this apparent paradox is that
verbal memory deficits are central in diagnosing
aMCI, and cognitive reserve in that domain may
mask a true aMCI diagnosis in women. Furthermore, a delayed onset of verbal memory impairment
in women and accelerated decline thereafter would
lead to a shorter window of time for an aMCI
diagnosis in women that may not be captured in
longitudinal assessments given at 12- to 24-month
intervals.
Our study has limitations. With a cross-sectional
design, the temporal relationship between verbal
memory and HpVR cannot be determined. However,
hippocampal volumes are a biomarker of imminent
cognitive decline and progression from MCI to AD
dementia in longitudinal studies.12,13 This design also
limits our test of the cognitive reserve theory because
we were unable to measure rates of decline in men vs
women. Population-based, longitudinal analyses are
needed to more definitively test the theory that the
female advantage in verbal memory may serve as a
form of cognitive reserve. The control and AD
dementia groups were smaller than the MCI group,
thereby limiting statistical power to detect a sex by
HpVR interaction within these groups; however, no
trend for an interaction was evident in the control and
AD dementia groups. The ADNI cohort represents a
Neurology 86
April 12, 2016
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ª 2016 American Academy of Neurology. Unauthorized reproduction of this article is prohibited.
Figure 2
Relationship between hippocampal volume/intracranial volume ratio (HpVR) and Rey Auditory Verbal
Learning Test (RAVLT) delayed recall scores in men and women
RAVLT delayed recall scores as a function of HpVR (hippocampal/intracranial volume 3 103) and sex in the (A) overall group,
(B) controls, (C) amnestic mild cognitive impairment (aMCI), and (D) Alzheimer disease (AD) dementia. b 5 sex-specific
standardized regression coefficient of the relationship between RAVLT scores and HpVR controlling for age, education,
APOE4, and diagnosis (overall sample only); HpVR 5 hippocampal/intracranial volume 3 103.
convenience sample of volunteers and is, therefore,
susceptible to selection bias. Past use of hormone
therapy was not assessed in ADNI and, therefore,
not adjusted for because of the difficulty in acquiring
self-reported medication history from participants
with memory problems.
Our findings replicate previous findings that
women perform better on a verbal memory task
and have larger HpVR compared to men. The relationship between verbal memory and HpVR varies
by sex; women show an advantage in verbal memory
despite minimal to moderate levels of hippocampal
atrophy. Findings suggest that women might show
a sex-specific cognitive reserve in the domain of verbal
memory. If replicated, our findings suggest the need
to evaluate whether diagnosis of aMCI is made at a
later disease stage in women compared to men
1374
Neurology 86
because this sex-specific advantage in verbal memory
masks underlying neurodegeneration. If so, then sexbased norms in clinical memory tests might improve
diagnostic accuracy in women.
AUTHOR CONTRIBUTIONS
E.E.S., A.B., P.M.M.: study concept. E.E.S., A.B., P.M.M., R.B.L., L.H.R.,
W.M., S.L.: study design. E.E.S., S.L.: data acquisition. L.H.R., E.E.S.: statistical analysis. E.E.S., A.B., P.M.M., R.B.L., S.L.: data interpretation. E.E.S.:
initial manuscript preparation. All authors provided a critical review of manuscript for important intellectual content and contributed to and approved the
final manuscript.
ACKNOWLEDGMENT
The authors thank the ADNI study subjects and investigators for their
participation.
STUDY FUNDING
Data collection and sharing for this project was funded by the Alzheimer’s Disease Neuroimaging Initiative (ADNI) (NIH grant U01
April 12, 2016
ª 2016 American Academy of Neurology. Unauthorized reproduction of this article is prohibited.
AG024904). ADNI is funded by the National Institute on Aging, the
National Institute of Biomedical Imaging and Bioengineering, and
through contributions from nonprofit partners the Alzheimer’s Association and Alzheimer’s Drug Discovery Foundation, with participation
from the US Food and Drug Administration and from the following:
Abbott; Alzheimer’s Association; Alzheimer’s Drug Discovery Foundation; Amorfix Life Sciences Ltd.; AstraZeneca; Bayer HealthCare; BioClinica, Inc.; Biogen Idec Inc.; Bristol-Myers Squibb Company; Eisai
Inc.; Elan Pharmaceuticals Inc.; Eli Lilly and Company; F. HoffmannLa Roche Ltd. and its affiliated company Genentech, Inc.; GE
Healthcare; Innogenetics, N.V.; IXICO Ltd.; Janssen Alzheimer Immunotherapy Research and Development, LLC; Johnson and Johnson Pharmaceutical Research and Development LLC; Medpace, Inc.; Merck and
Co., Inc.; Meso Scale Diagnostics, LLC; Novartis Pharmaceuticals Corporation; Pfizer Inc.; Servier; Synarc Inc.; and Takeda Pharmaceutical
Company. Drs. Sundermann and Lipton’s time was supported by funding for the Einstein Aging Study: National Institute on Aging Grant
AG003949, AG026728, TL1RR000087, T32-GM007288, the Leonard
and Sylvia Marx Foundation, and the Czap Foundation.
DISCLOSURE
8.
9.
10.
11.
12.
13.
E. Sundermann, A. Biegon, and L. Rubin report no disclosures relevant
to the manuscript. R. Lipton reports research support from the NIH:
PO1 AG003949 (Program Director), PO1AG027734 (Project Leader),
RO1AG025119 (Investigator), RO1AG022374-06A2 (Investigator),
RO1AG034119
(Investigator),
RO1AG12101
(Investigator),
K23AG030857 (Mentor), K23NS0514090m1A1 (Mentor), and
K23NS47256 (Mentor), the National Headache Foundation, and the
Migraine Research Fund; serves on the editorial boards of Neurology®
and Cephalalgia and as senior advisor to Headache; has reviewed for the
NIA and NINDS; holds stock options in eNeura Therapeutics (a company without commercial products); and serves as consultant, advisory
board member, or has received honoraria from Alder, Allergan, American
Headache Society, Autonomic Technologies, Avanir, Boston Scientific,
Bristol Myers Squibb, Colucid, Dr. Reddy’s, Electrocore, Eli Lilly, Endo,
eNeura Therapeutics, Informa, Labrys, Merck, Novartis, Teva, and
Vedanta. W. Mowrey reports no disclosures relevant to the manuscript.
S. Landau has served as a paid consultant for Genentech, Synarc, Biogen,
and Janssen. P. Maki reports no disclosures relevant to the manuscript.
Go to Neurology.org for full disclosures.
18.
Received August 4, 2015. Accepted in final form October 26, 2015.
19.
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