Psychology
2012. Vol.3, Special Issue, 834-840
Published Online September 2012 in SciRes (http://www.SciRP.org/journal/psych) http://dx.doi.org/10.4236/psych.2012.329126
834
Resting EEG Activity and Ovarian Hormones as Predictors of
Depressive Symptoms in Postmenopausal Women without a
Diagnosis of Major Depression
Silvia Solís-Ortiz1, Elva Pérez-Luque1, Maria del Pilar Pacheco-Zavala2
1Departamento de Ciencias Médicas, División de Ciencias de la Salud, Campus León,
Universidad de Guanajuato, Guanajuato, México
2Instituto de Mexicano del Seguro Social UMF53 de León, Guanajuato, México
Received June 8th, 2012; revised July 17th, 2012; accepted August 16th, 2012
The aim of this study was to examine the effects of depressive symptoms on resting EEG and their corre-
lation with endogenous hormone levels in postmenopausal women without a diagnosis of major depress-
sion. Fifty postmenopausal women aged 48 to 60 years were assessed for depressive symptoms using the
Beck Depression Inventory. EEG activity was recorded during rest with eyes closed in 23 participants
with minimal and 27 with moderate depressive symptoms. Relative power for delta, theta, alpha1, alpha2,
beta1 and beta2 were analyzed and compared between women with minimal and moderate depressive
symptoms. Hormonal levels of estrone, estradiol, progesterone, follicle-stimulating hormone and lu-
teinizing hormone were obtained and correlated with the EEG parameters. The women with moderate de-
pressive symptoms showed more relative alpha1power (p = .01) and less relative beta 2 power (p = .03).
Relative theta and alpha2 power, estradiol levels and menopausal years were predictors of depressive
symptoms. Progesterone was negatively correlated with the theta band (p = .005) and positively correlated
with the beta2 band (p = .02) in women with moderate depressive symptoms. Estrone was negatively cor-
related with the alpha2 band (p = .05), and estradiol was positively correlated with the theta band (p = .02)
and negatively correlated with the beta2 band (p = .05) in women with minimal depressive symptoms.
These findings suggest that slow and fast EEG relative power, menopausal status and estrogen levels pre-
dict depressive symptoms and that progesterone is related with moderate depression.
Keywords: EEG; Estrogen; Progesterone; Depression; Postmenopause
Introduction
Many women experience depressive moods at the time of
natural menopause and early postmenopausal periods (Harlow
& Abraham, 1999; Soares, 2010; Bromberger & Kravitz, 2011).
In some women these symptoms range from mild to severe and
require treatment (Lebowitz, Pearson, & Schneider, 1997; Mac-
Queen & Chokka, 2004; Dennerstein & Soares, 2008), whereas
in other women, symptoms are minor or absent, perhaps repre-
senting the common depressive symptoms of a typical woman
in mid-life. Because depression coincides with the onset of na-
tural menopause and early postmenopausal periods, it has been
associated with ovarian hormones (Birkhauser, 2002; Studd &
Panay, 2004; Frey, Lord & Soares, 2008; Ryan et al., 2009),
particularly estrogens. The circulating level of estrogen in
women shows a very steep decline over the 12 months after
menopause, with elevated FSH (Meldrum, Davidson, Tataryn,
& Judd, 1981). Its decrease is associated with physiological
changes affecting mood, mental state and memory (Fink, Sum-
ner, Rosie, Grace & Quinn, 1996). Several studies have re-
ported that estrogens modulate serotonergic function and may
exert effects on mood (Rubinow, Schmidt, & Roca, 1998;
Lasiuk & Hegadoren, 2007; Soares & Zitek, 2008). Thus, fluc-
tuations in levels of estrogen have been correlated with emo-
tional changes in mid-life women. However, the relationship
between depressive symptoms and estrogen in menopause has
not been clear. Most studies have examined depressive scores
and their possible relation with sex hormones in menopausal or
postmenopausal women diagnosed with major depression. In
some cases, this approach has provided relevant information,
but in other cases, the findings are discrepant. Some correlation
studies of mood and hormone levels in menopause and post-
menopause have found no association or weak associations
(Birkhauser, 2002). Prospective studies have found the meno-
pausal transition to be a period of heightened risk for the de-
velopment of depressive symptoms or depression (Maartens,
Knottnerus, & Pop, 2002; Freeman et al., 2004; Woods et al.,
2008; Soares, 2010). One prospective study did not find sig-
nificant associations between depressive symptoms and abso-
lute values of sex hormones in postmenopausal women, but the
decline in estradiol was associated with increased risk of de-
pressive symptoms (Ryan et al., 2009).These inconsistent re-
sults seem to be at least partly due to methodological problems
and the fact that depressed mood cannot be equated with de-
pressive disorder (Saletu et al., 1996; Smith, 1996; Vesco, Ha-
ney, Humphrey, Fu, & Nelson, 2007). Therefore, the investiga-
tion of post-menopausal women without a diagnosis of major
depression and a focus on objective measures of brain function
and ovarian profile might provide additional information con-
cerning the manifestation of depressive symptoms.
Electroencephalographic (EEG) methods in the resting state
have been useful to assess brain function and depression be-

S. SOLÍS-ORTIZ ET AL.
cause EEG measurements differ between depressed individuals
and normal subjects (Saletu, 1993; Kwon, Youn & Jung, 1996;
Debener et al., 2000; Morgan et al., 2005; Herrington et al.,
2010). In patients with major depression have found increased
slow wave activity (Adler, Bramesfeld, & Jajcevic, 1999), in-
creased alpha and beta activity (Pollock & Schneider 1990),
more delta power (Morgan et al., 2005), increased delta, theta
and beta activity and decreased alpha activity (Begić et al.,
2011) and frontal asymmetry (Debener et al., 2000; Deslandes et
al., 2008). The EEG approach has also been applied to evaluate
menopausal women with major depression, although few stud-
ies are reported in the literature. The EEG maps of menopausal
women with a diagnosis of major depression show less total
power and absolute power in the delta, theta and beta band,
more relative delta and less alpha power than controls and sig-
nificant relationships between estradiol levels and EEG meas-
ures (Saletu et al., 1996; Saletu, Anderer, & Saletu-Zyhlarz, 2010).
However, depressive symptoms in postmenopausal women
without a diagnosis of major depression and their relation to
ovarian profile and EEG measures are not well understood. The
aim of the current study was to examine the effects of depres-
sive symptoms in postmenopausal women without major de-
pression on resting EEG measures and their relationship to
hormone levels of estradiol, estrone, FSH, LH and progesterone.
It was hypothesized that resting EEG would differ depending
on the intensity of depressive symptoms and would be related
to the hormonal profile. This approach will help to better un-
derstand postmenopausal depression and to implement strate-
gies of prevention and treatment in future research.
Method
Participants
A total of 136 women responded to recruitment advertise-
ments in a cross-sectional study. All respondents met the
DSM-IV (American Psychiatric Association, 2000) criteria for
a diagnosis of mood disorder or psychosis and ruled out major
depression. Of the 136 respondents, 50 postmenopausal women
volunteers between 48 and 60 years old with an intact uterus
met the criterion of no history of major depression and were
assessed for depressive symptoms. This sample size was calcu-
lated to yield an expected statistical power of .99 to detect a
10% difference in minimal and moderate depressive symptoms
with a two-sided significance level of α = .05. All women were
given a medical history interview to assess their health status.
To participate in the study, the women must have been amen-
orrheic for at least 12 months and had no history of cardiovas-
cular, head trauma, brain surgery, stroke, or metabolic, endo-
crinological or malignant diseases. None of the participants were
taking any type of medication at the time of the study or had
ever received hormonal treatment. Participants were tested in a
single session by one trained female (between 0900 h and 1100
h). Participants were instructed to abstain from caffeine, alcohol
and smoking and to sleep for 8 h on the day prior to testing.
This study was approved by the Ethics Committee of the De-
partment of Medical Sciences of the University of Guanajuato
for Research on Human Subjects, and is in accordance with the
Declaration of Helsinki. All subjects provided written informed
consent prior to participating in the study.
Mood Questionnaire
Depressive symptoms were evaluated through self-report us-
ing the Beck Depression Inventory (BDI) (Beck & Steer, 1993)
in a standardized version for the Mexican population (Jurado et
al., 1998) in the 50 women included in the study. This ques-
tionnaire consists of 21 items that measure current depressive
symptoms. Each item contains a group of four statements, from
which the subject chooses one according to how she felt in the
last week. Individual questions of the BDI assess mood, pessi-
mism, sense of failure, self-dissatisfaction, guilt, punishment,
self-dislike, self-accusation, suicidal ideas, crying, irritability,
social withdrawal, body image, work difficulties, insomnia,
fatigue, appetite, weight loss, bodily preoccupation, and loss of
libido. Items 1 to 13 assess symptoms that are psychological in
nature, while items 14 to 21 assess more physical symptoms.
The BDI has a reliability high (Cronbach’s alpha coefficient
of .85), meaning that the items on the inventory are highly cor-
related with each other. The BDI has concurrent validity in that
it tends to agree with other measures of depression (correlations
of .93 and .84). The total score is obtained by adding the scores
for the 21 items, with 0 as the lowest score and 64 as the
maximum score. Depressive scores were compared between
groups with minimal and moderate depressive symptoms.
EEG Recording
EEG activity was recorded between 0900 h and 1100 h dur-
ing rest with eyes closed. Twenty-two electrodes were placed
according to the 10 - 20 International System at F3, F4, F7, F8,
FC3, FC4, C3, C4, CP3, CP4, P3, P4, O1, O2, FT7, FT8, Fz,
FCz, Cz, CPz, Pz and Oz using a Quick Cap (model Neuro-
scan). The ipsilateral earlobes were used as a reference for
electrode placement. EEGs were recorded on a 40-channel
NuAmps model digital amplifier (Neuroscan) set to pass fre-
quencies from .5 to 35 Hz. EEG activity was recorded on a
personal computer at a sampling rate of 512 Hz and was ana-
lyzed off line. EEG activity was carefully inspected for eye
movement artifacts. Epochs with artifacts or signs of sleep were
discarded from the analyses. During recordings, participants
were instructed to relax comfortably in a chair and to place
their chin on an individually adjusted head-rest. This recording
session consisted of a 5 min period with eyes closed. A mini-
mum of 20 long artifact free epochs, each 2 seconds in length
(John & Prichep, 1980) were selected for further processing to
obtain the global relative power values for the following bands:
delta, .5 - 4.0 Hz; theta, 4.0 - 8.0 Hz; alpha1, 8.0 - 11.0 Hz; al-
pha2, 11.0 - 14.0 Hz; beta1, 14.0 - 25.0 Hz; and beta2, 25.0 -
35.0 Hz. The relative power values of each frequency band
were compared between groups with minimal and moderate
depressive symptoms.
Hormonal M easurements
A 10 mL blood sample was collected from participants. ELISA
was used to determine the 17 β-estradiol and progesterone lev-
els. Commercially available radioimmunoassay kits were used
to determine follicle-stimulating hormone (FSH), and luteiniz-
ing hormone (LH) levels. The serum hormone levels were used
to confirm the hormonal status of participants and to establish
relations with EEG variables.
Statistical Analysis
Statistical analyses were performed with STATISTICA for
Windows 8 (StatSoft, Inc). Before statistical procedures were
applied, the data were tested for normal distribution using

S. SOLÍS-ORTIZ ET AL.
Leveneʼs test. Studentʼs t-test was used to compare the demo-
graphic characteristics of the participants their depressive
symptoms scores. A Mann-Whitney U test was used to com-
pare the hormonal levels among participants with minimal and
moderate depressive symptoms. Studentʼs t-test was also used
to compare EEG variables of global relative power among par-
ticipants with minimal and moderate depressive symptoms. The
Spearman correlation test was used to correlate the variables of
EEG relative power to hormone levels and depressive symptom
scores. Hormonal variables were transformed to logarithms to
fit the normal distribution and to apply multivariate analysis. A
multiple regression analysis was used to assess the relative
contribution of depressive symptoms as an independent vari-
able, with demographic variables, hormone levels and EEG
relative power as independent variables. The Visual Statistics
System (ViSta) for Windows 7.9 module ¨Effect size¨ was used
to correct the data outlier and estimate the effect sizes. Effect
sizes are indicated by the coefficient (ρI) between minimal and
moderate depressive symptoms groups. The ρI values were
squared to ease interpretation in terms of the percentage of the
total variance associated with an effect. Significance was de-
fined as alpha levels of p < .05.
Results
Depressive Symptoms
Of the fifty participants included in the study, 23 scored be-
tween 0 and 9 on the Beck Depression Inventory and were con-
sidered the group with minimal depressive symptoms. In the
remaining group, 27 scored between 10 and 35 and were con-
sidered the group with moderate depressive symptoms. The
comparison of depressive symptoms between these two groups
was significant (t = 10.238, p = .0000001, ρI = .85, explaining
73.10% of the total variance in the data) (Figure 1). The par-
ticipants did not show scores of severe depressive symptoms.
Characteristics of Participants
The women with minimal and moderate depressive symptoms
did not differ significantly in age, schooling, menarche, menopausal
years, blood pressure, weight, height, body mass, pregnancies,
glucose, alcoholism and smoking (Table 1). The women with
minimal and moderate depressive symptoms did not differ sig-
nificantly in hormonal levels of FSH, LH, 17β-estradiol, and
Figure 1.
Shows minimal and moderate depressive scores obtained from the Beck
Depression Inventory. Asterisk on the bars indicate significant differ-
ences between groups (*p < .05).
progesterone. The hormonal profiles were within the expected
ranges for postmenopausal healthy women (Table 2).
Correlations between Depressive Symptoms and
Hormones
Table 3 shows the results of a Spearman rank correlations
analysis between depressive symptoms and hormone levels.
The correlation analysis showed that minimal depressive symptoms
did not correlate significantly with FSH, LH, progesterone, es-
trone and estradiol levels. Only moderate depresssive symptoms
were negatively correlated with estradiol (r = –.66, p < .05).
Table 1.
Demographic characteristics of postmenopausal women with minimal
and moderate depressive symptoms.
Minimal Depressive
Symptoms
(n = 23)
Moderate Depressive
Symptoms
(n = 27)
Characteristics
Mean ± SD Mean ± SD
t p
Age (years) 54 ± 4.0 51 ± 3.0 .889.11
Menarche
(years) 12 ± 1.0 13 ± 1.0 .958.35
Menopause (years)48 ± 3.9 46 ± 4.0 –1.244.22
Gestation (n) 3.0 ± 2.0 5.0 ± 3.0 1.761.11
Weight (Kg) 72 ± 13 68 ± 7.0 –.426.10
Size (m) 1.5 ± .10 1.5 ± .10 –.905.90
BMI (Kg/m2) 30 ± 5.0 30 ± 3.0 .111.91
SBP (mmHg) 113 ±11 107 ± 9.0 .335.40
DBP (mmHg) 69 ± 6.0 65 ± 5.0 .533.06
Glucose (mg/dL) 87 ± 12 65 ± 5.0 .860.06
Note: p values < .05 Student’s t test; BMI = Body Mass Index; SBP = Systolic
Blood Pressure; DBP = Diastolic Blood Pressure.
Table 2.
Serum hormone levels in postmenopausal women with minimal and
moderate depressive symptoms.
Minimal Depres-
sive Symptoms
(n = 23)
Moderate Depres-
sive Symptoms
(n = 27)
Hormones
Median (range) Median (range)
z p
FSH (mUI/mL) 31.0 (13.3 - 37.1) 28.0 (22.1 - 39.8)–.37.70
LH (mUi/mL) 44.4 (33.2 - 59.5) 51.9 (39.7 - 56.4)–.45.65
Progesterone (ng/mL).2 (.10 - .6) .40 (.1 - 1.0) –.80.42
Estrone (pg/mL) 8.2 (1.2 - 24.2) 23.8 (1.2 - 39.9) –.68.49
Estradiol (pg/mL) 11.9 (2.6 - 22.9) 10.1 (2.9 - 16.8) .38.71
Note: FSH = Follicle Stimulating Hormone; LH = Luteinizing Hormone; p values
< .05 Mann-Whitney U test.
Table 3.
Correlation between minimal and moderate depressive symptoms and
serum hormone levels.
Hormones Minimal Depressive
Symptoms
Moderate Depressive
Symptoms
FSH (mUI/mL) .29 .08
LH (mUI/mL) .37 –.12
Progesterone
(ng/mL) –.51 –.17
Estrone (pg/mL) –.11 –.20
Estradiol (pg/mL)–.21 –.66*
Note: *p < .05 Spearman Correlation test; FSH = Follicle Stimulating Hormone;
LH = Luteinizing Hormone.
836

S. SOLÍS-ORTIZ ET AL.
Global Relative Power postmenopausal women showed different indices of depressive
symptoms related to brain function measures and hormone
levels, which were predictors of depression. Beck scores from
The global relative power of the significant differences be-
tween the women with minimal and moderate depressive symp-
toms is shown in Figure 2. There were only significant differ-
ences between the groups for the alpha1 (p = .01) and beta2 (p
= .03) bands. The delta (p = .80), theta (p = .73), alpha2 (p
= .60), and beta1 (p = .30) bands did not show significant dif-
ferences between groups. Comparisons between groups showed
that the relative power of alpha1was significantly lower in the
group with minimal depressive symptoms and was highest in
the groups with moderate depressive symptoms. The relative
power of the beta2 band was significantly highest in the group
with minimal depressive symptoms and was lower in the group
with moderate depressive symptoms.
Table 4.
Correlation between EEG relative power bands and hormone levels in
postmenopausal women with minimal and moderate depressive symp-
toms.
Minimal Depressive Symptoms
Spectral Bands
Hormones
DeltaTheta Alpha1 Alpha2 Beta1Beta2
FSH (mUI/mL) .31 –.27 –.15 0.31 –.02.04
LH (mUi/mL) .33 .21 .05 –.12 –.43–.29
Progesterone (ng/mL).38 .5 .31 .15 –.59–.48
Estrone (pg/mL) .01 .57 .33 –.68* –.46–.41
Estradiol (pg/mL) .22 .68* .55 –.33 –0.47–.62*
Moderate Depressive Symptoms
FSH (mUI/mL) –.1 –.13 –.24 –.52 .34 .22
LH (mUi/mL) .05 –0.22 –.52 –.49 .41 .33
Progesterone (ng/mL).13 –.80** –.52 .01 .53 .68*
Estrone (pg/mL) –.06–.1 –.29 –.21 –.08.16
Estradiol (pg/mL) .79 –.39 –.44 .14 .14 .46
Correlations between Hormones and EEG Relative
Power
The results of correlations between hormone levels and rest-
ing-state EEG relative power are shown in Table 4. In women
with minimal depressive symptoms, estrone was negatively
correlated with the relative power of alpha2 band (r = –.68, p
= .03) and estradiol was positively correlated with the theta
band (r = .68, p = .02) and negatively correlated with the beta2
band (r = –62, p = .05). In women with moderate depressive
symptoms, progesterone was negatively correlated with the
relative power of the theta band (r = –.80, p = .005) and posi-
tively correlated with the beta2 band (r = .68, p = .02). Note: *p < .05, **p < .01 Spearman Correlation test.
Multiple Re gression Anal ysis Table 5.
Predictors of depressive symptoms in postmenopausal women.
The results of the multiple regression analysis performed
with both moderates and minimum depressive symptoms are
shown in Table 5. The analysis showed that the relative power
of the theta band, the alpha2 band, years of menopause and log
estradiol were included in the regression model, accounting for
14.57% of the variance.
Multiple Regression Model Adjusted
R2 = .1457
Depressive symptoms
β t
p
Theta –1.110 –2.407 .031*
Alpha2 –.956 –2.437 .029*
Menopause (years) .560 2.440 .029*
Log. Estradiol (pg/ml)–.811 –2.378 .032*
Discussion
The present findings confirmed the hypothesis that Note: *p < .05.
Figure 2.
Shows EEG relative power (%) for delta, theta, alpha1, alpha2, beta and beta 2 bands between
postmenopausal women with minimal and moderate depressive symptoms. Asterisks on the
bars indicate significant differences between groups (*p < .05).

S. SOLÍS-ORTIZ ET AL.
the participants ranked as minimal to moderate depressive
symptoms, and the significance between them was relevant.
This result explained 73.10% of the total variance. The partici-
pants’ characteristics were similar between the groups with
minimal and moderate depressive symptoms. Menopausal years
were confirmed as a significant predictor of depressive symp-
toms, explaining part of the variance in the multiple regression
analysis. These results partially coincide with other studies that
have investigated the relationship between menopause and
psychological symptoms, especially depression. Epidemiologi-
cal studies have found that the transition to menopause and its
changing hormonal milieu is strongly associated with new on-
set of depressed mood among women with no history of de-
pression (Freeman, Sammel, & Nelson, 2006). A prospective
study demonstrated that women with a history of depression are
nearly five times more likely to have a diagnosis of major de-
pression during the menopausal transition, whereas women
with no history of depression are two to four times more likely
to report depressed mood compared with premenopausal wo-
men (Freeman, 2010). It has also been reported that the risk of
experiencing a major depressive episode is greater for women
aged 42 - 52 years during the peri-menopausal or early post-
menopausal periods than when they were pre-menopausal
(Bromberger et al., 2011).
Depressive symptoms analyzed in the current study showed
significant correlations between hormone levels of estrogen and
progesterone and EEG relative power. Postmenopausal women
with moderate depressive symptoms exhibited more relative
alpha1 power (the slow component of the alpha band) and less
relative beta2 power (fast activity) compared with the group
with minimal depressive symptoms, suggesting decreased brain
electrical activity. Several brain function studies have revealed
important relations between depressive mood and EEG studies,
supporting the current findings. Increased alpha or theta power
has been observed in patients with major depression, mainly in
the left anterior region of the brain, which has been called fron-
tal alpha asymmetry (Monakhov & Perris, 1980; Pollock &
Schneider, 1990; Alper, 1995; Debener et al., 2000; Allen &
Cohen, 2010) and has been interpreted as frontal hypoactivation
(Henriques & Davidson, 1991). Although the current study did
not find significant differences in relative theta power, the mul-
tiple regression analysis showed that both theta and alpha rela-
tive power (slow activity) were significant predictors of depres-
sive symptoms, explaining 14.57% of variance, and were nega-
tively associated with Beck depression scores. An increase in
slow (theta and alpha) activity and a diffuse enhancement of
beta power were found in patients with early stages of depres-
sion at parietal and occipital sites, reflecting decreased cortical
activation in these regions (Grin-Yatsenko, Baas, Ponomarev &
Kropotov, 2010). EEG maps of menopausal women with major
depression also demonstrated less total power, less alpha power
and more relative delta power, suggesting vigilance decrement
(Saletu et al. 1996) and an augmentation of relative delta/theta
and beta activity (Saletu, Anderer, & Saletu-Zyhlarz, 2010). A
study reported that depressed individuals exhibited higher base-
line EEG theta activity within the region of the rostral anterior
cingulated cortex, and this activity in the left precuneus was
negatively correlated with changes in Beck depression scores
(Pizzagalli et al., 2001). Clinical features of major depression
disorder have been associated with decreased dorso prefrontal
cortex and dorsal anterior cingulated gyrus activity (Brody,
Barsom, Bota, & Saxena, 2001). The beta2 frequency band has
been recorded in different conditions of increased alertness
(Steriade, 1993) and has been correlated with poorer health
status and age in depressed subjects (Morgan et al., 2005).
Furthermore, serum levels of progesterone were inversely
correlated with slow activity (the theta band involved in emo-
tional processes) and were positively correlated with fast activ-
ity (the beta2 band involved in arousal) in the group of women
with moderate depressive symptoms analyzed here. Accumu-
lating evidence indicates that progesterone induces negative
mood, most likely mediated via the action of progesterone me-
tabolites binding to the GABAA receptor complex potentiating
GABAergic inhibitory mechanisms and hence excitability (Ma-
jewska, Harrison, Schwartz, Barker, & Paul, 1986; Rupprecht,
Hauser, Trapp, & Holsboer, 1996; Eser et al., 2006; Amin et al.,
2006; Wang, 2011). Although serum progesterone levels are
low in the postmenopausal period, the concentrations of pro-
gesterone and its metabolite, allopregnanolone, are high in the
postmenopausal brain, particularly in amygdale (Bixo, Anders-
son, Winblad, Purdy, & Bäckström, 1997), brain structure in-
volved in mood. Allopregnanolone also has the ability to poten-
tiate GABAA-mediated inhibition of serotonergic neurons of
the dorsal raphe nucleus (Robichaud & Debonnel, 2006; Kaura,
Ingram, Gartside, Young, & Judge, 2007), which seems to have
relevance for depressive mood.
In contrast, in the group of women with minimal depressive
symptoms analyzed in the present study, serum levels of estra-
diol were also positively correlated with slow activity (relative
theta power), whereas levels of estradiol and estrone were in-
versely correlated with fast activity (alpha2 and beta2 bands).
Furthermore, estradiol was confirmed to as a predictor of de-
pression in the multiple correlation analysis, which was nega-
tively associated with moderate depressive symptoms. These
results suggest that serum levels of estrogens appear to influ-
ence the mechanisms that modulate emotional processes, indi-
cated by theta activity involved in emotional regulation (Nied-
ermeyer, 1993; Knyazev, 2007), favoring the manifestation of
minimal depressive symptoms. At the same time, they maintain
low arousal, indicated by the fast activity. This finding is con-
sistent with other studies that have proposed that the marked
decrease of estrogen at menopause and postmenopause could
explain depressive symptoms because a decrease in estrogen
results in decreased density of serotonin receptors and lower
activity of serotonin (Joffe & Cohen, 1998; Rybaczyk et al.,
2005; Lasiuk & Hegadoren, 2007) with hormonal effects on
neurotransmitters and mood (Soares & Zitek, 2008). Estradiol
binds with a high affinity to both estrogen receptor (ER) iso-
forms, ERα and ERβ, which are expressed in many regions of
the brain in rats including the amygdale, brain region is known
to be involved in the modulation of mood (Osterlund, Keller, &
Hurd, 2000; McEwen, 2001). Estrogen receptors and serotonin
receptors coexist in cells in a wide variety of tissues, suggesting
that many of the effects of estradiol receptors may be mediated
by changes in the actions of serotonin (Rybaczyk et al., 2005).
Therefore, it is plausible that these changes are related to mood
and brain function in females with low circulating levels of
estradiol in the postmenopausal period.
In conclusion, the current findings suggest that slow and fast
EEG relative power, estradiol and menopausal years are pre-
dictors of depressive symptoms in postmenopausal women
without a diagnosis of major depression. These findings also
add information on role of progesterone on brain function for
postmenopausal depressive symptoms and must be considered
838

S. SOLÍS-ORTIZ ET AL.
for hormone treatments.
There are some limitations that must be addressed in the
present study. This study was conducted in a specific sample of
postmenopausal women with low levels of estrogen and with-
out major depression. The study did not include postmeno-
pausal women with hormone replacement therapy and with a
diagnosis of major depression, which must be included in fu-
ture approaches. Another limitation of the study is that included
a group of women between 48 and 65 years. Other studies must
include individuals of different ages and gender. Prospective
and longitudinal designs that include hormone replacement
therapy with estrogen and progesterone in patients with depres-
sion and brain function analysis may contribute to improve
understanding of depressive symptoms on cortical activity.
Author Contributions
SSO conceived, designed, and performed the study and data
analysis and drafted the manuscript. EPL conducted the hor-
monal analyses. MPPZ performed the study and contributed to
the data analysis. All authors have read and approved the final
manuscript.
Acknowledgements
This work was supported by the University of Guanajuato.
The authors wish to acknowledge the participation of Ma. Ter-
esa Sepúlveda-Angulo in the recruitment of some participants.
Ma. del Pilar Pacheco-Zavala received a CONACYT scholar-
ship (184999) for work on her master’s degree.
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