Posttraumatic Stress Disorder-Related Differences in Neural Connectivity Among Female Trauma Survivors

Abstract

Background

Posttraumatic stress disorder (PTSD) is a debilitating condition that disproportionately impacts females. Prior research indicates that males with PTSD exhibit hypoconnectivity of frontal brain regions measured with resting electroencephalography (EEG). In the current study, we examined functional connectivity among females with PTSD and trauma-exposed control females, as well as the impact of sex hormones.

Methods

Participants included 61 females (mean age = 31.41 years, SD = 8.64) who endorsed criterion A trauma exposure. Resting-state EEG data were recorded for 5 minutes in the eyes-open position. Using a linear mixed-effects model, functional connectivity of the theta band (4–7 Hz) served as the response variable.

Results

Compared with the control group, the PTSD group showed hyperconnectivity between visual brain regions and the rest of the cerebral cortex (false discovery rate–corrected p [p_FDR] < .05). Additionally, participants with PTSD demonstrated enhanced connectivity between the default mode network and frontoparietal control network compared with control participants (p_FDR < .05), as well as increased connectivity between the ventral attention network and the rest of the cerebral cortex (p_FDR < .05). Estradiol was associated with higher connectivity, while progesterone was associated with lower connectivity, but these associations did not survive correction.

Conclusions

The results are consistent with prior research indicating that PTSD is associated with altered connectivity in visual brain regions, which may reflect disrupted visual processing related to reexperiencing symptoms (e.g., intrusive memories). Our findings provide additional support for the relevance of the theta frequency range in PTSD given its role in fear learning and regulation processes.

Plain Language Summary

Men with posttraumatic stress disorder (PTSD) have been shown to have lower connectivity between brain regions that are related to emotion regulation. Our goal was to examine these same brain regions in a trauma-exposed female sample. Brain activity was measured using electroencephalography (EEG) while participants rested for 5 minutes. We found that the PTSD group had higher connectivity between brain regions involved in visual processing, which is consistent with prior research. Specifically, our findings suggest that people with PTSD may have higher brain activity in regions that are involved with perceiving threat in the environment.

Plain Language Summary

Men with posttraumatic stress disorder (PTSD) have been shown to have lower connectivity between brain regions that are related to emotion regulation. Our goal was to examine these same brain regions in a trauma-exposed female sample. Brain activity was measured using electroencephalography (EEG) while participants rested for 5 minutes. We found that the PTSD group had higher connectivity between brain regions involved in visual processing, which is consistent with prior research. Specifically, our findings suggest that people with PTSD may have higher brain activity in regions that are involved with perceiving threat in the environment.

Posttraumatic stress disorder (PTSD) is a debilitating condition that involves reexperiencing symptoms, avoidance of trauma reminders, negative changes in thinking and mood, and altered arousal following a traumatic event (1). Notably, PTSD is twice as common among female trauma survivors (2). Both magnetic resonance imaging (MRI) and electroencephalography (EEG) techniques have captured important insights into altered fear processing among individuals with PTSD, and recent studies have begun to shed light on sex-specific neural alterations in this population (3). Given that sex hormones (e.g., estradiol [E2]) are known to regulate certain neural processes (4,5), additional research is needed to characterize these effects in female trauma survivors. It is worth noting that many studies use the term women to refer to individuals whose biological sex is female but who may or may not identify as women. Consistent with National Institutes of Health recommendations, we consider sex as a biological variable (e.g., female, male) and gender as a social and cultural variable (e.g., woman, nonbinary) (6).

Numerous MRI-based studies have demonstrated that PTSD is associated with hypoactivity of frontal brain regions, such as the ventromedial prefrontal cortex (vmPFC), during fear extinction (7,8) and Go/NoGo inhibition tasks (9). Additionally, resting-state MRI studies have captured reduced connectivity between the vmPFC and limbic structures involved in the fear response, such as the amygdala and hippocampus (10,11). As reviewed by Koch et al. (12), hypoactivation of the vmPFC among individuals with PTSD is thought to reflect diminished top-down regulation, or inhibition, of the fear response during nonthreatening situations. Consistent with clinical presentations of PTSD, unchecked activation of the amygdala is associated with hypervigilance and hyperarousal (13).

Several high-density EEG studies have now replicated MRI-based studies in PTSD. For example, a resting-state EEG study of civilians with PTSD demonstrated decreased functional connectivity of frontal brain regions within the beta and gamma frequency bands (14). Similarly, in their resting-state EEG study of male combat veterans with PTSD, Toll et al. (15) observed hypoconnectivity of the orbital and anterior middle frontal gyri—structures located in the frontal lobe. These findings were detected with a novel analytical technique that involves source localization and orthogonalization of amplitude correlations. Importantly, the results were significant in the theta frequency band (4–7 Hz). Theta oscillations are thought to facilitate information transfer between key regions of the fear network, including the amygdala, vmPFC, and dorsomedial prefrontal cortex, thereby enabling individuals to successfully acquire a conditioned response to threatening stimuli (16,17). Additional EEG research has linked frontal-midline theta oscillations to inhibitory control in uncertain situations (18). Taken together, aberrant theta signals may result in impaired fear learning (16), as well excessive or maladaptive responses to uncertainty, such as experiential avoidance (18), both of which constitute hallmark symptoms of PTSD.

In females, PTSD has been associated with decreased vmPFC activity (19); disrupted vmPFC-amygdala connectivity (20); and decreased connectivity between the posterior cingulate cortex and the precuneus, vmPFC, hippocampus, and amygdala (21). Among these, the precuneus and posterior cingulate cortex are key components of the default mode network, which is typically active during introspective tasks such as self-reflection (22,23). In PTSD, decreased activation of the vmPFC is associated with impaired emotion regulation, while decreased connectivity between the vmPFC and amygdala is thought to contribute to a heightened fear response (20). Additionally, reduced activity and intrinsic connectivity of default mode brain regions may impair self-referential processing and the contextualization of traumatic memories (21). Taken together, these disruptions in neurocircuitry may translate to hallmark PTSD symptoms of hyperarousal (20), intrusion, dissociation, and avoidance (24).

One possible explanation for underlying neural differences between males and females with PTSD could be the fluctuation of sex hormones across the menstrual cycle. Evidence largely suggests that E2 plays a protective role against stress. For example, an MRI comparison of premenopausal females found that higher E2 levels were associated with significantly reduced activation of the hippocampus during an induction of psychosocial stress, suggesting that high E2 levels may dampen the stress response (4). Additionally, Graham and Milad (25) observed significantly worse extinction recall in women taking estrogen-inhibiting hormonal contraceptives compared with naturally cycling women. Extending this work, Bierwirth et al. (26) compared neural activity patterns among a healthy sample of males (low E2), females using hormonal contraceptives (low E2), and naturally cycling, midcycle females (high E2). Utilizing EEG and a fear-potentiated startle paradigm, the authors reported attenuated theta oscillations in the dorsal anterior cingulate cortex (DACC), as well as reduced physiological arousal, among females with high E2 levels during fear recall.

Results of research involving progesterone (Pg) and neural activity have been mixed. For example, some evidence suggests that during the midluteal phase (when Pg levels peak), females demonstrate a stronger connection between the default mode and the salience network, the network primarily responsible for shifting one’s focus from introspective tasks to unexpected external stimuli (27). The authors proposed that heightened neural, endocrine, and physiological stress reactivity during the midluteal (elevated Pg) phase makes females more vulnerable to negative memory bias, as well as affective and stress-related disorders. In contrast, Riddle et al. (5) observed that higher concentrations of Pg may be neuroprotective. Specifically, higher Pg levels were associated with increased amplitudes of theta oscillations in the frontoparietal network, the neural network primarily responsible for cognitive control processes. Additional neuroimaging research involving trauma-exposed samples is necessary to understand the complex interaction between PTSD and sex hormones, specifically in the theta frequency band.

In the current study, we examined resting functional connectivity among trauma-exposed females with and without PTSD. Based on prior research with male samples, we hypothesized that the PTSD group would demonstrate lower functional connectivity of frontal brain regions than the control group and that this difference would emerge for the theta frequency range (4–7 Hz). Given prior research that has demonstrated that low E2 levels are associated with worse PTSD severity and greater activation of the DACC, we also hypothesized that lower E2 levels would be associated with lower functional connectivity. We did not have a priori hypotheses about Pg given limited prior research in trauma and PTSD samples.

Methods and Materials

Participants included 66 individuals assigned female at birth (mean age = 31.45 years, SD = 8.92) who endorsed DSM-5 criterion A trauma exposure. In terms of race, 4 (6.1%) participants identified as Asian or South Asian, 5 (7.6%) as Black or African American, and 53 (80.3%) as White; 4 participants (6.1%) indicated that their race was not listed or chose not to respond. Eight participants (12.3%) identified as being of Latino, Hispanic, or Spanish origin.

After they had provided informed consent, participants completed psychological measures and provided a blood sample, from which E2 and Pg were assayed. Approximately one half of the sample was naturally cycling/not on hormonal birth control (n = 37, 56.9%). Participants who were naturally cycling were asked to report the first day of their last menstrual period (n = 23 [62.2%] were in the follicular phase). Participants were then prepared for the EEG measurement. The institutional review board approved all study procedures, and participants received $100 as compensation.

Psychological Measures

A demographics questionnaire was used to assess age, race/ethnicity, gender identity, marital status, education, employment, and income. Trauma exposure was measured with the Life Events Checklist (28), which is a self-report measure of 17 types of potentially traumatic events (e.g., natural disaster, sexual assault). PTSD was assessed with the Clinician-Administered PTSD Scale for DSM-5 (CAPS-5) (29).

Blood Sample

One blood draw of 44 mL was taken at the start of the visit. Blood samples were collected in EDTA tubes, wet iced immediately, centrifuged, and stored in a −80 °C freezer. Serum was quantified for E2 (pg/mL) and Pg (ng/mL) levels using mass spectrometry. The assay for E2 has a lower limit of detection of 1 pg/mL, an intra-assay coefficient of variation (CV) < 5%, and an interassay CV < 12%. The assay for Pg has a lower limit of detection of 0.05 ng/mL, an intra-assay CV < 9.3%, and an interassay CV < 10.8%.

EEG Data Acquisition

Resting-state data were recorded for 5 minutes in the eyes-open position using a 128-channel Electrical Geodesics saline EEG system, consistent with prior resting-state EEG research, including test-retest reliability studies (15,30, 31, 32, 33, 34, 35, 36, 37). At a sampling rate of 1000 Hz, this duration yields approximately 300,000 data points per channel, capturing between 1200 and 2400 theta cycles (4–8 Hz). Participants were asked to remain still in order to minimize eye blinks and movements, and they were asked to look at a fixation cross. Landmark electrodes of the high-density geodesic montage were aligned to the standard 10-20 system. Data were collected at 1000 Hz with 0.1–100 Hz analog filtering, using Cz as a reference. Impedances were kept below 100 kΩ.

EEG Data Preprocessing

EEG data were preprocessed in MATLAB (version R2022b; MathWorks, Inc.) using custom scripts that built on the EEGLAB toolbox version 2020.0. This involved a fully automated artifact rejection pipeline that has been validated in our prior work (15) and minimizes bias from subjective manual artifact rejection. The preprocessing pipeline involved 1) resampling data to 250 Hz; 2) removal of 60 Hz AC line noise artifact; 3) removal of nonphysiological low-frequency data using a 0.01-Hz high-pass filter; 4) rejection of bad epochs by thresholding the magnitude of each epoch; 5) rejection of bad channels by thresholding spatial correlations among channels; 6) exclusion of participants with more than 25% bad channels; 7) estimation of EEG signals from bad channels from the adjacent channels through spherical spline interpolation; 8) independent component analysis to remove remaining artifacts, including scalp muscle artifact, ocular artifact, and electrocardiogram artifact; 9) re-referencing signals to the common average; and 10) filtering of signals to 4 frequency ranges: theta (4–7 Hz), alpha (8–12 Hz), beta (13–30 Hz), and low gamma (31–50 Hz). To further ensure the integrity of our processed data, all channel data were visually inspected to confirm the efficacy of the automated artifact rejection and correct any potential oversights, thereby combining the strengths of automated processes with expert review. To filter the data, we employed a Hamming windowed sinc finite impulse response filter, selecting the filter order through a heuristic approach. We implemented this filter using a toolbox developed by Widmann et al. (38) and used in the previous studies (15,39).

EEG Connectivity Processing

Following initial filtering, we conducted a detailed analysis of complex-valued time-series data from each vertex in the brain’s source space. To ensure that the signals from each brain region were effectively isolated, we used orthogonalization for each vertex’s analytical signal, thereby significantly reducing signal redundancy and interference and enhancing the specificity of our connectivity measurements. Source localization was achieved using the Brainstorm toolbox, specifically using the OpenMEEG plugin to implement a boundary element model (40,41). For the source localization technique, we utilized minimum norm estimation, which excels in providing a spatially coherent distribution of neuronal activity by integrating depth weighting and regularization (42,43). This method proved particularly advantageous for our study, handling noise effectively and facilitating detailed spatial mapping in conjunction with our comprehensive head model. Subsequently, we calculated power envelopes from these orthogonalized time series and applied a logarithmic transformation to normalize the data distribution. Connectivity between regions was then assessed by calculating Pearson’s correlation coefficients between the log-transformed power envelopes of each pair of vertices. These findings were contrasted with findings obtained from raw power envelopes derived from non-orthogonalized time series, which served as a methodological comparison to highlight the effectiveness of our orthogonalization and source localization approach.

We focused our connectivity analysis on 31 regions of interest (ROIs) within the Montreal Neurological Institute space. These regions included the left and right visual area 1, somatosensory cortex (SMC), inferior frontal junction, intraparietal sulcus (IPS), frontal eye fields, supplemental eye fields, angular gyrus (ANG), posterior middle frontal gyrus (PMFG), orbital gyrus, middle temporal gyrus (MTG), anterior MFG, insula, and supramarginal gyrus (SUP), as well as the posterior cingulate cortex, mPFC, and DACC. These regions were selected based on an independent parcellation from a previous study’s analysis (16). This approach allowed us to ground our EEG ROIs in a well-established, functional MRI–based framework for major cortical connectivity networks, while adjusting for the lower resolution of EEG data. Then, we applied Fisher’s z transformation to these correlations, a statistical method that normalizes data for better comparison and analysis.

Data Analysis

For each brain connectivity measurement, we identified the central data range using the 25th and 75th percentiles. Then, we calculated the interquartile range (IQR) and established outlier thresholds at 1.5 times the IQR above and below these percentiles (15,44). Data points outside these boundaries were marked as outliers and excluded from further analysis. Next, using a linear mixed-effects model, functional connectivity of the theta band (4–7 Hz) served as the response variable. The model included PTSD diagnosis as a categorical predictor and age, marital status, education, and income as covariates. A random intercept for each participant was also incorporated into the model; models did not include random slopes. p Values derived from this analysis were corrected using a single false discovery rate (FDR) adjustment across all ROIs using the Benjamini-Hochberg method (p_FDR, 465 comparisons < .05).

To explore the relationship between theta band power envelope connectivity and levels of E2 and Pg, we also used linear mixed-effects models. This analysis covaried for age, marital status, education level, and income. In all statistical evaluations, p values were adjusted using the Benjamini-Hochberg correction method to account for multiple comparisons. This adjustment was made across 465 comparisons, with a significance threshold set at p_FDR < .05. All data analysis, including EEG processing, was conducted using MATLAB.

Results

See Table 1 for all sample descriptives. A total of 37 (56.9%) participants met diagnostic criteria for PTSD per CAPS-5. Compared with control participants, participants with PTSD demonstrated significantly increased theta band connectivity (p_FDR < .05) between visual brain regions and other areas of the cerebral cortex (Figure 1). Specifically, there was a notable increase in connectivity from the left visual brain regions to various key areas: the right supplementary eye fields, part of the dorsal attention network; the left ANG, associated with the default mode network; the left PMFG, and left MTG, all of which are components of the frontoparietal control network; and the left SUP, involved in the ventral attention network. Similarly, enhanced theta band connectivity was observed between the right visual region and left ANG and left SUP, in the PTSD group compared with the control group.

Table 1.

Demographic Characteristics of the Sample

	Mean (SD) or n (%)
Race
Asian or South Asian	4 (6.1%)
Black	5 (7.6%)
White	53 (80.3%)
Not listed	3 (4.5%)
Prefer not to respond	1 (1.5%)
Ethnicity
Non-Hispanic/Latina	57 (87.7%)
Education
High school or GED	2 (3.1%)
College	43 (66.2%)
Graduate/professional school	20 (30.7%)
Marital Status
Single	48 (73.8%)
Married or equivalent	10 (15.4%)
Divorced	7 (10.8%)
Household Income
≤$10,000	4 (6.2%)
$10,000–$24,999	8 (12.3%)
$25,000–$49,999	19 (29.2%)
$50,000–$74,999	13 (20.0%)
≥$75,000	19 (29.2%)
Prefer not to respond	2 (3.1%)
PTSD	37 (56.9%)
Naturally Cycling	37 (56.9%)
Taking Hormonal Birth Control	28 (42.4%)
Menstrual Cycle Phasea
Follicular	23 (62.2%)
Luteal	13 (35.1%)
Gender Identity
Woman	58 (89.2%)
Nonbinary	6 (9.2%)
Gender queer	1 (1.5%)
Trauma Exposure
Natural disaster	4 (6.1%)
Fire or explosion	10 (15.2%)
Accident	25 (37.9%)
Exposure to toxic substance	12 (18.2%)
Physical assault	8 (12.1%)
Sexual assault/unwanted sexual experience	3 (4.5%)
Other	2 (3.0%)
Prefer not to respond	2 (3.0%)
Age, Years	31.45 (8.92)
Estradiol, pg/mL	94.39 (99.17)
Progesterone, ng/mL	1.35 (2.67)

PTSD was determined by clinical interview (CAPS-5), and trauma exposure was determined by self-report (LEC-5 experienced).

CAPS-5, Clinician-Administered PTSD Scale for DSM-5; GED, general educational development; LEC-5, Life Events Checklist for DSM-5; PTSD, posttraumatic stress disorder.

^aOnly available for participants who were naturally cycling; n = 1 missing.

Figure 1.

Theta band hyperconnectivity in posttraumatic stress disorder (PTSD). Thirty-one regions of interest were defined in the Montreal Neurological Institute space. We created linear mixed-effects models for the functional connectivity between 465 unique pairs of the 31 regions and diagnosis (i.e., trauma-exposed vs. PTSD) in the theta band, incorporating age, marital status, education, and income as covariates. A random intercept for each participant was also incorporated into the model. The F statistics of the models associated with each connectivity pair that survived after false discovery rate correction are shown from different views. The thickness and color of the edges represent the strength of the F value. The node colors represent the network to which the node belongs. AMFG, anterior middle frontal gyrus; ANG, angular gyrus; DACC, dorsal anterior cingulate cortex; FEF, frontal eye field; IFJ, inferior frontal junction; INS, insula; IPS, intraparietal sulcus; L, left; MPFC, medial prefrontal cortex; MTG, middle temporal gyrus; ORB, orbital gyrus; PCC, posterior cingulate cortex; PMFG, posterior middle frontal gyrus; R, right; SEF, supplementary eye field; SMC, somatosensory cortex; SUP, supramarginal gyrus; V1, visual area 1 (primary visual cortex).

In addition, we noted increased theta band connectivity in the PTSD group compared with the control group between several additional brain regions. This includes heightened connectivity from the left SUP, which is a component of the ventral attention network, to various areas: the right IPS, part of the dorsal attention network; the posterior cingulate cortex and the right ANG, both associated with the default mode network; and the right SUP, also part of the ventral attention network.

As shown in Figure 2, higher E2 levels were associated with higher theta band connectivity in multiple brain regions. The most substantial correlation was observed between the left mPFC and the left IPS. Specifically, higher E2 levels were associated with stronger connectivity between the left SMC and the left ANG (t₄₃ = 3.42, uncorrected p = .001). In all E2 analyses (including sensitivity analyses in the naturally cycling group), associations were no longer significant following FDR correction.

Figure 2.

Higher estradiol levels associated with higher theta band connectivity. A linear mixed-effects model was performed between theta band connectivity among 31 regions of interest, which resulted in 465 unique connections, and estradiol levels, accounting for age, marital status, education, and income as covariates. Only correlation values with associated p values <.05 are shown. The thickness and color of the edges represent the strength of the F value, while the node colors indicate the network to which the node belongs. AMFG, anterior middle frontal gyrus; ANG, angular gyrus; DACC, dorsal anterior cingulate cortex; FEF, frontal eye field; IFJ, inferior frontal junction; INS, insula; IPS, intraparietal sulcus; L, left; MPFC, medial prefrontal cortex; MTG, middle temporal gyrus; ORB, orbital gyrus; PCC, posterior cingulate cortex; PMFG, posterior middle frontal gyrus; R, right; SEF, supplementary eye field; SMC, somatosensory cortex; SUP, supramarginal gyrus; V1, visual area 1 (primary visual cortex).

As shown in Figure 3, lower Pg levels were associated with higher theta band connectivity in multiple brain regions. Specifically, lower Pg levels were associated with stronger connectivity between the right SUP and the right ANG (t₁₉ = −2.70, uncorrected p = .016). In all Pg analyses (including sensitivity analyses in the naturally cycling group), associations were no longer significant following FDR correction. In exploratory analyses, we examined associations between the Pg/E2 ratio and connectivity measures, and no significant observations were made.

Figure 3.

Lower progesterone levels associated with higher theta band connectivity. A linear mixed-effects model was performed between theta band connectivity among 31 regions of interest, which resulted in 465 unique connections, and progesterone levels, accounting for age, marital status, education, and income as covariates. Only correlation values with associated p values <.05 are shown. The thickness and color of the edges represent the strength of the F value, while the node color indicates the network to which the node belongs. AMFG, anterior middle frontal gyrus; ANG, angular gyrus; DACC, dorsal anterior cingulate cortex; FEF, frontal eye field; IFJ, inferior frontal junction; INS, insula; IPS, intraparietal sulcus; L, left; MPFC, medial prefrontal cortex; MTG, middle temporal gyrus; ORB, orbital gyrus; PCC, posterior cingulate cortex; PMFG, posterior middle frontal gyrus; R, right; SEF, supplementary eye field; SMC, somatosensory cortex; SUP, supramarginal gyrus; V1, visual area 1 (primary visual cortex).

Discussion

Our findings provide additional support for the relevance of the theta frequency range in PTSD given its role in fear learning and regulation processes (17,45). We observed hyperconnectivity of frontal brain regions among our female sample, which is in contrast to prior research with male veterans (15), and we replicated prior work that has demonstrated altered visual connectivity among trauma-exposed populations (46, 47, 48). Furthermore, our results are consistent with prior research indicating that PTSD is associated with altered connectivity within and between the default mode network, ventral attention network, and frontoparietal control network (49). Our results also suggest that E2 and Pg may have different associations with neural activity in trauma-exposed females, regardless of PTSD status.

Consistent with prior literature, the current findings indicated altered connectivity in visual brain regions for individuals with PTSD. One prior study of predominantly male veterans reported a relationship between greater reexperiencing symptoms and both increased visual-sensorimotor and decreased visual-frontoparietal functional connectivity (50). In our study, the right and left visual brain regions demonstrated increased connectivity with regions of the default mode network, frontoparietal control network, and ventral attention network, as well as with regions of the dorsal attention network for the left visual brain region only. These alterations may reflect the disrupted visual processing related to PTSD symptoms mentioned above, and reexperiencing in particular, which has recently been shown in acutely trauma-exposed individuals (46, 47, 48). Notably, PTSD is associated with heightened emotional arousal even at rest (i.e., without stress induction or an emotional visual stimulus), as evidenced by heightened amygdala and sympathetic nervous system activity (e.g., heart rate) (10,51, 52, 53). Because one of the proposed mechanisms for this heightened arousal in PTSD is hypervigilance (e.g., constantly scanning one’s environment for threat), it follows that PTSD is associated with increased activity of brain regions involved in visuospatial processing. Further investigation is required to determine the precise nature of this relationship among females with PTSD.

Our results indicated greater connectivity between several brain regions for females with PTSD. Specifically, we observed increased connectivity within the ventral attention (i.e., salience) network as well as between the ventral attention network and various regions of the dorsal attention network, default mode network, and frontoparietal control (i.e., central executive) network. These findings are consistent with a prior study that observed a relationship between salience network connectivity and hyperarousal symptoms in PTSD, and it has been posited that individuals with PTSD are overly primed to detect salience (e.g., threat) in their environment (24). Although hyperconnectivity between the ventral attention and frontoparietal control networks has not previously been reported in PTSD, one prior study observed hyperconnectivity between these networks within the context of a subliminal threat-processing paradigm (54). Finally, our observation of hyperconnectivity of frontal brain regions is in contrast to a study of male veterans that observed hypoconnectivity of these regions (15), which emphasizes the need for sex-based comparisons that may shed light on sex-specific neural alterations in PTSD.

These results illustrate altered connectivity across several key ROIs within the theta range, which has been implicated in fear learning and regulation (17,45). Given the high prevalence of altered fear learning and general cognitive dysfunction in PTSD (55), investigations of connectivity within the theta range may offer unique insights into the neurobiological underpinnings of this relationship. It is also important to note that alpha-band oscillations have been identified as the dominant (i.e., easiest to detect) oscillations in the human brain during resting wakefulness (56). In the current study, alterations in connectivity during resting wakefulness were tested and observed only within the theta range. This suggests that the alterations in connectivity cannot purely be accounted for by the ease with which the signal was detected, which supports the conclusion that this altered connectivity reflects true differences between the PTSD and trauma-exposed control groups.

In terms of sex hormones, higher E2 levels were associated with higher connectivity between the mPFC and the left IPS (default mode network), but these associations did not survive FDR correction. While no prior research tested this in trauma-exposed females, our finding is consistent with a study that demonstrated higher neural connectivity in females during the midluteal phase of the menstrual cycle (when E2 levels are higher) (57). Given that greater connectivity in the default mode network is associated with decreased PTSD severity, this finding is also consistent with literature suggesting a protective effect of E2 (24). In contrast, lower Pg levels were associated with higher connectivity between the right SMC and regions of both the dorsal attention and salience networks, as well as between regions of the dorsal attention and frontoparietal control networks. As with E2, these associations did not survive FDR correction. While this relationship has not previously been explored in trauma-exposed females, a prior study of healthy women found greater neural connectivity within the salience network for individuals with lower relative Pg (57). Given that the hormonal associations did not survive correction for multiple testing, replication is needed.

A strength of the current study was our use of high-density EEG, coupled with a novel analytical technique involving source localization and orthogonalization, which enabled us to examine the functional connectivity of 465 ROI pairs with enhanced spatial resolution. Second, our trauma-exposed female sample allowed us to explore potential neural deficits related to PTSD among a high-risk, underrepresented demographic. Furthermore, our study utilized the CAPS-5, which is considered the gold standard in PTSD assessment. In terms of limitations, our interpretation is complicated by the inclusion of hormonal data from non-naturally cycling participants (i.e., those taking hormonal birth control). Although biological assays provide an accurate measure of circulating gonadal hormone levels, the implications of exogenous hormone administration for the relationship between gonadal hormone levels and symptoms of psychopathology are not well understood. Similarly, while most participants were premenopausal, 13 were over 40 years of age and could have been (peri)menopausal, which might have influenced E2 and Pg levels. Despite these methodological limitations, our sensitivity analyses in naturally cycling women did not lead to different results than analyses with the entire sample.

Conclusions

This is the first study, to our knowledge, to examine associations among sex hormone levels and neural connectivity in trauma-exposed females. The observed alterations in theta-based connectivity provide additional support for the role of theta in fear learning and regulation. Furthermore, our EEG-based connectivity findings of visual cortex alterations and enhanced visual sensitization in PTSD complement and validate prior MRI findings. Consistent with prior literature, our results may also suggest that higher relative E2 levels are associated with a protective effect, marked by greater neural connectivity and decreased PTSD symptomatology. Given that this association did not remain significant following correction for multiple comparisons, these findings require replication. Future studies are needed to compare these findings in larger mixed-sex samples.