Neural Correlates of Sexual Orientation in Heterosexual, Bisexual, and Homosexual Women

Sex and Sexual Orientation Differences in Dark Triad Traits, Sexual Excitation/Inhibition, and Sociosexuality

The present study sought to investigate sex and sexual orientation differences in several traits related to sexuality and sexual behavior. Examining sexual orientation differences alongside basic sex differences to help identify correlates of sexual orientation diversity, and whether individuals with varying degrees of same-sex attraction show concurrent sex-atypical shifts in other domains. Males tend to score higher than females in the Dark Triad (DT) traits of sub-clinical narcissism, psychopathy, and Machiavellianism. Similarly, females tend to be more cautious than males in their attitudes and desires toward casual sex activity (i.e., sociosexuality). These sex differences may be related to the propensity for individuals to become easily sexually excited, which is higher in males, or to instead inhibit sexual arousal, which is higher in females. In a large undergraduate sample (N = 2047), we replicated expected sex differences in DT traits, sociosexuality, and sexual excitation/inhibition. We found that non-heterosexual females were "male-shifted" in some of these traits, but these shifts tended to be strongest among mostly heterosexual and bisexual individuals. Furthermore, we found that within-sex variation in sociosexuality, sexual excitation, and sexual inhibition was not related to sexual orientation in a linear fashion. Instead, sociosexuality and sexual excitation were related to sexual orientation in a curvilinear (inverted-U) fashion, especially among females. The fact that traits correlated with bisexuality and homosexuality were somewhat distinct is consistent with the idea that different developmental pathways may lead to these discrete sexual attraction patterns.

Intersexual and Intrasexual Differences in Mate Selection Preferences Among Lesbian Women, Gay Men, and Bisexual Women and Men

Sex differences in mating strategies and partner preferences are well established. However, most research solely focused on heterosexual women and men. We examined the mate selection, marriage, and age preferences of a sample of lesbian women, gay men, and bisexual women and men (LGB) who took part in an online dating survey. Additionally, we analyzed inter- and intrasexual differences in these preferences. A total of 710 participants rated the importance of 82 mate selection criteria and 10 marriage criteria, and they also indicated their age preferences and short-term and long-term relationship orientation. An exploratory factor analysis suggested 11 relevant domains of mate selection in the LGB sample, with sex, age, and long-term relationship orientation being relevant predictors of differences in these domains. We compared the LGB data with data collected from 21,245 heterosexual women and men on the same mate selection criteria. Results showed that the participants' sex was the most important predictor of differences in mate selection and marriage preferences, while intrasexual variables (sexual orientation and relationship orientation) explained only a small part of the variance. We incorporated the results into the current discussion about partner preferences and sexual orientation.

Carving the Biodevelopment of Same-Sex Sexual Orientation at Its Joints

Sexual orientation is a core aspect of human experience and understanding its development is fundamental to psychology as a scientific discipline. Biological perspectives have played an important role in uncovering the processes that contribute to sexual orientation development. Research in this field has relied on a variety of populations, including community, clinical, and cross-cultural samples, and has commonly focused on female gynephilia (i.e., female sexual attraction to adult females) and male androphilia (i.e., male sexual attraction to adult males). Genetic, hormonal, and immunological processes all appear to influence sexual orientation. Consistent with biological perspectives, there are sexual orientation differences in brain development and evidence indicates that similar biological influences apply across cultures. An outstanding question in the field is whether the hypothesized biological influences are all part of the same process or represent different developmental pathways leading to same-sex sexual orientation. Some studies indicate that same-sex sexually oriented people can be divided into subgroups who likely experienced different biological influences. Consideration of gender expression in addition to sexual orientation might help delineate such subgroups. Thus, future research on the possible existence of such subgroups could prove to be valuable for uncovering the biological development of sexual orientation. Recommendations for such future research are discussed.

Accurate machine learning prediction of sexual orientation based on brain morphology and intrinsic functional connectivity

BACKGROUND

Sexual orientation in humans represents a multilevel construct that is grounded in both neurobiological and environmental factors.

OBJECTIVE

Here, we bring to bear a machine learning approach to predict sexual orientation from gray matter volumes (GMVs) or resting-state functional connectivity (RSFC) in a cohort of 45 heterosexual and 41 homosexual participants.

METHODS

In both brain assessments, we used penalized logistic regression models and nonparametric permutation.

RESULTS

We found an average accuracy of 62% (±6.72) for predicting sexual orientation based on GMV and an average predictive accuracy of 92% (±9.89) using RSFC. Regions in the precentral gyrus, precuneus and the prefrontal cortex were significantly informative for distinguishing heterosexual from homosexual participants in both the GMV and RSFC settings.

CONCLUSIONS

These results indicate that, aside from self-reports, RSFC offers neurobiological information valuable for highly accurate prediction of sexual orientation. We demonstrate for the first time that sexual orientation is reflected in specific patterns of RSFC, which enable personalized, brain-based predictions of this highly complex human trait. While these results are preliminary, our neurobiologically based prediction framework illustrates the great value and potential of RSFC for revealing biologically meaningful and generalizable predictive patterns in the human brain.

Sexual Complexity: A Comparison between Men and Women in a Sexual Minority Sample of Members of the Church of Jesus Christ of Latter-day Saints

We report here some of the results from an online survey of 1612 LGBTQ members and former members of the Church of Jesus Christ of Latter-day Saints (CJCLDS, Mormon). The data permitted an exploration of diversity—individual similarities and differences within and between the sexes. Men and women were compared with respect to sexual identity self-labeling and behavior (i.e., identity development, disclosure, activity), orientation change efforts, marital relationships, and psychosocial health—these variables in the context of their religious lives. More women than men self-identified in the bisexual range of the sexual attraction continuum. Both men and women had engaged in extensive effort to change their sexual orientation. Only about 4% of the respondents claimed that those efforts had been successful, and the claims were for outcomes other than an alteration in erotic feeling. In general, only those who identified as bisexual reported success in maintaining a mixed-orientation marriage and continuing activity in the church. For both men and women, measures of psychosocial and sexual health were higher for those in same-sex relationships and those disaffiliated from the church.

Structural, Functional, and Metabolic Brain Differences as a Function of Gender Identity or Sexual Orientation: A Systematic Review of the Human Neuroimaging Literature

This review systematically explored structural, functional, and metabolic features of the cisgender brain compared with the transgender brain before hormonal treatment and the heterosexual brain compared to the homosexual brain from the analysis of the neuroimaging literature up to 2018, and identified and discussed subsequent studies published up to March 2021. Our main aim was to help identifying neuroradiological brain features that have been related to human sexuality to contribute to the understanding of the biological elements involved in gender identity and sexual orientation. We analyzed 39 studies on gender identity and 24 on sexual orientation. Our results suggest that some neuroanatomical, neurophysiological, and neurometabolic features in transgender individuals resemble those of their experienced gender despite the majority resembling those from their natal sex. In homosexual individuals the majority resemble those of their same-sex heterosexual population rather than their opposite-sex heterosexual population. However, it is always difficult to interpret findings with noninvasive neuroimaging. Given the gross nature of these measures, it is possible that more differences too subtle to measure with available tools yet contributing to gender identity and sexual orientation could be found. Conflicting results contributed to the difficulty of identifying specific brain features which consistently differ between cisgender and transgender or between heterosexual and homosexual groups. The small number of studies, the small-to-moderate sample size of each study, and the heterogeneity of the investigations made it impossible to meta-analyze all the data extracted. Further studies are necessary to increase the understanding of the neurological substrates of human sexuality.

Specific factors and methodological decisions influencing brain responses to sexual stimuli in women

Most of the neuroimaging studies on sexual behavior have been conducted with male participants, leading to men-based models of sexual arousal. Here, possible factors and methodological decisions that might influence brain responses to sexual stimuli, specifically for the inclusion of women, will be reviewed. Based on this review, we suggest that future studies consider the following factors: menstrual phase, hormonal contraception use, history of sexual or psychiatric disorders or diseases, and medication use. Moreover, when researching sexual arousal, we suggest future studies assess sexual orientation and preferences, that women should select visual sexual stimuli, and a longer duration than commonly used. This review is thought to represent a useful guideline for future research in sexual arousal, which hopefully will lead to a higher inclusion of women and therefore more accurate neurobiological models of sexual arousal.

Sexual excitation and sex-linked substance use predict overall cannabis use in mostly heterosexual and bisexual women

Background: Bisexual and mostly heterosexual women report higher substance use than exclusively heterosexual or lesbian women. In sexual minority men, sex-linked substance use (SLSU) can increase risk for substance use problems; equivalent research in women is lacking.Objectives: To test if sexual excitation and inhibition mediate the association between sexual minority status and women's SLSU.Methods: We surveyed a convenience sample of 595 undergraduate women who identified as exclusively heterosexual (n = 499), mostly heterosexual (n = 59), or bisexual (n = 37). Participants reported on their last month use of alcohol, cannabis, and other drugs (e.g., cocaine) in sexual and non-sexual contexts, and symptoms of alcohol and non-alcohol drug use disorders (e.g., withdrawal symptoms). Drug use symptoms were collapsed across non-alcohol substances. We used structural equation modeling to test serial mediations of women's SLSU and overall drug and alcohol use.Results: Bisexual and mostly heterosexual women reported higher cannabis use (η2 = 0.030) and drug use disorder symptoms (η2 = 0.050) than heterosexual women. Mostly heterosexual women's SLSU was a stronger predictor of alcohol use (η2 = 0.019) and binge drinking frequency (η2 = 0.015) than for other orientation groups. Bisexual and mostly heterosexual women's higher sexual excitation predicted their higher SLSU, which in turn predicted higher cannabis use frequency and drug use disorder symptoms. However, sexual inhibition failed to mediate either SLSU or overall substance use.Conclusion: These findings point to SLSU as a mechanism by which sexual minority women may experience disparities in substance use related harms.

Understanding heterosexual women's erotic flexibility: the role of attention in sexual evaluations and neural responses to sexual stimuli

Many women experience desires, arousal and behavior that run counter to their sexual orientation (orientation inconsistent, 'OI'). Are such OI sexual experiences cognitively and neurobiologically distinct from those that are consistent with one's sexual orientation (orientation consistent, 'OC')? To address this question, we employed a mindful attention intervention-aimed at reducing judgment and enhancing somatosensory attention-to examine the underlying attentional and neurobiological processes of OC and OI sexual stimuli among predominantly heterosexual women. Women exhibited greater neural activity in response to OC, compared to OI, sexual stimuli in regions associated with implicit visual processing, volitional appraisal and attention. In contrast, women exhibited greater neural activity to OI, relative to OC, sexual stimuli in regions associated with complex visual processing and attentional shifting. Mindfully attending to OC sexual stimuli reduced distraction, amplified women's evaluations of OC stimuli as sexually arousing and deactivated the superior cerebellum. In contrast, mindfully attending to OI sexual stimuli amplified distraction, decreased women's evaluations of OI stimuli as sexually arousing and augmented parietal and temporo-occipital activity. Results of the current study constrain hypotheses of female erotic flexibility, suggesting that sexual orientation may be maintained by differences in attentional processing that cannot be voluntarily altered.

Brain structure changes associated with sexual orientation

Biological sex differences in brain function and structure are reliably associated with several cortico-subcortical brain regions. While sexual orientation (hetero- versus homosexuality) has been similarly linked to functional differences in several phylogenetically-old brain areas, the research on morphological brain phenotypes associated with sexual orientation is far from conclusive. We examined potential cerebral structural differences linked to sexual orientation in a group of 74 participants, including 37 men (21 homosexual) and 37 women (19 homosexual) using voxel-based morphometry (VBM). Gray matter volumes (GMV) were compared with respect to sexual orientation and biological sex across the entire sample using full factorial designs controlling for total intracranial volume, age, handedness, and education. We observed a significant effect of sexual orientation for the thalamus and precentral gyrus, with more GMV in heterosexual versus homosexual individuals, and for the putamen, with more GMV in homosexual + than heterosexual individuals. We found significant interactions between biological sex and sexual orientation, indicating that the significant effect for the putamen cluster was driven by homosexual women, whereas heterosexual women had increased precentral gyrus GMV. Heterosexual men exhibited more GMV in the thalamus than homosexual men. This study shows that sexual orientation is reflected in brain structure characteristics and that these differ between the sexes. The results emphasize the need to include or control for potential effects of participants' sexual orientation in neuroimaging studies. Furthermore, our findings provide important new insights into the brain morphology underlying sexual orientation and likely have important implications for understanding brain functions and behavior.

Neural and Hormonal Correlates of Sexual Arousal in Transgender Persons

BACKGROUND

Whereas mounting work has begun to document the neural correlates underlying sexual arousal (SA) in humans, the associations between gender identity and the brain correlates of SA as well as their hormonal contributions remain unknown.

AIM

This study investigated neural activation to sexual arousal in transgender and cisgender persons.

METHODS

20 transgender men and 19 transgender women (TW) already living in their identified gender were compared to 21 cisgender men (CM) and 19 cisgender women. Participants viewed erotic and neutral video clips while undergoing 3 Tesla magnetic resonance imaging.

OUTCOMES

Group-specific brain activation, brain functional connectivity, and brain-hormone associations within the neurophenomenological model of sexual arousal (Stoleru et al, 2012).

RESULTS

Consistent with the model, participants activated most of its components. However, between-group differences were mostly showing larger activation for CM relative to any of the other 3 groups. Moreover, functional connectivity analyses (psychophysiological interactions) indicated unique patterns for CM, cisgender women, and TW in how different components of SA communicated with one another. Finally, androgens in transgender men and estrogens in TW correlated negatively with parietal cortex and primary (sensori-) motor regions, respectively, while CM showed positive correlations of androgens with parietal cortex, somatosensory regions, and the insula.

CLINICAL IMPLICATIONS

Data provide information on neurobiological changes in sexual arousal during treatment with gender-affirming hormone therapy.

STRENGTHS & LIMITATIONS

Although a limitation is the lack of pretreatment data, the present study provides comprehensive information including brain activation, functional connectivity, and hormonal associations in a large sample.

CONCLUSIONS

The results highlight a complex picture of the neural correlates of SA in gender identity and sex assigned at birth. Mueller SC, Wierckx K, T'Sjoen G. Neural and Hormonal Correlates of Sexual Arousal in Transgender Persons. J Sex Med 2020;17:2495-2507.

Neural Correlates of Gender Face Perception in Transgender People

To date, MRI studies focused on brain sexual dimorphism have not explored the presence of specific neural patterns in gender dysphoria (GD) using gender discrimination tasks. Considering the central role of body image in GD, the present study aims to evaluate brain activation patterns with 3T-scanner functional MRI (fMRI) during gender face discrimination task in a sample of 20 hormone-naïve transgender and 20 cisgender individuals. Additionally, participants were asked to complete psychometric measures. The between-group analysis of average blood oxygenation level dependent (BOLD) activations of female vs. male face contrast showed a significant positive cluster in the bilateral precuneus in transmen when compared to the ciswomen. In addition. the transwomen group compared to the cismen showed higher activations also in the precuneus, as well as in the posterior cingulate gyrus, the angular gyrus and the lateral occipital cortices. Moreover, the activation of precuneus, angular gyrus, lateral occipital cortices and posterior cingulate gyrus was significantly associated with higher levels of body uneasiness. These results show for the first time the existence of a possible specific GD-neural pattern. However, it remains unclear if the differences in brain phenotype of transgender people may be the result of a sex-atypical neural development or of a lifelong experience of gender non-conformity.

Conceptualization, History, and Future of the Paraphilias

There is no accepted definition of the term paraphilia despite its being listed as an essential feature of a class of mental disorders known as the paraphilic disorders. The origin of the term, history of its inclusion as a diagnosis, and logical flaws inherent in the various definitions are discussed in this review. We examine the basis for pathologizing individuals with paraphilias, consider what paraphilias can tell us about how humans develop their sexual interests, and question the usefulness of dividing sexual interests into paraphilias and normophilias. The construct of the paraphilias appears to be poorly conceived and has outlived its usefulness.

Different Neural Correlates of Sexually Preferred and Sexually Nonpreferred Stimuli

BACKGROUND

The differences and relationships between stimulus-related brain activation for sexually preferred stimuli and sexually nonpreferred stimuli are still unclear.

AIM

This study aimed to identify brain regions that were mostly associated with sexual stimuli.

METHODS

We used the activation likelihood estimation, meta-analytic connectivity modelling, and behavioral domain metadata in the BrainMap database to perform this analysis.

OUTCOMES

We found convergent activation foci and created a model for the extended brain network involved in responses to sexual stimuli and also assessed the functional properties of these regions.

RESULTS

A total of 34 experiments from 15 studies including 368 subjects and 343 foci were analyzed. The results showed that sexual stimuli are related to the extensive activation of the occipital-temporal-limbic system and less extensive activation of the basal ganglia. Sexually preferred stimuli activated mainly the anterior cingulate cortex and right fusiform gyrus, while sexually nonpreferred stimuli activated the limbic system, occipital gyrus, and thalamus.

CLINICAL IMPLICATIONS

To have a further understanding of the central mechanisms of human sexuality.

STRENGTHS & LIMITATIONS

Patient characteristics and analysis techniques in the included studies were heterogeneous.

CONCLUSIONS

These findings suggest that the anterior cingulate cortex is an important cognitive control area for both sexually preferred and nonpreferred stimuli. Meta-analytic connectivity modelling analysis revealed a network of the core brain areas involved in response to sexual stimuli, and behavioral domain analysis indicated that these areas have both common and discrete functional properties. Long X, Tian F, Zhou Y, et al. Different Neural Correlates of Sexually Preferred and Sexually Nonpreferred Stimuli. J Sex Med 2020;17:1254-1267.

Do Bisexuals Have a Bisexual Viewing Pattern?

Past visual attention research appears to show that bisexual men and women view erotic images differently compared to heterosexual and gay/lesbian men and women. However, none of these studies have employed analytic approaches required to determine whether these apparent bisexual viewing patterns are due to averaging together heterosexual and gay/lesbian type viewing patterns, or rather are because bisexual-identified individuals possess unique viewing patterns which are distinct from heterosexual and gay/lesbian individuals. In the current eye-tracking study, we aimed to address this question. Visual attention of 60 men (24 heterosexual, 19 gay, 17 bisexual) and 54 women (21 heterosexual, 10 lesbian, 23 bisexual) was tracked, while they viewed erotic images of nude men and women. Applying analytic approaches capable of detecting bisexual responding revealed that bisexual men, but not bisexual women, had a unique bisexual controlled attention pattern, and that neither bisexual men nor women demonstrated a unique bisexual pattern of initial attention. Our findings provide mixed evidence for a unique bisexual attentional profile in men and women.

Neural Responses to Sexual Stimuli in Heterosexual and Homosexual Men and Women: Men's Responses Are More Specific

Patterns of genital arousal in response to gendered sexual stimuli (i.e., sexual stimuli presenting members of only one sex at a time) are more predictive of men's than of women's sexual orientations. Additional lines of evidence may shed light on the nature of these differences. We measured neural activation in homosexual and heterosexual men and women using fMRI while they viewed three kinds of gendered sexual stimuli: pictures of nude individuals, pictures of same-sex couples interacting, and videos of individuals self-stimulating. The primary neural region of interest was the ventral striatum (VS), an area of central importance for reward processing. For all three kinds of stimuli and for both VS activation and self-report, men's responses were more closely related to their sexual orientations compared with women's. Furthermore, men showed a much greater tendency to respond more positively to stimuli featuring one sex than to stimuli featuring the other sex, leading to higher correlations among men's responses as well as higher correlations between men's responses and their sexual orientations. Whole-brain analyses identified several other regions showing a similar pattern to the VS, and none showed an opposite pattern. Because fMRI is measured identically in men and women, our results provide the most direct evidence to date that men's sexual arousal patterns are more gender specific than women's.

Neuroanatomy and function of human sexual behavior: A neglected or unknown issue?

INTRODUCTION

Sexual desire, arousal, and orgasm are mediated by complex, yet still not fully understood, interactions of the somatic and autonomic nervous systems operating at the central and peripheral levels. Disruption of endocrine, neural, or vascular response, caused by aging, medical illness, neurological diseases, surgery, or drugs, can lead to sexual dysfunctions, thus significantly affecting patients' quality of life.

PURPOSE

This narrative review aims at characterizing the involvement of the central nervous system in human sexual behavior.

METHODS

A literature search was conducted using PubMed in its entirety up to June 2018, analyzing the studies dealing with the neurobiological and neurophysiological basis of human sexuality.

RESULTS

Sexual behavior is regulated by both subcortical structures, such as the hypothalamus, brainstem, and spinal cord, and several cortical brain areas acting as an orchestra to finely adjust this primitive, complex, and versatile behavior. At the central level, dopaminergic and serotonergic systems appear to play a significant role in various factors of sexual response, although adrenergic, cholinergic, and other neuropeptide transmitter systems may contribute as well.

CONCLUSIONS

Providing healthcare professionals with information concerning sexual behavior may overcome useless and sometimes dangerous barriers and improve patient management, since sexual well-being is considered one of the most important aspects of one's quality of life.

A Life History Approach to the Female Sexual Orientation Spectrum: Evolution, Development, Causal Mechanisms, and Health

Women's capacity for sexual fluidity is at least as interesting a phenomenon from the point of view of evolutionary biology and behavioral endocrinology as exclusively homosexual orientation. Evolutionary hypotheses for female nonheterosexuality have failed to fully account for the existence of these different categories of nonheterosexual women, while also overlooking broader data on the causal mechanisms, physiology, ontogeny, and phylogeny of female nonheterosexuality. We review the evolutionary-developmental origins of various phenotypes in the female sexual orientation spectrum using the synergistic approach of Tinbergen's four questions. We also present femme-specific and butch-specific hypotheses at proximate and ultimate levels of analysis. This review article indicates that various nonheterosexual female phenotypes emerge from and contribute to hormonally mediated fast life history strategies. Life history theory provides a biobehavioral explanatory framework for nonheterosexual women's masculinized body morphology, psychological dispositions, and their elevated likelihood of experiencing violence, substance use, obesity, teenage pregnancy, and lower general health. This pattern of life outcomes can create a feedback loop of environmental unpredictability and harshness which destabilizes intrauterine hormonal conditions in mothers, leading to a greater likelihood of fast life history strategies, global health problems, and nonheterosexual preferences in female offspring. We further explore the potential of female nonheterosexuality to function as an alloparental buffer that enables masculinizing alleles to execute their characteristic fast life history strategies as they appear in the female and the male phenotype. Synthesizing life history theory with the female sexual orientation spectrum enriches existing scientific knowledge on the evolutionary-developmental mechanisms of human sex differences.

Sexual Arousal Patterns of Identical Twins with Discordant Sexual Orientations

Genetically identical twins can differ in their self-reported sexual orientations. However, whether the twins' subjective reports reflect valid differences in their sexual orientations is unknown. Measures of sexual orientation, which are free of the limitations of self-report, include genital arousal and pupil dilation while viewing sexual stimuli depicting men or women. We examined these responses in 6 male twin pairs and 9 female twin pairs who reported discordant sexual orientations. Across measures, heterosexual male twins responded more strongly to women than to men. Their homosexual co-twins showed an opposite pattern. Heterosexual female twins responded equally to both sexes, whereas their homosexual co-twins responded somewhat more to women than men. These differences within pairs were similar to differences between unrelated heterosexual and homosexual males and females. Our study provides physiological evidence confirming twins' discordant sexual orientations, thereby supporting the importance of the non-shared environment for the development of sexual orientation and sexual arousal.