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

Neuroendocrinology of sexual behavior

One of the consequences of sexual behavior is reproduction. Thus, this behavior is essential for the survival of the species. However, the individual engaged in sexual behavior is rarely aware of its reproductive consequences. In fact, the human is probably the only species in which sexual acts may be performed with the explicit purpose of reproduction. Most human sexual activities as well as sex in other animals is performed with the aim of obtaining a state of positive affect. This makes sexual behavior important for wellbeing as well as for reproduction. It is not surprising, then, that sexual health has become an increasingly important issue, and that knowledge of the basic mechanisms controlling that behavior are urgently needed. The endocrine control of sexual behavior has been extensively studied, and although it is established that gonadal hormones are necessary, some controversy still exists concerning which hormone does what in which species. The brain areas necessary for sexual behavior have been determined in almost all vertebrates except the human. The medial preoptic area is crucial in males of all non-human vertebrates, whereas the ventromedial nucleus of the hypothalamus is important in females. Modulatory functions have been ascribed to several other brain areas.

Women and men with distressing low sexual desire exhibit sexually dimorphic brain processing

Distressing low sexual desire, termed Hypoactive Sexual Desire Disorder (HSDD), affects approximately 10% of women and 8% of men. In women, the 'top-down' theory of HSDD describes hyperactivity in higher-level cognitive brain regions, suppressing lower-level emotional/sexual brain areas. However, it is unknown how this neurofunctional disturbance compares to HSDD in men. To investigate this, we employed task-based functional MRI in 32 women and 32 men with HSDD to measure sexual-brain processing during sexual versus non-sexual videos, as well as psychometric questionnaires to assess sexual desire/arousal. We demonstrate that women had greater activation in higher-level and lower-level brain regions, compared to men. Indeed, women who had greater hypothalamic activation in response to sexual videos, reported higher psychometric scores in the evaluative (r = 0.55, P = 0.001), motivational (r = 0.56, P = 0.003), and physiological (r = 0.57, P = 0.0006) domains of sexual desire and arousal after watching the sexual videos in the scanner. By contrast, no similar correlations were observed in men. Taken together, this is the first direct comparison of the neural correlates of distressing low sexual desire between women and men. The data supports the 'top-down' theory of HSDD in women, whereas in men HSDD appears to be associated with different neurofunctional processes.

The standardization of a new Explicit Pornographic Picture Set (EPPS)

Pictures with affective content have been extensively used in scientific studies of emotion and sexuality. However, only a few standardized picture sets have been developed that offer explicit images, with most lacking pornographic pictures depicting diverse sexual practices. This study aimed to fill this gap through developing a standardized affective set of diverse pornographic pictures (masturbation, oral sex, vaginal sex, anal sex, group sex, paraphilia) of same-sex and opposite-sex content, offering dimensional affective ratings of valence, arousal, and dominance, as well as co-elicited discrete emotions (disgust, moral and ethical acceptance). In total, 192 pornographic pictures acquired from online pornography platforms and 24 control IAPS images have been rated by 319 participants (Mage = 22.66, SDage = 4.66) with self-reported same- and opposite-sex sexual attraction. Stimuli were representative of the entire affective space, including positively and negatively perceived pictures. Participants showed differential affective perception of pornographic pictures according to gender and sexual attraction. Differences in affective ratings related to participants' gender and sexual attraction, as well as stimuli content (depicted sexual practices and sexes). From the stimuli set, researchers can select explicit pornographic pictures based on the obtained affective ratings and technical parameters (i.e., pixel size, luminosity, color space, contrast, chromatic complexity, spatial frequency, entropy). The stimuli set may be considered a valid tool of diverse explicit pornographic pictures covering the affective space, in particular, for women and men with same- and opposite-sex sexual attraction. This new explicit pornographic picture set (EPPS) is available to the scientific community for non-commercial use.

Use of sexual stimuli in research and clinical settings: expert opinion and recommendations

Background

Sexual stimuli, such as sexual videos, images, and narratives describing sexual interactions, are one of many tools used by clinicians and researchers to elicit or augment sexual response. Given the wide variability within sexual stimuli and their effects on sexual response, we provide guidance on when and how to use sexual stimuli, selecting sexual stimuli, and standardizing the use and reporting of sexual stimuli in research and clinical practice.

Aim

This expert opinion review article discusses standard operating procedures when using sexual stimuli in clinical and research applications, addressing 3 broad areas: settings in which sexual stimuli are used, characteristics and contexts of the stimuli, and practical and ethical considerations when using the stimuli.

Methods

This article is based on an expert opinion review of the sexual psychophysiology literature.

Results

First, we discuss the settings in which sexual stimuli are typically used and evaluate the ecological validity of each setting. Second, we review the types of sexual stimuli used in sexual response research, including physical characteristics, depicted sexual activity, and context, and the impacts of these characteristics on sexual response. Last, we discuss the practical and ethical considerations that come with the choice and use of sexual stimuli in clinical and research settings. We address potential limitations of certain sexual stimuli, including practical and ethical considerations such as participant vs experimenter choice, diversity and representation, and proper sourcing of sexual stimuli for use in clinical and research applications. Discussions on the future applications of sexual stimuli, such as the use of virtual reality, and ethical considerations in terms of user-generated Internet sexual stimuli are also explored.

Conclusion

We provide an expert opinion review of the literature regarding use of sexual stimuli for clinical and research applications and offer best use practices and recommendations.

The Brain Activation-Based Sexual Image Classifier (BASIC): A Sensitive and Specific fMRI Activity Pattern for Sexual Image Processing

Previous studies suggest there is a complex relationship between sexual and general affective stimulus processing, which varies across individuals and situations. We examined whether sexual and general affective processing can be distinguished at the brain level. In addition, we explored to what degree possible distinctions are generalizable across individuals and different types of sexual stimuli, and whether they are limited to the engagement of lower-level processes, such as the detection of visual features. Data on sexual images, nonsexual positive and negative images, and neutral images from Wehrum et al. (2013) (N = 100) were reanalyzed using multivariate support vector machine models to create the brain activation-based sexual image classifier (BASIC) model. This model was tested for sensitivity, specificity, and generalizability in cross-validation (N = 100) and an independent test cohort (N = 18; Kragel et al. 2019). The BASIC model showed highly accurate performance (94–100%) in classifying sexual versus neutral or nonsexual affective images in both datasets with forced choice tests. Virtual lesions and tests of individual large-scale networks (e.g., visual or attention networks) show that individual networks are neither necessary nor sufficient to classify sexual versus nonsexual stimulus processing. Thus, responses to sexual images are distributed across brain systems.