A review of infrared thermography as applied to human sexual psychophysiology

The elusive concept of sexual motivation: can it be anchored in the nervous system?

Sexual motivation is an abstract concept referring to the mechanisms determining the responsivity to sexually relevant stimuli. This responsivity determines the likelihood of producing a sexual response and the intensity of that response. Both responsivity to stimuli and the likelihood of making a response as well as the intensity of response are characteristics of an individual. Therefore, we need to assume that the concept of sexual motivation materializes in physiological mechanisms within the individual. The aim of the present communication is to analyze the requisites for the endeavor to materialize sexual motivation. The first requisite is to provide an operational definition, making the concept quantifiable. We show that parameters of copulatory behavior are inappropriate. We argue that the intensity of sexual approach behaviors provides the best estimate of sexual motivation in non-human animals, whereas the magnitude of genital responses is an exquisite indicator of human sexual motivation. Having assured how to quantify sexual motivation, we can then proceed to the search for physiological or neurobiological underpinnings. In fact, sexual motivation only manifests itself in animals exposed to appropriate amounts of gonadal hormones. In female rats, the estrogen receptor α in the ventrolateral part of the ventromedial nucleus of the hypothalamus is necessary for the expression of sexual approach behaviors. In male rats, androgen receptors within the medial preoptic area are crucial. Thus, in rats sexual motivation can be localized to specific brain structures, and even to specific cells within these structures. In humans, it is not even known if sexual motivation is materialized in the brain or in peripheral structures. Substantial efforts have been made to determine the relationship between the activity of neurotransmitters and the intensity of sexual motivation, particularly in rodents. The results of this effort have been meager. Likewise, efforts of finding drugs to stimulate sexual motivation, particularly in women complaining of low sexual desire, have produced dismal results. In sum, it appears that the abstract concept of sexual motivation can be reliably quantified, and the neurobiological bases can be described in non-human animals. In humans, objective quantification is feasible, but the neurobiological substrate remains enigmatic.

Breath chemical markers of sexual arousal in humans

The chemical composition of exhaled breath was examined for volatile organic compound (VOC) indicators of sexual arousal in human beings. Participants (12-male, 12-female) were shown a randomized series of three emotion-inducing 10-min film clips interspersed with 3-min neutral film clips. The films caused different arousals: sports film (positive-nonsexual); horror film (negative-nonsexual); and erotic (sexual) that were monitored with physiological measurements including genital response and temperature. Simultaneously the breath was monitored for VOC and CO₂. While some breath compounds (methanol and acetone) changed uniformly irrespective of the film order, several compounds did show significant arousal associated changes. For both genders CO₂ and isoprene decreased in the sex clip. Some male individuals showed particularly strong increases of indole, phenol and cresol coincident with sexual arousal that decreased rapidly afterwards. These VOCs are degradation products of tyrosine and tryptophan, precursors for dopamine, noradrenalin, and serotonin, and therefore represent potential breath markers of sexual arousal.

Establishing a Thermal Imaging Technology (IRT) Based System for Evaluating Rat Erectile Function

Introduction

Measurement of intra-cavernous pressure (ICP) is an internationally recognized method to evaluate erectile function of animals, however, this process is invasive, destructive, and cannot be repeated, leading to a daunting challenge for monitoring the changes in erectile function throughout the whole treatment duration.

Aim

To verify whether infrared ray thermography technology based system could be a good substitution of ICP for evaluating rat erectile function.

Methods

A novel thermal image-based method, infrared ray thermography technology (IRT) was employed to monitor erectile function in erectile dysfunction (ED) rats. To detect the sensitivity and specificity of this new technology, 4 ED rat models (Diabetic, nerve-injury, vascular-injury and aged ED models) were established and subjected to both ICP and IRT test.

Outcomes

Statistical comparisons were done to test the effectiveness of this new way for detecting and dynamically monitoring erectile function.

Results

Based on the data curves obtained from ICP and IRT, the IRT showed a similar trend (including peak value, climbing speed) as that of ICP. IRT is considered as a precise way to monitor the real-time changes of erectile function in all ED rat models. The AUC of peak temperature detected by IRT in DMED, aged ED, vascular-injury ED, the nerve-injury ED and total ED rat models were 0.9811,0.9836,0.9893,0.9989 and 0.9882, respectively. Meanwhile, the AUC of temperature climbing rate were 0.6486,0.8357,0.9184,0.8675and 0.8168.Also,it is a non-invasive process of dynamically monitoring erectile function of a same rat at different time points (before and after drug intervention). The data showed that the real-time recovery by tadalafil was obtained by IRT methods even after treatment for only 2 weeks in the diabetic ED (DMED) rat model.

Conclusion

A novel noninvasive method for monitoring erectile function in rat ED models was established, and can replace or supplement ICP test.

Liu S, Zhao Z, Wang Z et al. Establishing a Thermal Imaging Technology (IRT) Based System for Evaluating Rat Erectile Function. Sex Med 2022;10:100475.

Can the Vaginal Photoplethysmograph and Its Associated Methodology Be Used to Assess Anal Vasocongestion in Women and Men?

Forty years ago, researchers documented changes in vascular and muscular activity within the anal canal of women and men who engaged in sexual self-stimulation. Vascular changes were assessed using a photoplethysmograph that aimed to detect changes in pelvic vasocongestion. An important advantage of detecting sexual response within the anal canal is that the device, its anatomical placement, and the data output are identical for women and men, therefore facilitating gender comparisons of response patterns. In this study, the vaginal photoplethysmograph (VPP), the most common measure of genital response in women, was administered intra-anally as an anal photoplethysmograph (APG) to examine its validity and sensitivity as an indicator of sexual response. The final sample comprised 20 women and 20 men who were exposed to 12, 90-s sexual and nonsexual film clips while their APG responses were recorded. Participants also rated their sexual arousal and affective responses to the stimuli. There was evidence that APG responses were specific to sexual stimuli and were sensitive to erotic intensity in women. The degree of discrimination between sexual and nonsexual stimuli was lower in men. Unlike most sexual psychophysiological studies, the positive correlation between physiological and self-reported sexual arousal was stronger in women than in men. There was a relatively high number of data artifacts and the waveform morphology was uncharacteristic of that typically observed with VPP. The potential role of anal musculature interference on the APG signal is discussed, as well as avenues for future research.

How Relevant is the Systemic Oxytocin Concentration for Human Sexual Behavior? A Systematic Review

Introduction

Despite its role in social cognition and affiliative behavior, less is known about the role played by oxytocin in human sexual behavior.

Aim

In the present systematic review, we aimed to find the levels of oxytocin related to human sexual arousal and orgasm.

Methods

We conducted the study according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. We performed a systematic search in the principal databases for studies that reported collection of salivary or plasmatic samples, with dosage of oxytocin in relation to sexual activity during induction of sexual arousal and orgasm.

Results

414 articles were obtained. After duplicates removal and the application of pre exclusion criteria, 16 articles were considered eligible and 13 articles were included with a Cohen's k of 0.827. Most of the studies used sexual self-stimulation and collected plasmatic or salivary samples to measure oxytocin. The sexual arousal and orgasm were assessed based on subjective reports.

Main Outcome Measure

The primary outcomes were the oxytocin levels collected during the induction of sexual arousal and orgasm.

Conclusions

Several studies collected only subjective reports about the sexual arousal and the orgasm. Most of the studies found higher levels of oxytocin during the orgasm or ejaculation. Given the sexual arousal evoked by self-stimulation in which sexual fantasies play an important role, it should be possible to postulate for a role of the oxytocin in sexual desire. In particular, we hypothesize a complex role of the oxytocin in the modulation of sexual fantasies and thoughts that are relevant in the sexual desire and help to trigger genital and sexual arousal.

Cera N, Vargas-Cáceres S, Oliveira C, et al. How Relevant is the Systemic Oxytocin Concentration for Human Sexual Behavior? A Systematic Review. Sex Med 2021;9:100370.