Study reveals differences in men's and women's brain responses to low sexual desire

In a recent study published in Scientific Reports, researchers examined the neurofunctional determinants of hypoactive sexual desire disorder (HDSS) in men and women. In simple terms, it is a condition in which people experience decreased sexual desire, causing anxiety. This syndrome has previously been studied in women, but never before in men. In this study, researchers used functional magnetic resonance imaging (fMRI) in combination with psychometric questionnaires to assess the neurofunctional responses of men and women to sexual and nonsexual video presentations.

This study found that women with hypoactive sexual desire follow a top-down theory, which states that hyperactivity in higher cognitive areas of the brain suppresses lower levels of sexual areas of the brain. Unlike women, men did not show this neurofunctional pattern, highlighting the sexual dimorphism in how male and female brains process sexual stimuli. Although researchers were unable to clarify the cognitive mechanisms underlying HDSS in men, this study highlights the need for more research on HDSS in men and suggests that low sexual desire treatments used for women may not produce desired results in men.

What is HDSS and what do we know about the condition?

The Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Revised (DSM-IV-TR) defines hypoactive sexual desire disorder (HDSS) as “persistent sexual fantasies and desires for sexual activity that cause marked anxiety or interpersonal difficulties.” This syndrome is popularly called “reduced sexual desire,” “hyposexuality,” or “suppressed sexual desire.” HDSS is a sexual dysfunction whose symptoms include a significant lack of sexual fantasy and arousal, even in sexually active men and women. Given the significant social and interpersonal distress caused by HDSS, the condition is often associated with depression and similar emotional disorders.

Women with HSDD show greater activation of the limbic system to sexual videos than men.

(A) Mean results of a group of women with HSDD, showing brain activation (red/yellow) and deactivation (blue/green) to sex videos compared to controls (exercise).
(B) Average results of a group of men with HSDD, showing brain activation and deactivation to sex videos compared to controls (exercise).
(C) Brain regions that are more activated in women (versus men) to sex videos compared to controls are shown in purple. Areas of the brain that are more activated in men (vs. Women) to sex videos compared to controls are shown in green.

The results are adjusted by cluster and the threshold values are Z = 2.3, P < 0.05, N = 64 (32 women, 32 men).

Study: Women with HSDD show greater activation of the limbic system to sex videos than men. (A) Mean performance of the group of women with HSDD, showing brain activation (red/yellow) and deactivation (blue/green) to sex videos compared to controls (exercise). (B) Mean performance of a group of men with HSDD, showing brain activation and deactivation to sex videos compared to controls (exercise). (C) Brain regions that are more activated in women (versus men) to sex videos compared to controls are shown in purple. Areas of the brain that are more activated in men (versus women) to sex videos compared to controls are shown in green. The results are adjusted by cluster and the threshold values are Z = 2.3, P < 0.05, N = 64 (32 women, 32 men). Study: Women and men with anxious low sexual desire show a sex difference in brain processing.

First identified in 1980 (DSM-III) and formally defined in 1987 (DSM-III-R), HDSS is a clinically distinct disorder from conditions such as asexuality and erectile dysfunction. Its causes may include a history of sexual abuse, altered sex hormone levels, or other medical conditions such as cancer, diabetes, and multiple sclerosis. Despite its relatively recent description, HDSS is one of the most common sexual disorders in the world, estimated to affect 10% of all women and 8% of all men. Given the social stigma associated with this condition, these figures are considered to be a gross underestimation, highlighting the need for interventions against the impact of neurofunctional diseases on quality of life.

Unfortunately, despite the limited research on HDSS, the available scientific literature on this topic is almost exclusively focused on women, with the only previous study in men using questionable methodologies. This difference in studies is reflected in treatment options, with two medically licensed interventions for American women and none for American men. A significant number of cases of HDSS in men are misdiagnosed as erectile dysfunction, exacerbating the stress and mental health associated with the condition.

In this study, researchers sought to use functional magnetic resonance imaging (fMRI) in combination with several psychometric questionnaires to assess the neurofunctional responses of men and women with HDSS to sexual and nonsexual stimuli (in this case, video presentations—visual sexual stimuli). The study involved men and women with clinically confirmed HDSS (ICD-11), recruited through advertisements throughout London (print and online media). Screening of participants consisted of a telephone interview followed by an in-person medical assessment (blood and questionnaires) to distinguish between acquired and generalized HDSS. To avoid confounding with existing clinical conditions, people with a history of psychiatric illness or current treatment were excluded from the study.

"...participants must have been in a stable, communicative, monogamous relationship for more than 6 months. Participants were excluded if they had a history of unresolved sexual trauma, violence or aggression, use of medications (prescription or over-the-counter), or herbal medications to enhance sexual desire, arousal or performance, or if they had contraindications to MRI scanning."

The experimental intervention involved the presentation of 20-second silent sexual videos (cases) interspersed with neutral, non-sexual exercise videos (control) for a 12-minute standardized block (rated on a Likert scale). Participants were required to complete the Sexual Desire and Arousal Inventory (SADI) immediately before and after the experimental intervention, which measured 54 descriptors in the categories of evaluative, negative, physiological, and motivational. During the experimental intervention, participants underwent simultaneous fMRI and pulse oximetry testing.

Data processing included correlations between questionnaire results and fMRI arousal images, matches between activation patterns in men and women (via Dice coefficients) for sexual and non-sexual visual stimuli, and analysis of brain regions of interest (ROIs), especially those corresponding to neural reproductive network (amygdala, hypothalamus, insular cortex, precentral gyrus, striatum and thalamus).

After the screening process, the study sample remained 32 men and 32 women with clinically confirmed HDSS. While men were on average nine years older than their female counterparts, the Dice coefficient results suggest that age did not influence the study's results. An additional 20 healthy men and women were recruited to confirm differences between sexual and nonsexual stimuli and establish baseline levels of neural activation responses.

"The results are somewhat consistent with previous studies in people with normal sexual desire, suggesting that women and men show similar overall patterns of activation to visual sexual stimuli. However, notable differences were observed in the activation of limbic brain regions in women and men with HDSS, especially the hypothalamus, amygdala and thalamus, which are key structures associated with emotional processing and sexual motivation."

The present study highlights that the neural sexual network in women with HDSS shows activation when sexual stimuli are presented; however, these “low-level” neurofunctional centers (limbic areas) are masked by the simultaneous activation of higher cortical areas, supporting the top-down hypothesis proposed by Cacioppo. In contrast, males with HDSS did not show activation of the neural sexual network, suggesting that visual sexual signals are not efficiently transmitted to emotional centers associated with sexual response. This study is the first scientific paper to explain the sexual dimorphy between male and female neurofunctional HDSS. It highlights the need for more research, particularly in men, before effective therapeutic interventions against this condition can be developed.