Introduction

Sexual motivation involves the brain’s emotional, thinking, and movement systems working together to drive actions like approaching or initiating sexual activity. Sexual arousal and lying can affect brain activity, which can be measured through motor-evoked potentials (MEPs). MEPs are signals recorded from muscles when specific brain areas, like the motor cortex, are stimulated using transcranial magnetic stimulation (TMS), which uses electromagnetic pulses to temporarily activate parts of the brain.

Previous research showed that men’s MEPs increased when viewing sexually preferred images, such as women for heterosexual men. However, most studies have focused on men, leaving women underrepresented. Therefore, a new study aimed to see if women show similar brain responses when viewing images of men and to explore whether lying about sexual interest also changes MEPs.

The researchers expected heterosexual men to show higher MEPs for female images and heterosexual women to show higher MEPs for male images. They also examined whether lying while viewing these images increases brain activity.

Methods

For this study, 16 heterosexual monogamous couples (ages 18–35) were asked to participate in a TMS experiment to explore responses to visual stimuli. Participants were recruited through phone calls and online questionnaires, followed by in-person sessions that included informed consent, the TMS experiment, and a final questionnaire. Couples were required to have been in relationships for at least six months, and both partners needed to meet strict inclusion criteria, such as no neurological or psychiatric conditions and right-handedness.

During the experiment, participants viewed images of clothed and censored individuals of both sexes, as well as neutral scrambled images. Each trial began with an image, followed by a question: “Do you want to see the depicted person naked?” Participants had to answer truthfully in some blocks and lie in others, with responses recorded via a keyboard. TMS pulses were applied during each trial to measure motor cortex excitability, which was reflected in the muscle responses of the participants’ fingers.

The study excluded nearly 20% of trials due to technical or participant-related issues (e.g., no response), leaving over 9,000 valid trials. Data from these trials were analyzed to understand the effects of truth-telling versus lying, and the responses to male versus female images, in both men and women. Statistical methods assessed differences in brain and muscle activity based on these variables.

This rigorous methodology aimed to ensure consistency and reliability, with multiple layers of analysis, including participant-reported ease of lying and ratings of the images’ emotional and sexual impact. Ethical approval for the study was granted by the University of Regensburg, and all participants gave informed consent.

Results

The study found that both groups found it relatively easy to lie, with most participants stating they lied convincingly. Men rated images of women as more emotionally engaging and sexually arousing compared to how women rated images of men.

When asked if they wanted to see nude images of their preferred gender, nearly all participants (95% of women and 98% of men) answered “yes” in the truthful condition, but this response flipped during lying.

Tests on brain activity (measured by motor evoked potentials or MEPs) showed no major differences between genders, types of images, or whether participants were truthful or lying. However, in the truthful condition, brain activity was slightly higher for preferred sexual images than for non-preferred ones.

In lying versus truthful conditions, higher brain activity was observed overall, but the differences were small and mostly not statistically significant, except for specific neutral images in men. These findings suggest subtle sex-based differences in emotional and physiological responses to sexual and neutral stimuli, but the overall effects were minor.

Discussion & Conclusion

This is the first study showing that women’s brains react similarly to preferred sexual stimuli as men’s do. In general, men responded more strongly to female images, and women to male images, though the differences were small.

Interestingly, lying about sexual motivation increased brain activity compared to being truthful, but the differences were not strong enough to conclude that motor cortex activity could reliably measure lying or sexual preferences. The study also noted that factors like being in long-term relationships or the quality of the images (e.g., using neutral backgrounds) might have reduced participants’ sexual responses, especially for women.

Additionally, participants’ responses in this study were more uniform than in earlier research, possibly due to the study design. Long testing times or unclear instructions may have led to fatigue or less thoughtful answers. Future studies could adjust these factors to improve accuracy. Overall, while lying and sexual stimuli influence brain activity, the results suggest these measures are not yet reliable for diagnostic purposes.

References:

• Ruhland, S., Poeppl, T. B., Schoisswohl, S., Schwitzgebel, F., Osnabrügge, M., Kanig, C., Langguth, B., & Schecklmann, M. (2024). Motor-evoked potentials as biomarkers for sexual arousal? The Journal of Sexual Medicine, 21(11), 1004–1010. https://doi.org/10.1093/jsxmed/qdae122