Asexual versus sexual women: a test-retest study on differences in brain activity

Asexuality has a prevalence of approximately 1% in the population and should not be confused with hypoactive sexual desire disorder as defined in the DSM-5. Asexuality is characterized by minimal to no sexual attraction to others. The neural correlates of asexuality remain largely unknown, and the test-retest reliability of sexually induced brain activity is still elusive. In this functional MRI study, we used the Asexual Identification Scale to identify 14 asexual women (mean score ~ 46) and 21 sexual women (mean score ~ 14). We modeled brain activity in response to sexual stimuli using the canonical hemodynamic response function and performed voxel-wise test-retest reliability analysis on contrast weight maps. Additionally, we applied pattern recognition methods to distinguish asexual from sexual women. The voxel-wise test-retest reliability of brain activity in response to sexual stimuli was remarkably robust for sexuality relevant brain areas [mean ICC(2,1) = 0.66]. The conjunction analysis comparing sexual stimuli to baseline showed that group brain activity was reproducible at a Bonferroni-corrected P value of 1.78e -6 . The direct contrast between asexual and sexual women yielded no significant differences at the single-voxel level. A support vector machine, however, identified 71% ( P  < 0.03) of asexual and sexual women correctly when test and retest runs were combined. In conclusion, although our sample size is small, our findings suggest that differences between asexual and sexual women may have their neural roots in subtle variations in brain activity across extensive brain regions, which might be identified using classification methods.