Brain response to visual sexual stimuli in heterosexual and homosexual males

Abstract

Although heterosexual and homosexual individuals clearly show differences in subjective response to heterosexual and homosexual sexual stimuli, the neurobiological processes underlying sexual orientation are largely unknown. We addressed the question whether the expected differences in subjective response to visual heterosexual and homosexual stimuli may be reflected in differences in brain activation pattern. Twenty-four healthy male volunteers, 12 heterosexuals and 12 homosexuals, were included in the study. BOLD signal was measured while subjects were viewing erotic videos of heterosexual and homosexual content. SPM02 was used for data analysis. Individual sexual arousal was assessed by subjective rating. As compared to viewing sexually neutral videos, viewing erotic videos led to a brain activation pattern characteristic for sexual arousal in both groups only when subjects were viewing videos of their respective sexual orientation. Particularly, activation in the hypothalamus, a key brain area in sexual function, was correlated with sexual arousal. Conversely, when viewing videos opposite to their sexual orientation both groups showed absent hypothalamic activation. Moreover, the activation pattern found in both groups suggests that stimuli of opposite sexual orientation triggered intense autonomic response and may be perceived, at least to some extent, as aversive.

Figure 1

Mean sexual arousal ratings of heterosexual and homosexual subjects. Individual sexual arousal was assessed by subjective rating, using a rating scale based on the ASES, with 0 = lowest and 10 = highest. Each subject rated the heterosexual and the homosexual stimuli immediately after functional imaging. Error bars indicate standard error of the mean.

Figure 2

Regional maps of activation contrasts for sexual visual stimuli corresponding to the individual's sexual orientation (COR: A, B) and for sexual visual stimuli opposite to the individual's sexual orientation (OPP: C, D); both versus sexually neutral visual stimuli in heterosexual males (HET: A, C) and homosexual males (HOM: B, D). Statistical threshold P < 0.001 (uncorrected) for a minimum of five adjacent voxels. The right hemisphere is on the left of the coronal images and on the top of the axial images. Color bars indicate maximal Z values. (A) Bilateral occipito‐temporal, right insular and left caudate nucleus activation, absent anterior insular/inferior frontal activation in HET for the COR contrast. (B) Bilateral occipito‐temporal activation, absent anterior insular/inferior frontal activation in HOM for the COR contrast. (C) Bilateral occipito‐temporo‐parietal activation, strong bilateral anterior insular/inferior frontal activation in HET when viewing OPP. (D) Bilateral occipito‐temporal, right frontal and left caudate nucleus activation together with strong bilateral anterior insular/inferior frontal activation in HOM for the OPP contrast.

Figure 3

Coronal and sagittal view images showing activation maps of the comparison analysis (A, B, E, F) and regression analysis (C, D) of hypothalamic activation in heterosexual males (A, C, E) and homosexual males (B, D, F). The statistical threshold was set P < 0.05 (uncorrected). The right hemisphere is on the left of the coronal images. Color bars indicate maximal Z values. The activations in the ventricular system and corpus callosum seen in A, B, and C represent artifacts. (A) HET COR minus HOM OPP contrast showing strong hypothalamic activation. (B) HOM COR minus HET OPP contrast showing some hypothalamic activation. (C) HET COR contrast with subjective rating of sexual arousal as a regressor revealing strong hypothalamic activation. (D) HOM COR contrast with subjective rating of sexual arousal as a regressor again showing some hypothalamic activation. (E) HET OPP minus HOM COR contrast with absent hypothalamic activation. (F) Absent hypothalamic activation also in HOM COR minus HET OPP contrast.