Brain response to putative pheromones in lesbian women

Abstract

The progesterone derivative 4,16-androstadien-3-one (AND) and the estrogen-like steroid estra-1,3,5(10),16-tetraen-3-ol (EST) are candidate compounds for human pheromones. In previous positron emission tomography studies, we found that smelling AND and EST activated regions primarily incorporating the sexually dimorphic nuclei of the anterior hypothalamus, that this activation was differentiated with respect to sex and compound, and that homosexual men processed AND congruently with heterosexual women rather than heterosexual men. These observations indicate involvement of the anterior hypothalamus in physiological processes related to sexual orientation in humans. We expand the information on this issue in the present study by performing identical positron emission tomography experiments on 12 lesbian women. In contrast to heterosexual women, lesbian women processed AND stimuli by the olfactory networks and not the anterior hypothalamus. Furthermore, when smelling EST, they partly shared activation of the anterior hypothalamus with heterosexual men. These data support our previous results about differentiated processing of pheromone-like stimuli in humans and further strengthen the notion of a coupling between hypothalamic neuronal circuits and sexual preferences.

Fig. 1.

Illustration of group-specific activations with the putative pheromones. The Sokoloff color scale illustrates Z values reflecting the degree of activation (0.0–5.0). Because the same brain section is chosen, the figures do not always illustrate maximal activation for each condition. (Upper) Cerebral activation during smelling of AND and EST. Clusters of activated regions are superimposed on the standard MRI brain (midsagittal plane). (Lower) Significant differences among the different groups. Shown are the clusters calculated with two-group random-effect analysis. Only significant activations are shown.

Fig. 2.

Common activations between the groups. Shown are conjunctional clusters in different groups of subjects, superimposed on the standard brain. All images show horizontal level at Z = −8 according to the atlas of Talairach and Tournoux (51). The Sokoloff color scale illustrates Z values (0.0–3.5 for AND and EST and 0.0–6.0 for OO). Because the same brain section is chosen, figures do not always illustrate maximal activation for each condition. The subject's right side is to the right. The right cluster in the lesbian woman plus HeW (Lesb+HeW) for AND − AIR did not pass the level of significance; the level of significance for the hypothalamic cluster for EST − AIR in Lesb+HeM was 0.06.