In the present study we investigated the neural correlates of erotic processing in healthy female volunteers taking oral contraceptives as compared to women in early follicular or mid-luteal phase (not taking contraceptives). Direct erotic stimulation with either dynamic videos or static pictures induced significant brain activation in a set of brain regions which has already been described by previous studies using comparable erotic stimuli 
. Interestingly, this rather direct confrontation with explicit visual erotic stimuli at given thresholds was only associated with few differences in quite distinct brain regions between the different hormonal states and under oral contraceptives. Only in the bilateral inferior part of the precentral gyrus the nC group in its follicular phase demonstrated higher activation when compared against the C group.
A different pattern emerged for less direct erotic stimulation, experimentally induced by investigating brain activation upon expectation of static erotic stimuli. This experimental condition was associated with considerably less anatomical overlap of activated brain regions across the different hormonal states. Instead, activation differences already emerged when comparing the nC group at its different phases. Group differences were most pronounced when comparing the nC group during both hormonal states against the C group. Among the various brain regions showing either within- or between-group differences, the dorso-medial prefrontal cortex consistently emerged in three different contrasts comparing the luteal against the follicular phase in the nC group, and also when comparing both phases against the C group. Across tasks (video stimulation, expectation of erotic pictures), the inferior pre-central gyrus was consistently more activated in the nC group during its follicular phase than in the C group.
Women’s interest in visual sexual stimuli has been shown to be modulated by hormonal states 
. In a study using eye-tracking methods to measure eye movements to different aspects of erotic pictures, it was observed that women who did not take oral contraceptives spent more time looking at genitals whereas women with oral contraceptives focused more on contextual details such as clothing or background 
The rationale for the present study was to further investigate these effects of different hormonal levels corresponding to the mid-follicular and mid-luteal phase of the menstrual cycle and during oral contraception. A better understanding of possible hormonal moderators of the neural correlates of erotic stimulation in women may help to understand other influences such as processing of erotic stimuli under different anti-depressants. From the present results it appears that different hormonal levels do exert only minor effects on these neural correlates when visual erotic stimulation is rather direct and explicit. Particularly, subcortical regions that were most affected by antidepressant treatment in males 
did not show marked differences associated with different hormonal levels. We therefore conclude that in comparison to psychotropic drugs that are known to affect sexual arousal such as SSRI antidepressant drugs, oral contraceptives have much weaker effects, and women taking contraceptives may be well suited for pharmaco-fMRI trials as long as erotic stimulation is direct and explict. Also the absence of differences in subjectively rated sexual functioning adds to this conclusion. It is of note, however, that from the effects related to the two phases of the menstrual cycle investigated in the present study, no conclusions can be drawn regarding effects around ovulation. Because of the inconsistent results concerning brain activation around the ovulatory phase 
, we decided to assess female brain activation related to sexual stimulation at two time points clearly apart from ovulation and compare these to the activation under oral contraceptives.
While brain activation upon direct visual erotic stimulation was not markedly affected by different hormonal levels this appears not to be the case when expectation of erotic stimuli was induced as a separate condition. For this condition significant hormonal influences on activated brain regions were observed. However, it remains unclear whether these differences indicate a state of reduced sexual appetence under hormonal contraceptives since results from previous studies also have demonstrated effects of contraceptives on brain activation during a pure cognitive task (verb generation task; 
). Interestingly though, highly significant cortical group differences between the C group and the nC group were most pronounced when comparing effects of contraceptives with those in the mid-follicular phase on expectation of erotic pictures. Since increasing brain activation upon erotic stimulation has been related to rising estrogen levels during the follicular phase 
and also under hormonal replacement 
, these differences may still relate to reduced sexual appetence under oral contraceptives.
This interpretation is further supported by the bilaterally reduced activation of the pre-central gyrus under oral contraception, that was evident during both the dynamic video stimulation and the picture expectation task when compared against the nC group mid-follicularly. The precentral gyrus is a brain area with a high density of estrogen receptors 
and has greater relative volume in women than in men 
. In men, activation of the pre-central gyrus has already been related to measures of penile turgidity under erotic vs. non-erotic visual stimulation 
. In a study on the relationship of women’s preference for masculine traits and phases of the menstrual cycle, greater responsiveness of the pre-central gyrus was found for masculine faces during the follicular phase 
. Together with the posterior cingulate cortex, pre-central gyrus activation has also been associated with scores of sexual inhibition, and the authors of that study identified the pre-central gyrus as one of the brain regions associated with behavioural inhibition and self-awareness in wider contexts 
. Furthermore, the posterior cingulate cortex but also the pre-central gyrus have been shown to be involved in mental simulation of actions 
and self-recognition 
. In addition to our present observation these results suggest that the pre-central gyrus may have something to do with the self-related anticipation of a sexual action. Its decreased activation under hormonal contraceptives may therefore indicate a decreased motivation or drive towards sexual activity under these drugs. Similar interpretations may apply for the adjacent differential insular activations that partially overlapped with precentral clusters for the same contrast. Particularly the left-sided insula has been related to mental representations of subjective pleasure upon sexual experiences in women 
Although as a statistical trend (contrasts survived uncorrected but not corrected thresholds), the oral contraceptive group’s activation upon expectation of erotic stimuli was reduced compared to mid-luteal nC subjects in two additional brain regions, the dorsomedial prefrontal cortex (DMPFC) and anterior middle cingulate cortex. Using the same picture stimuli as in the present study, DMPFC activation upon erotic stimulation has been repeatedly reported in previous studies 
. Although particularly anterior parts of the DMPFC could be linked to the processing of erotic stimuli, those previous data favoured a more general role of this region in the context of attending to mental states or processing of socially relevant stimuli, particularly those with high self-relevance 
. By contrast, involvement of the anterior middle cingulate cortex appears to rely more specifically on sexual stimulation, since activation of this region was correlated with penile tumescence as shown by recent studies using positron-emission tomography 
, fMRI 
, and arterial spin labelling measures 
Regarding limitations to our study, the actual sample size of 12 subjects per group may confine generalizability of the results. Also, we did not obtain objective measures of sexual arousal and functioning. Thus we could not objectively infer effects of contraceptives on sexual functioning in women, beyond subjective rating data. Therefore, while our experimental data may allow for inferences regarding hormonal effects on brain responsivity upon erotic stimulation, the relation to actual sexual functioning should be subject to further investigations. Furthermore, the video material used was most likely produced for a male audience and was implemented for reasons of comparability with the results of our previous studies. Currently, we cannot answer the question of how brain activation in female brains would compare to present results if the video material had been tailored specifically for a female audience.
Taken together, different hormonal states along the menstrual cycle or the intake of oral contraceptives predominantly modulated activation of cortical brain regions upon expectation of erotic stimuli. During direct and explicit erotic stimulation, either by dynamic videos or static pictures the effects of hormonal influences appeared to be comparably weak. Most likely, the strong overall effect of this kind of erotic stimulation may suppress subtle effects of different hormonal states during menstrual cycle or under oral contraceptives and hormonal effects on brain activation during direct and explicit erotic stimulation may not interfere with stronger influences such as medical conditions or psychotropic drugs. We therefore conclude that each of the hormonal states investigated can be selected to study psychopharmacological effects on brain activation during erotic stimulation as long as all women under investigation adhere to the same hormonal state. It is of note, however, that it should not be concluded from present data that different hormonal states can be pooled within one sample.