Event-related potentials in males and females elicited by erotic pictures of females

Introduction: Stimulation with affective stimuli elicits event-related potentials (ERP), the area under the curve (AUC) correlating with „arousal“-values of these stimuli. The International Affective Picture System (IAPS) contains 716 pictures with different „arousal“-values (1 to 9), most of them identical (i.e. sports, food), some different (erotic pictures) for men and women. The aim of this study was to examine sex differences in the generation of ERP, elicited by pictures with large differences in the arousal-ratings in both sexes. Method: We examined 37 healthy subjects (20♀, 17♂), aged 25 (±1,9) years. ERP were elicited by three categories of pictures: sports, food and erotic females. Each category consisted of three pictures, taken from IAPS: category 1 („food“) had medium arousal values (4.5) for men and women, category 2 („sports“) had high arousal values (7) for both sexes and category 3 („females“) had high arousal values (7) for men and medium values (4.5) for women. All stimuli had medium or high values for „valence“ in both groups. ERP were analysed 500 ms pre-trigger and 1500 ms post-trigger from Fz, Cz, Pz, and from C3/C4 and P3/P4. Bandpass was 0.02 to 30Hz. Probes were sampled with 256Hz. Evaluation of the results was done by direct comparisons of the ERP (permutation test by Blair & Karniski), and by comparisons of the AUC. Results: i) In both groups, arousal ratings of the categories were as expected from given IAPS pictures. i) Between group comparisons of the ERP revealed no significant differences in all three categories. ii) Within group comparisons showed no significant differences between „sports“ and „food“. Nearly similar in both groups „females“ elicited significantly more positive ERP than „sports“ and „food“. Women even showed a tendency to generate larger AUC after „females“ than men. Conclusion: In contrast to our expectations and the different „arousal“-ratings in both sexes, erotic pictures of females did not result in significantly different ERP in men and women. This could be explained by social desirability: women consciously or unconsciously dissimulate the sexual arousal by erotic females. But ERP could also be influenced by different sexual and non-sexual arousing factors in men (i.e. sexual desire) and women (i.e. jealousy, envy, competition), summing up to similar ERP in both groups.