Brings a whole new meaning to the calendar method. Always knew the male of the species was being short-changed here (dons the helmet and flak jacket whilst hastily explaining swis is only referring to climactic pleasures and not life in general). This from The Telegraph (UK): Why women enjoy sex more on certain days By Roger Highfield, Science Editor Last Updated: 1:08am GMT 05/02/2007 Monthly mood swings may help women to get pregnant, according to a new study. A team of US scientists have discovered that fluctuations in levels of the female sex hormone oestrogen affect the responsiveness of the brain's "reward system", with a peak in the first part of the menstrual cycle. This reward system dictates the amount of pleasure attained from various activities, whether it be from having sex or from eating chocolate. "Increased activity of the brain's reward system at this time could boost anticipation and enjoyment of sexual activity," said Dr Karen Berman of the US National Institute of Mental Health, who worked on the study published in the Proceedings of the National Academy of Sciences. "This demonstrates for the first time that female hormones affect the reward system in very specific ways during particular parts of the cycle," added Dr Berman, who went on to stress that the results did not mean that women are more emotional or vulnerable to hormones than men. The study looked at women playing an imaginary slot machine game, and showed their brain responses changed in anticipation of a payout depending on the phases of their menstrual cycles. For instance, four to eight days after menstrual bleeding started, the orbiofrontal cortex and amygdala of the brain were more active. This might help explain other studies that show women get a bigger kick from cocaine and amphetamines during the earlier stage of their fertility cycle, the researchers added. In addition, it may lead to insights into why women are less vulnerable to schizophrenia than men.