Watch The Truth about Female Desire online: Episode 4 The Big O

In this final programme in the series, the eight women are coming to the end of their intensive week of sexual self-discovery and putting their sex lives under the microscope. Tonight Dr John Bancroft, former head of the Kinsey Institute, helps them try and understand the nature and purpose of the female orgasm. One of the women takes part in a pioneering study being conducted by leading neuroscientist Dr Gert Holstege, becoming the first British woman to have a brain scan to find out what happens to the brain during sexual arousal and orgasm. Another of the girls volunteers to have blood taken whilst aroused to find out what hormones are active during orgasm. Dr Pierre Bouloux, who conducts the experiment, is genuinely amazed to find that the stress hormone adrenalin rose to levels more usually associated with a heart attack! At the end of the week of scientific endeavour, the women and scientists reflect on the unique experiment in which that they have taken part and discuss how much both parties have learnt from the experience.

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