Desire and Arousability Sexual desire provides one of many motivations to be sexual. Feelings of desire may be triggered by both internal (e.g., fantasies, memories, feelings of arousal) and external (e.g., an interested and interesting partner). Sexual cues are dependent on adequate neuroendocrine function. Multiple neurotransmitters, peptides, and hormones modulate desire and subjective arousal (9). Substances that promote sexual response include norepinephrine, dopamine, oxytocin, melatonin, and serotonin acting on some receptors. Prolactin, serotonin acting on other receptors, endocannabinoids, opioids, and γ -aminobutyric acid inhibit sexual response. These peptides and neurotransmitters are themselves modulated by sex hormones that direct the synthesis of enzymes involved in the production of neurotransmitters and the synthesis of their receptors. Biological factors do not act independently from environmental factors, a finding in human and animal models. Dopamine and progesterone, acting on receptors in the hypothalamus, facilitate sexual behavior in female rats that underwent oophorectomy and received estrogen. The presence of a male animal in an adjacent cage can cause an identical change in sexual behavior (10). Likewise, the ability to be aroused and intensity of response can be increased in some women by giving them a modest dose of testosterone, by administering bupropion (dopaminergic), or by a change of partner (11–13). Even in rodents, complex networks exist whereby the female assesses the context of potential sexual activity and relates it to past experience and expectation of reward (14). In women, sexual interest is inﬂuenced by their psychological mindset, beliefs and values, expectations, sexual orientation, preferences, and the presence of a safe and erotic environmental setting. Empirical research confirms that an experimentally induced happy or sad mood can impact subjective sexual arousal (but not objective vaginal congestion as measured by a vaginal photoplethysmograph, a tamponlike photoelectric device placed in the vagina) while the woman views an erotic video, with subjects reporting significantly less subjective arousal and marginally significant fewer genital sensations when a negative mood was induced prior to viewing an erotic film clip (15). Moreover, other research concludes that cognitive factors (i.e., lack of erotic thoughts and being distracted or concerned about sexual behavior) were the best predictors of sexual desire: other dimensions including relationship factors, psychopathology, and medical problems appeared to have an indirect impact on sexual desire with the cognitive factors acting as the mediators (16). Sexual desire, interest, and arousability are most strongly inﬂuenced by mental health and feelings for the partner, both generally and specifically, at the time of sexual interaction (4,13,17,18). Sexual desire is strongly inﬂuenced by fatigue; as a result, sex late at night is not usually attractive to a busy woman. Similarly, chronic illness typically reduces desire and arousability (19).
Sexual Arousal Recent brain imaging reﬂects the complexity of sexual arousal, confirming that multiple areas of the brain are involved in sexual response. Brain imaging of healthy people during visual sexual stimulation identifies a model of sexual arousal involving complex brain circuitry, including cortical, limbic, and paralimbic areas known to be involved in cognition, motivation, and emotions linked to changes within the autonomic nervous system (20). Specific inhibitory regions deactivate these sexual responses (21). As demonstrated in this ongoing research, none of this is particularly simple. In a small study, sexually functional surgically menopausal women receiving no hormonal therapy viewed erotic videos during functional magnetic resonance imaging. The women failed to show the brain activation typical of premenopausal women and also typical of themselves when they were treated with both testosterone and estrogen, and yet, they reported sexual arousal from the erotic videos without, and with, hormonal supplementation (22).