Any behaviour that increases sexual excitement and SEXUAL AROUSAL or fulfils sexual desires. Sexual behaviour may be viewed in terms of appetitive responses that increase sexual excitement and bring animals into contact with sexually-relevant stimuli or sexually receptive partners, and consummatory responses such as masturbation or copulation, that serve to fulfil sexual desire. Although sexual behaviour plays an obvious role in REPRODUCTION, it also serves other functional endpoints, such as PLEASURE and REWARD. In fact, many ‘inappropriate’ appetitive and con-summatory sexual responses can be conditioned by sexual reward.
For all animals, sexual behaviour occurs as a sequence or cascade of behavioural events. For copulation to occur at all, animals must be capable of responding to a variety of internal and external cues. They must be able to respond to hormonal and neurochemical changes that signal their own sexual excitement, arousal, and receptivity, to identify external stimuli that predict where potential sex partners can be found, to actively seek out or work to obtain sex partners, to distinguish pheremonal cues (see PHEROMONES) or behavioural patterns of potential sex partners from those that are not sexually receptive and to attract, solicit and pursue desired sex partners once contact has been made. Most of these appetitive responses occur before copulation is initiated and can be used to make inferences concerning such motivational variables as SEX DRIVE, LIBIDO, sexual arousal and desire, distinct from copulatory performance. An animal’s ability to perform these responses requires a great deal of behavioural flexibility and the capacity to learn which stimuli or responses are the most predictable or efficacious, respectively. In fact, such learning may play an important role in the development of sexual preferences and erotic orientation.
Once contact is made, animals engage in more stereotypic, species-specific and gender-specific patterns of copulation. An exception to this is humans, in which there are no real gender-specific copulatory behaviours (except those that are culturally based). In species in which the females display ESTRUS cycles, copulation is typically under the complete control of the female. In such species, females do not show sexual receptivity until they are in behavioural estrus or HEAT, when ovarian steroids have activated the appropriate neurochemical systems and neuroanatomical pathways for FEMININE sexual behaviour (for instance in the MEDIAL PREOPTIC AREA and VENTROMEDIAL HYPOTHALAMUS). Females in estrus attract, solicit and pace the rate of sexual contact with desired males, which in turn, provides them with the requisite type of sexual stimulation (for example, vaginocervical stimulation) necessary to promote PREGNANCY if insemination occurs. In contrast, males will pursue, mount and intromit (see INTROMISSION) one or more receptive partners in a seemingly non-discriminatory fashion until they become sexually exhausted (for example, from repeated ejaculations) or the females terminate estrus. However, males of some mammalian species (rodents for example) are capable of learning to direct their ejaculations to females that bear conditioned extroceptive cues (such as odours). For males, consummatory copulatory responses are under the control of testicular steroids which maintain the integrity of peripheral sex organs and activate the appropriate neurochemical systems and neuroanatomical pathways for MASCULINE sexual behaviour. In males of many species, the aromatization (see AROMATIC) of androgens into estrogens within certain brain regions (for instance, medial preoptic area) is crucial for copulatory responses to occur because estrogen activity in these regions promotes masculine copulatory responses. However, some male primates retain masturbation following castration long after copulatory responses have declined. Even in egg-laying species in which fertilization occurs externally, males often make contact with females (which in some cases helps to promote egg-laying) prior to ejaculation. Interestingly, in some parthenogenetic females (certain whiptail lizards for instance; see PARTHENOGENESIS) ‘male’ copulatory stimulation (for example mounting and clasping) by another female CONSPECIFIC is necessary to promote ovulation and self-fertilization.
Sexual reward shares many features of drug reward. Copulation activates the MESOLIMBICOCORTICAL SYSTEM in male rats in a manner similar to low, self-administered doses of AMPHETAMINE. Ejaculation in male rats also induces the release of endogenous opioids, and promotes HIPPOCAMPAL THETA rhythm, SLEEP, the modulation of PAIN, and the reduction of ANXIETY. Although intromissions alone are capable of sustaining the development and maintenance of copulatory responses in male rats, ejaculation appears necessary for the development of certain conditioned sexual responses and unconditioned parental behaviours. Until recently, there has been little evidence that females of many species find sexual behaviour rewarding. Although ovarian steroids facilitate appetitive sexual responses in females, certain types of sexual stimulation (for instance vaginocervical stimulation) lead to a faster termination of both appetitive and consummatory sexual behaviour. However, female rats show a CONDITIONED PLACE PREFERENCE for distinctive environments in which they can pace the copulatory contact, compared to other environments in which they cannot. In contrast, some female primates are capable of ORGASM and appear to derive as much pleasure and reward from it as males do.
