Sexual repsonse regulation. Level of sexual motivation, as well as that of thirst and hunger, can be changed by damage to or stimulation of certain areas of the hypothalamus (including the medial preoptic area and the VMH) and other portions of the brain (such as the limbic system). Sexual behavior is also affected by levels of the sexual hormones—primarily, testosterone in males and estrogens in females—produced by the gonads. Sexual hormone production in the gonads is, in turn, controlled by hormones produced in the pituitary gland. Sexual behavior is complex, however, and may be affected by many factors, particularly during development, such as administration of sex hormones or ingestion of drugs that affect production of sex hormones.
The sexual response cycle. William Masters and Virginia Johnson described the sexual response cycle in both females and males as comprising four phases:
excitement: initial arousal of genital areas
plateau: continued excitement, increasing rates of breathing and pulse, and increasing blood pressure
orgasm: rapid contraction of muscles in genital area, release of semen by male, feeling of pleasure by both genders
resolution: return of body to an unaroused state
Sexual dysfunction. Some individuals experience difficulties in one or more of the sexual response phases. Such problems and other sexual dysfunctions are of concern to those psychologists working with behavior problems. Problems include, among others, premature ejaculation and impotence (inability to be physically aroused) in males and inability to experience orgasms (organismic dysfunction) and low sexual desire in females.
Sexual orientation. Sexual orientation refers to the direction of one's erotic interests. Heterosexuals are attracted to people of the opposite gender; homosexuals (gay males and lesbian females) are attracted to people of the same gender; bisexuals are attracted to members of either gender. Differences in sexual orientation exist in all cultures. Most psychologists today tend to view sexual orientation as a characteristic of human behavior that is neither willfully chosen nor willfully changed; people are born one way or another. A 1996 survey found that 3.5% of the men and 2.1% of the women reported having had a homosexual experience within the past 12 months. Sexual orientation is not linked to any type of psychological disorder or sexual crime (such as child molestation). Homosexuality was dropped as a “mental illness” by the American Psychiatric Association in 1973.