Motivation: motivation refers to the moving force that energizes behavior. Eating: hypothalamus receives information regarding nutrient levels in body. Lateral region: stimulation induces eating, lesions of the lateral region produce starvation. Ventromedial region: lesions induce overeating, stimulation inhibits eating. Organizational effects: prenatal exposure to androgens alters the neural circuits in brain and spinal cord, adult behavior of androgenized subject is masculine. In the absence of androgens, nature"s impulse is to create a female . Activational effects: alteration of adult levels of hormones can alter the intensity of a behavior that is modulated by that hormone: pheromones, environmental cues. Sexual behavior: parental investment, patterns of sexual activity, differences in mate preferences, jealousy. Sexual orientation: sexual orientation is the direction of attraction for a sexual partner. Homosexuality: attraction for a person of the same-sex: twin studies document a biological basis for homosexuality, hormonal responses differ between homosexual and heterosexual men. Fig 10. 13 homosexuality and heterosexuality as endpoints on a continuum.