Motivation can be defined as a class of central nervous processes determining the likelihood of display of a behavior and the intensity of the behavior if displayed. All behavior is, according to this definition, caused and controlled by motivation. Although the concept of motivation eventually could be replaced by an entirely mechanistic explanation of the causes of behavior, in terms of neural events, such explanations would be overly complex for everyday use. This is particularly the case with regard to the momentaneous fluctuations in the intensity of a behavior, like those occurring during copulation in rats. Thus, the concept of motivation will remain useful even when mechanistic explanations become available. Even though the propensity to perform sexual responses is determined by sexual motivation, another element is required for the execution of such responses. This other element is an appropriate stimulus, a sexual incentive. For a male rat, an appropriate incentive could be a sexually receptive female. For a human, it could be a mental representation of a sexual partner. The incentive activates approach behaviors, and the intensity of these behaviors will be determined by motivation and by the quality of the incentive stimulus, its attractivity. Much work has been done with the purpose of identifying the nature of the incentive stimulus or stimuli emitted by rats and other mammals. While visual stimuli seem to be of limited importance, auditory and particularly olfactory stimuli have been found to have incentive properties. Soluble chemicals may be important for some aspects of copulation, but copulatory motor patterns are basically under the control of tactile stimuli. The processing of sexual incentives in the rat brain has been studied with electroencephalographic techniques, and data show that the prefrontal cortex (PFC) participates in the identification of sexual incentives. Furthermore, there are important differences between the medial and orbital frontal cortices. The medial PFC, as well as the ventral tegmental area, also seem to participate in the generation of pelvic thrusting.