What's Happening in the Brain
Sex drive, like the need to eat, is universal throughout all animal species. In humans, sexual behaviour is very complex and is usually coupled with a need for intimacy and for the favourable recognition of one's self by others. In consequence, there is no one "sexual activity" part of the brain. Sexual drive comes from structures known as the hypothalamus and pituitary gland. Self-realized sexual feelings, and the need to monitor one's expression of sexual activity, involve very highly developed parts of the brain. This is evident from studies of patients who have had damage to the front part of the brain. The part known as the orbitofrontal gyrus especially gives rise to a syndrome of disinhibited behaviour and inappropriate language and joking. This syndrome of saying and doing things that one should not do in the circumstances in which they are done can include inappropriate verbal and physical sexual behaviour.
More recent work on the brain structures that are involved in sexually inappropriate behaviour implicates other parts of the frontal lobes as well. These, in turn, are linked to subcortical areas, including some that are important in Parkinson's disease . Links between these brain structures and disinhibited behaviour have been detected by advanced brain imaging methods. They reinforce observations, from both drug treatment and surgical studies, that increasing the amount of the brain chemical dopamine can give rise to sexual disinhibition. This, in turn, provides insight into which drugs might be tried to treat inappropriate sexual behaviour. Even so, randomized controlled clinical trials of these drugs are lacking.