The Brain and Sexuality

Genetics, psychological stress, and nutrition contribute to the age at onset of puberty. The average age at menarche is 12.75 years but it was much higher 150 years ago, when nutrition was poorer. The amount of fat stored in the body will help to determine whether puberty occurs in girls. It is believed that leptin, a hormone made by fat cells, helps to determine the age of menarche. Girls who are thin and active will have delayed menarche.

The secondary sex characteristics develop at the time of puberty. In males, these characteristics include increased laryngeal size, which deepens the voice, greater muscle development, and the growth of pubic hair, facial hair, and overall body hair. In females, it is increased fat deposition in the hip and breast area, increased breast size, and broadening of the female hips. Pubic and axillary hair develop. The growth spurt in girls happens prior to the onset of menarche with breast development being the first sign. In males, the first sign is the growth of the testes. The first fertile ejaculate happens at around 15 years of age.

THE BRAIN AND SEXUALITY

The brain is involved in all aspects of sexual behavior, from the onset of desire to orgasms and the need to cuddle. Researchers have done neuroimaging studies on human sexual behavior, which looks for the changes in the brain during sex in men and women. There is a four-component model that has been developed to try to understand the role the brain plays in sexual responsiveness.

The first stage is cognitive or the thinking phase. It involves the perception of the visual sexual stimulus, deciding if it causes sexual feeling. The ventromedial prefrontal cortex in the front of the brain is connected to the limbic system, which is the emotion system of the brain, as well as certain parts of the brain associated with the senses. The end result is the focusing of the attention toward the sexual stimulus, which activates both the occipital lobe, involved in vision, and the temporal lobe, involved with hearing. There is a specific extrastriate body in the brain that is connected to perceiving the human body.

The next stage is the emotional component, which involves mainly the limbic system. The amygdala is part of this system. It interacts with the ventromedial prefrontal cortex to control the processing of senses. The amygdala is highly connected to motivation so it helps to guide sexual behavior. Interestingly, if the amygdala is deactivated, this is what’s seen in patients who have indiscriminate sexual behavior and hypersexuality. Two of these syndromes are called Kluver syndrome and Bucy syndrome. The emotional part of this phase isn’t strictly so because it is also tight to the genitalia and the physical feelings of sexual pleasure.

The next stage is motivational, which is also highly dependent on the limbic system. Parts of the hypothalamus, thalamus, and anterior cingulate cortex get activated in this stage. This leads to the motivation toward reaching a sexual goal. Sexual urges, the need for reward, and sexual desires come at this time.

Lastly, there is the physical or physiological component. This involves hormonal changes, high blood pressure, racing heart, and genital responsiveness. Sexual arousal occurs to prepare the body for sex. This is all activated in the brain to generate the hormonal and autonomic responses to arousal. The hypothalamus is particularly important because it controls the parasympathetic and sympathetic nervous systems— two parts of the involuntary autonomic nervous system—which get activated during sex.

There are also inhibitory processes that help us control our sexual behavior so that not all urges are satisfied. If these processes are too activated, there may not be a gratifying sexual experience. If the anterior cingulate cortex and ventromedial prefrontal cortex are damaged, there can be the onset of excessive pleasure-seeking behavior that might be socially inappropriate.

In general, women have weaker brain responsiveness to visually erotic stimuli. While most researchers believe there are real differences in sexual brain activity and activation between men and women, these types of studies have not yet been done. Most studies have been done on heterosexual males and haven’t compared the two genders.

It appears that women are more complex when it comes to sex than men. Men more easily respond to visual sexual stimuli, when women have a stronger response to the sense of smell of their sexual partner. Women also respond more to erotic videos that