WE ARE OUR BRAINS - CHAPTER 4
PUBERTY, LOVE, AND SOCIAL BEHAVIOUR
The pituitary gland starts to produce sex hormones. The annoying behaviour, clashing with family members makes it less likely that reproduction takes place in their own surroundings, reducing the risk of inherited defects. Craving new experiences, readiness for great risks is leaving the nest behaviour. But since the PFC (prefrontal cortex) isn't yet mature, decisions may be bad, thinking about only the short term, and less consideration of negative consequences.
Gene KISS1 initiates puberty: kisspeptins produced in the hypothalamus.
Women must have enough fat to nourish a foetus in order to get pregnant.
Leptin is a hormone produced by fat cells. The brain monitors the levels of fat in the body by the amount of leptin. If there is a mutation in the leptin gene, the brain can block the onset of puberty and send out signals to make fat reserves: causing extreme obesity.
Melatonin, a hormone produced by the pituitary gland prevents puberty in children.
"Young people today love luxury, have bad manners, contempt for authority and disrespect for older people. They are to lazy to train, they'd rather sit and chat. They no longer rise when elders enter the room, they contradict their parents, can't hold their tongues in company, gobble up food, tyrannise their teachers. "
PFC: control of impulses, complex actions, planning, organisation. Doesn't fully mature until around 25 years of age.
Adults distribute assignments across different brain areas. Adolescent PFC have to work harder, and can't distribute, so their capacity is reached earlier, and distractions can undermine its performance.
The surge of sex hormones causes aggression and risk-seeking behaviour. They curve of crime rates follows that of PFC maturation.
Love: euphoria, a beating hard, perspiration, insomnia, emotional dependency, strongly focused attention, obsessive, possessive, protective attitude towards the partner, heightened energy.
Love, n. A temporary insanity curable by marriage.
Brain scans show activity in structures below the cerebral cortex. In the reward circuitry: addiction and withdrawal symptoms. Raised levels of the hormone cortisol. Testosterone levels rise in women, in men cortisone reduces testosterone production in testes.
Only when love has persisted for a certain amount of time, the PFC becomes involved.
The activity in the stress axis dies down and testosterone is normal. Only now can conscious choices be made for the first time.
Impulses caused by sex organ stimulation via the spinal chord reach the thalamus, centre for all erotic sensory information - to the ventral segmental area, the dopamine delivering reward circuitry - hypothalamus. If we orgasm, both dopamine and oxytocin are simultaneously released, nucleus accumbent for dopamine and oxytocin in the hypothalamus.
Orgasm activates the same reward pathways as heroin.
Different areas of the brain are activated in women and men during arousal - different sexes brains' use different routs to approach the same goal: orgasm.
Female: motor and sensory areas of the cerebral cortex are activated.
Male: occipital-temporal cortex, claustrum, insular cortex are activated. Periaqueductal grey matter is less activated in the brain stem, the same way as when addicts inject heroin.
The amygdala becomes less active in both sexes during orgasm, it usually inhibits sexual behaviour when we are supposed to be focused on something else.
Cerebellum - great increase in activity, it regulates muscle contractions of orgasm.
Prefrontal, Temporal Cortexes - less active, reduce inhibitions during sex.
DNA polymorphisms in the protein that receives dopamine's chemical message are correlated to the degree of sexual desire, arousal, activity.
Testosterone promotes women's and men's sexual drive. That's why it declines in older men with less testosterone. Women who's adrenal gland and ovaries produce more are more sexual.
Around ovulation, women subconsciously dress more provocatively, get tipped more, prefer more masculine faces, voices and behaviour.
Erotic images provoke greater stimulation in the brains of young men vs those of young women.
Women's degree of activation of the amygdala and hypothalamus to sexual stimulation also depends on their stage of menstrual cycle, being highest around ovulation and lowest during menstruation.
Oxytocin, produced in the hypothalamus and released visa the pituitary gland is important during sex.
In men, it stimulates contraction of smooth muscle fibres, facilitating sperm transport.
In women, it sends sperm one way and the egg another way to encounter one another. Because oxytocin is important in sperm transport, a partner who induces orgasm for the female has an evolutionary advantage.
Oxytocin also promotes pair forming. It inhibits the stress system and causes opiates to be released in the brain.
Depression lowers sex drive. The dopamine reward system is inhibited by high cortisol levels, and all pleasure in life can be gone: anhedonia. Testosterone levels decline. Antidepressants also lower libido and inhibit orgasm.
Diabetics can suffer from sexual dysfunction as a result of damage to nerve fibres. Diabetes is the most common cause of erectile dysfunction in men and painful intercourse in women.
Men with full spinal chord injury (paraplegia or quadriplegia) cannot have erections caused by the brain: seeing, felling smelling. But they can still have stimulation of the penis erections because those travel through the lowest part of the spinal chord.
In able-bodied people, psychogenic erections start in the brain and erotic impulses travel up from the spinal chord. They go up and own. But 38% of paraplegics still orgasm.
1) For some paraplegics the skin near the site where the loss of feeling starts become so hypersensitive, it turns into a new erogenous zone, which can be stimulated to orgasm.
2) In women injured above the navel, the impulses were sent via the cranial/vagus nerve to the brain.
3) Nerve cells low in the spinal chord take over functioning as the ejaculation centre.
Some epileptics feel as though they are having orgasms before seizures.