Saturday, 17 June 2006

Brains, Hormones, and Erotica

Some of the latest news in the "Undiscovered Country", our own neurology.

From EMaxHealth :
Researchers at Washington University School of Medicine in St. Louis measured brainwave activity of 264 women as they viewed a series of 55 color slides that contained various scenes from water skiers to snarling dogs to partially-clad couples in sensual poses.
As subjects looked at the slides, electrodes on their scalps measured changes in the brain's electrical activity called event-related potentials (ERPs). The researchers learned that regardless of a picture's content, the brain acts very quickly to classify the visual image. The ERPs begin firing in the brain's cortex long before a person is conscious of whether they are seeing a picture that is pleasant, unpleasant or neutral.

But when the picture is erotic, ERPs begin firing within 160 milliseconds, about 20 percent faster than occurred with any of the other pictures. Soon after, the ERPs begin to diverge, with processing taking place in different brain structures for erotic pictures than those that process the other images.
A great deal of past research has suggested that men are more visual creatures than women and get more aroused by erotic images than women. Anokhin says the fact that the women's brains in this study exhibited such a quick response to erotic pictures suggests that, perhaps for evolutionary reasons, our brains are programmed to preferentially respond to erotic material.

"Usually men subjectively rate erotic material much higher than women," he says. "So based on those data we would expect lower responses in women, but that was not the case. Women have responses as strong as those seen in men."

Because the electroencephalogram (EEG) technology cannot pinpoint specific brain structures involved in this visual processing, Anokhin says it's not clear exactly which circuits are reacting to these visual scenes. Recent studies in primates recorded the electrical activity of single neural cells within the brain and have shown that the frontal cortex contains neurons that can discriminate between different categories of visual objects such as dogs versus cats. Whether or not the human prefrontal cortex contains special neurons that are "tuned" for sex remains a subject for future studies.
So the well-established difference in the way men and women perceive erotica appears to be in the "back-end" processing. The initial perception mechanisms appear to be the same.

From ScienceCentral :
Becoming a father tends to change a man's outlook, but now scientists are showing it might also change his brain. This ScienCentral News video explains that new research in father mice reveals how time spent with their young benefits the brain.
Lambert's research on mother rats has provided mounting evidence that motherhood benefits the brain. She found that mom rats do better on learning and memory tests than non-moms, and are also bolder, suggesting that they are protected against the damaging effects of stress.

Lambert linked these changes to the flood of hormones that accompany pregnancy and lactation, but as she wrote in Scientific American magazine, even non-mom rats given "foster" pups showed changes in these areas. Lambert got interested in the possibility that the same could be true for rodent dads. Her most recent experiments show that dads actually do outperform bachelors of the same species at locating food and show less stress in new situations, such as when encountering unfamiliar objects.
They looked for changes in two hormones known to be involved in nurturing and social behaviors: oxytocin, often nicknamed the "cuddle hormone," which is important in maternal bonding, and vasopressin, which is thought to be important in social behaviors in males.

Vasopressin is also hypothesised as being implicated in the 50% of male-to-female transsexuals whose sexual orientation changes 6 months after testicular removal or dysfunction.

From :
Field biologists have noted that the male prairie vole pairs off with a single female, probably for life. Neuroscientists have long wondered what keeps these males content with one mate while their close cousins, the montane voles, exhibit a more, shall we say, promiscuous dating style. While the stay-at-home prairie voles cuddle in their burrows, montane males mate indistriminately with one female after another.

This vast difference in lifestyle may come down to a single brain hormone, vasopressin, which in the human body is more commonly associated with regulation of water content. Research indicates that vasopressin induces the male prairie vole to stay with and protect his mate.

At the same time, vasopressin may trigger another characteristic behavior--that of the father prairie vole caring for his pups, another group of investigators finds.
Both vasopressin and oxytocin consist of short chains of amino acids. In their role as traditional mammalian hormones, they are secreted by the peasized pituitary gland and can take miniutes to exert their effects. Vasopressin stimulates absorption of water by the kidneys and thus decreases urine flow. Oxytocin plays a role in many reproductive functions, such as the contractioN of the uterus during labor.

However, these chemicals are also synthesized by specialized nerve cells in the hypothalamus and other parts of the brain. In their role as brain hormones, they transmit messages between nerve cells in the brain, a process that takes only a fraction of a second. As fast-acting chemical messengers, oxytocin and vasopressin must each approach and dock with its own proteiN receptor on a target nerve cell. Once the docking is complete, each chemical triggers a cellular response.
There's a lot of uncertainty about the implications of these findings. De Vries speculates that vasopressin may act as a master switch in the brain. Researchers know that vasopressin released by the pituitary finetunes the body's water content and blood pressure. And recent work by Insel, De Vries, and others suggests that prairie voles, and perhaps other mammals, have co-opted this brain hormone to govern a host of complex behaviors.
"Making the jump from vole to human is dangerous at best," Winslow says, noting that voles are virtually slaves to their brain chemistry. Humans, on the other hand, experience environmental and cultural influences that appear to play a large role in their sexual and parenting behaviors.

And finally, from :
Women whose oxytocin levels rose in response to massage and remembering a positive relationship reported having little difficulty setting appropriate boundaries, being alone, and trying too hard to please others. Women whose oxytocin levels fell in response to remembering a negative emotional relationship reported greater problems with experiencing anxiety in close relationships.

"It seems that having this hormone "available" during positive experiences, and not being depleted of it during negative experiences, is associated with well-being in relationships," said Turner.

In addition, women who were currently involved in a committed relationship experienced greater oxytocin increases in response to positive emotions than single women. The researchers speculate that a close, regular relationship may influence the responsiveness of the hormone, said Turner.

These preliminary findings bring up some intriguing questions, said Teresa McGuinness, MD, PhD, UCSF clinical psychiatry faculty member and co-author of the paper. Because oxytocin is released in men and women during sexual orgasm, it may be involved in adult bonding, said Turner. There is also speculation that in addition to facilitating lactation and the birthing process, the hormone facilitates the emotional bond between mother and child.

"Evolutionarily speaking, it makes sense that during pregnancy and the postpartum, both a woman's body and her mind would be stimulated to nurture her child," said Turner.

Oxytocin may also play a role in the higher levels of depression and interpersonal stress seen in women, said Turner. According to most psychiatrists, women experience depression twice as often as men and tend to be more affected by relationship difficulties. Turner and her colleagues hope that their work on oxytocin will guide future research on the psychiatric conditions of men and women.

"Our results provide the groundwork for further studies looking at the way hormones may be affecting human attachment," said Turner. "We know that oxytocin is one of the hormones that can facilitate bonding in other animals, but this is the first step in exploring whether it plays a role in the emotional behavior of humans."

If you think there's an awful lot about the way that the brain works, and the effect of these lesser-known hormones, that we haven't got a clue about... then you're right.

That's not especially comforting for someone who is aware that those levels are changing even as they write a blog entry, and that their mind is being affected by that.

Oh well, it's not as if I can actually do anything about it. Accept, roll with the punches, and try to record subjective and difficult to measure data as best I can. And try not to worry about it too much. Changes can just as easily be for the better as the worse, and often they're neither, they're just changes. We, unlike voles, are not slaves to our hormones, merely strongly influenced by them.

Though try telling that to someone whose partner has PMT.... it's always easier to observe from the outside, rather than live through the experience. Well, easier from a Scientific viewpoint, anyway.

Now where's that chocolate?

No comments: