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Features : Medical News Last Updated: Oct 19, 2011 - 9:13:37 AM

Kissing, teen brains, and advice and experience
By Steve Ferber
May 18, 2011 - 10:00:06 AM

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Kissing: nature or nurture?

Why do humans kiss? Is it a learned behavior or does it serve a primary function in evolution of the human species? In a 2011 issue of Discover Magazine, writer Sheril Kirshenbaum shared "20 things you didn’t know about kissing." Some highlights from Kirshenbaum’s findings:

· Kissing is not universal, points out Kirshenbaum, "leading some experts, like anthropologist Vaughn Bryant of Texas A&M to think that it might actually be a learned behavior."


· Citing the work of evolutionary biologist Claus Wedekind (Switzerland’s University of Lausanne), Kirshenbaum explains that "being close enough to kiss helps our noses assess compatibility." Wedekind’s study, said Kirshenbaum, "reported that women prefer the scents of men whose immunity-coding genes are different from their own. Mixing genes that way may produce offspring with a stronger immune system."


· A vote for nature? Said Kirshenbaum: ". . . two-thirds of all people turn their head to the right when kissing, according to psychologist Onur Gntrkn of Ruhr-University Bochum in Germany. This behavior may mirror the head-turning preference observed in babies and even in fetuses."


· Women vs. men? A study cited by Kirshenbaum found that "when deciding whether to kiss someone, women pay much closer attention than men do to the breath and teeth of their partner." The work cited was performed by evolutionary psychology Gordon Gallup (State University of New York, Albany).


Are teenage brains really different?

Actually yes, according to acclaimed science writer Carl Zimmer who in a recent article published in Discover Magazine posits that the teenage brain may fall into something of a "neurological gap" whereby their brain’s reward-seeking system is far more fully developed than their cognitive control network (which helps adults control their urges).

The short story, as Zimmer sees it: "The reward system of the teenage brain may make adolescents more willing to face the risks that come with this daunting new stage of life. But with access to modern dangers like illegal drugs and fast cars, the human risks have increased. Evolution does not operate quickly enough to have reacted to such factors. The brain’s heightened responses can also open the way for psychological troubles."

Zimmer says that research findings by neuroscientist B.J. Casey (who works with colleagues at the Sackler Institute of the Weill Cornell Medical College) suggest the following: "Due to experience, environment, or genes, some teens may possess relatively low levels of cognitive control, making them particularly vulnerable to neurological signals of fear. . . . If the signals go unchecked, they may lead to anxiety, depression, or other disorders such as addiction. And even well-adjusted adolescents may be primed to choose the heart over the head—or, perhaps we should now say, the ventral striatum" (the part of the brain that houses our reward-seeking system) "over the inferior frontal gyrus" (the part of the brain that houses our cognitive control network.

Some additional points raised by Zimmer:

· On the human reward-seeking system – citing Casey’s work, Zimmer explained: "The ventral striatum produces bigger responses to bigger rewards, and in teens it is rigged up to an amplifier, making rewards seem more appealing still."


· On the human cognitive control network – Zimmer said: "A separate network of regions in the front of the brain is responsible for evaluating conflicting impulses. This cognitive control network allows us to hold back an action that could deliver a short-term reward if it interferes with a long-term goal. The network grows very slowly over the first 25 years of life. As a result, it works poorly in childhood, better in teens, and even better in adults." Zimmer adds: "Casey proposes that as the cognitive control network matures, it gets more efficient. The upshot is that as we age, we need to put less effort into holding ourselves back."


· On the teenager’s "neurological gap" – explains Zimmer: "The trouble with teens, Casey suspects, is that they fall into a neurological gap. The rush of hormones at puberty helps drive the reward-system network toward maturity, but those hormones do nothing to speed up the cognitive control network. Instead, cognitive control slowly matures through childhood, adolescence, and into early adulthood. Until it catches up, teenagers are stuck with strong responses to rewards without much of a compensating response to the associated risks."


· The positive side of teenage urges – Zimmer continues: "From an evolutionary point of view, the daredevil impulses of adolescents can be beneficial, Casey points out. Once a young mammal becomes sexually mature, it needs to leave its parents and strike out on its own. It must find its own supply of food and establish its place in the world of adults. In some mammal species, adolescence is a time for individuals to leave one group and find a new one. In others, it is a time to seek out sexual partners.


Do you rely more on advice or experience?

It depends, say researchers, on your genetic makeup. A quick example: a good friend recommends that you buy some technology stocks, or recommends a certain car to buy. But you’ve had some negative personal experiences. Which way do you go? Do you rely on the advice, or your personal experience?

Apparently, it depends, in part, on your biological makeup, according to a new study out of Brown University. The researchers, according to David Orenstein, Life Sciences professor at Brown, "have found that specific genetic variations can predict how persistently people will believe advice they are given, even when it is contradicted by experience."

The study, reported last month in the Journal of Neuroscience, explored how two brain regions process incoming data. As Orenstein explains it: "The prefrontal cortex (PFC), the executive area of the brain, considers and stores income instructions such as the advice of other people (e.g., ‘Don’t sell those stocks.’) The striatum, buried deeper in the brain, is where people process experience to learn what to do (e.g., ‘Those stocks often go up after I sell them.’)

Orenstein, citing work by Michael Frank, Brown’s assistant professor of cognitive, linguistic and psychological sciences, explained: "It turns out that in a learning task, people are guided more by advice at the start. Their genes determine how long it takes before they let the lessons of experience prevail." Added Orenstein: "Like a ‘yes man’ who is flexible to a fault, the striatum would give more weight to experiences that reinforced the PFC’s belief, and less weight to experiences that contradicted it. Researchers call this confirmation bias, which is ubiquitous across many domains, such as astrology, politics, and even science."


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