Tag Archives: prefrontal cortex

‘Love’ hormone oxytocin regulates female sexual behavior, study suggests

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Previous research shows that the hormone oxytocin stimulates social behavior in humans, but a study published Thursday in the journal Cell suggests the hormone plays an especially strong role in regulating female sexual behavior.

Scientists at The Rockefeller University in New York City genetically modified female mice so that they no longer had an oxytocin response in the prefrontal cortex. As a result, the females no longer approached male mice for mating during the sexually receptive stage of their estrous cycle. In fact, with reduced oxytocin, the female mice showed about as much interest in males as they did in a LEGO block.

The researchers manipulated only a small amount of the neurons— less than 1 percent in the prefrontal cortex, an area known to trigger behavior in mammals, lead author Miho Nakajima, a graduate student at The Rockefeller University, told FoxNews.com.

Senior study author Nathaniel Heintz, a James and Marilyn Simons professor at The Rockefeller University, said the female mice were still interested in males and other females when oxytocin was reduced, but they didn’t show sexual interest.

“When [female] mice are sexually active, this small population [of neurons] is required for female mice to show interest in the male mice,” Heintz, an investigator at Howard Hughes Medical Institute, told FoxNews.com.

Researchers found that the change in interest among the male mice was less pronounced than the females’ response when researchers manipulated their oxytocin levels.

“There’s a functional difference in how male mice and female mice responded,” Heintz said.

Past research has shown that oxytocin plays a strong role in partner and mother-child bonding.

A study previously published in the journal Psychoneuroendocrinology showed that oxytocin levels skyrocket when people fall in love, and that a higher amount of oxytocin is correlated with longer relationships. Another study, in the journal Social Cognitive and Affective Neuroscience, suggested that oxytocin improved communication and lowered cortisol, a stress hormone, in both men and women. Many scientists have consequently nicknamed oxytocin the “love” or “pro-social” hormone.

The study authors said further research should explore what oxytocin does at a molecular level, and which brain areas and what types of cells respond to the hormone. Their study explores how oxytocin behaves in just one context.

Other studies have examined whether oxytocin levels can be modified to enhance the social behaviors of people with autism spectrum disorder (ASD). The mental condition impacts 1 in 68 children, and its hallmark is impaired social interaction.

Heintz said his team’s findings could help advance treatment development for ASD.

A study published last year in the journal Proceedings of the National Academy of Sciences suggested that a single dose of oxytocin can increase brain functions responsible for social interaction in children and adolescents with autism. In their research, Yale University scientists found that brain centers associated with reward and emotional cognition responded more during social tasks when the study participants were giving an oxytocin nasal spray rather than a placebo nasal spray.

“Each study gives us more insight into how this [oxytocin] might be acting in humans,” Heintz said.

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Breaking New Year’s Resolutions – The Neuroscience Explanation

Blame It on the Brain

The latest neuroscience research suggests spreading resolutions out over time is the best approach

By

Jonah Lehrer

Updated Dec. 26, 2009 12:01 a.m. ET
Willpower, like a bicep, can only exert itself so long before it gives out; it’s an extremely limited mental resource.

Given its limitations, New Year’s resolutions are exactly the wrong way to change our behavior. It makes no sense to try to quit smoking and lose weight at the same time, or to clean the apartment and give up wine in the same month. Instead, we should respect the feebleness of self-control, and spread our resolutions out over the entire year. Human routines are stubborn things, which helps explain why 88% of all resolutions end in failure, according to a 2007 survey of over 3,000 people conducted by the British psychologist Richard Wiseman. Bad habits are hard to break—and they’re impossible to break if we try to break them all at once.

James Steinberg

Some simple tricks can help. The first step is self-awareness: The only way to fix willpower flaws is to know about them. Only then can the right mental muscles get strengthened, making it easier to succeed at our annual ritual of self-improvement.

The brain area largely responsible for willpower, the prefrontal cortex, is located just behind the forehead. While this bit of tissue has greatly expanded during human evolution, it probably hasn’t expanded enough. That’s because the prefrontal cortex has many other things to worry about besides New Year’s resolutions. For instance, scientists have discovered that this chunk of cortex is also in charge of keeping us focused, handling short-term memory and solving abstract problems. Asking it to lose weight is often asking it to do one thing too many.

In one experiment, led by Baba Shiv at Stanford University, several dozen undergraduates were divided into two groups. One group was given a two-digit number to remember, while the second group was given a seven-digit number. Then they were told to walk down the hall, where they were presented with two different snack options: a slice of chocolate cake or a bowl of fruit salad.

Here’s where the results get weird. The students with seven digits to remember were nearly twice as likely to choose the cake as students given two digits. The reason, according to Prof. Shiv, is that those extra numbers took up valuable space in the brain—they were a “cognitive load”—making it that much harder to resist a decadent dessert. In other words, willpower is so weak, and the prefrontal cortex is so overtaxed, that all it takes is five extra bits of information before the brain starts to give in to temptation.

This helps explain why, after a long day at the office, we’re more likely to indulge in a pint of ice cream, or eat one too many slices of leftover pizza. (In fact, one study by researchers at the University of Michigan found that just walking down a crowded city street was enough to reduce measures of self-control, as all the stimuli stressed out the cortex.) A tired brain, preoccupied with its problems, is going to struggle to resist what it wants, even when what it wants isn’t what we need.

There’s something unsettling about this scientific model of willpower. Most of us assume that self-control is largely a character issue, and that we would follow through on our New Year’s resolutions if only we had a bit more discipline. But this research suggests that willpower itself is inherently limited, and that our January promises fail in large part because the brain wasn’t built for success.

Everybody knows that the bicep has practical limitations: If we ask the muscle to hold too much, it will give out and drop everything on the floor. And just as our muscles get tired after a tough workout, and require a rest to recuperate, so does the poor prefrontal cortex need some time off.

In a 2002 experiment, led by Mark Muraven at the University at Albany, a group of male subjects was asked to not think about a white elephant for five minutes while writing down their thoughts. That turns out to be a rather difficult mental challenge, akin to staying focused on a tedious project at work. (A control group was given a few simple arithmetic problems to solve.) Then, Mr. Muraven had the subjects take a beer taste test, although he warned them that their next task involved driving a car. Sure enough, people in the white elephant group drank significantly more beer than people in the control group, which suggests that they had a harder time not indulging in alcohol.

The implications of this muscle metaphor are vast. For one thing, it suggests that making lots of New Year’s resolutions is the wrong way to go about changing our habits. When we ask the brain to suddenly stop eating its favorite foods and focus more at work and pay off the Visa…we’re probably asking for too much.

The willpower-as-muscle metaphor should also change the way we think about dieting. Roy Baumeister, a psychologist at Florida State University who has pioneered the muscle metaphor, has demonstrated in several clever studies that the ability to do the right thing requires a well-fed prefrontal cortex.

In a 2007 experiment, Prof. Baumeister and his colleagues found that students who fasted for three hours and then had to perform a variety of self-control tasks, such as focusing on a boring video or suppressing negative stereotypes, had significantly lower glucose levels than students who didn’t have to exert self-control. Willpower, in other words, requires real energy.

In another experiment, Mr. Baumeister and his colleagues gave students an arduous attention task—they had to watch a boring video while ignoring words at the bottom of the screen—before asking them to drink a glass of lemonade. Half of the students got lemonade with real sugar, while the other half got a drink with Splenda. On a series of subsequent tests of self-control, the group given fake sugar performed consistently worse. The scientists argue that their lack of discipline was caused by a lack of energy, which hampered the performance of the prefrontal cortex.

Since the most popular New Year’s resolution is weight loss, it’s important to be aware that starving the brain of calories—even for just a few hours—can impact behavior. Skipping meals makes it significantly harder to summon up the strength to, say, quit cigarettes. Even moderation must be done in moderation.

The final piece of the willpower puzzle is distraction. Research by Walter Mischel at Columbia University and others has demonstrated that people who are better at delaying gratification don’t necessarily have more restraint. Instead, they seem to be better at finding ways to get tempting thoughts out of their minds.

For instance, Prof. Mischel has found that four-year-old children who are better at resisting the allure of eating a marshmal low—they get a second marshmallow if they can wait for 20 minutes—are the ones who sing songs, play with their shoelaces or pretend the marshmallow is a cloud. In other words, they’re able to temporarily clear the temptation out of consciousness. (Prof. Mischel has also shown that these “high delayers” go on to get higher SAT scores and have lower body-mass indexes as adults.) Because they know that willpower is weak, they excel at controlling the spotlight of attention: When faced with candy, they stare at the carrots.

While this willpower research can get dispiriting—the mind is a bounded machine, defined by its frailties—it also illustrates some potential remedies. Prof. Baumeister figured that it might be possible to strengthen willpower by exercising it, and in 1999, he asked a group of students to improve their posture for two weeks. Interestingly, these students showed a marked improvement on subsequent measures of self-control, at least when compared to a group that didn’t work on sitting up and standing straight.

The lesson is that the prefrontal cortex can be bulked up, and that practicing mental discipline in one area, such as posture, can also make it easier to resist Christmas cookies. And when a dangerous desire starts coming on, just remember: Gritting your teeth isn’t the best approach, as even the strongest mental muscles quickly get tired. Instead, find a way to look at something else.

—Jonah Lehrer is the author of “How We Decide” and “Proust Was a Neuroscientist.”

 

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