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Facial Expression

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Is your smile fake or genuine? Elena Conis unravels the myriad goings-on that bring about that enchanting facial expression .

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Mona Lisa’s smile is mysterious, the Cheshire Cat’s is devious, the Joker’s is mischievous and Buddha’s beatific.
Humans probably have been smiling for as long as they have been around. But despite the long history of smiles, scientists still haven’t figured out exactly how or why the brain tells the lips to curve, the nose to wrinkle, the eyes to twinkle and the cheeks to lift.

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Babies generally start smiling at about six to eight weeks. Throughout childhood, boys smile just about as much as girls. That changes soon after puberty. Grown women smile more than men, and they also smile wider. Smiling, studies suggest, makes people appear more attractive, kinder and, by some accounts,easier to remember.

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Smiles carry myriad meanings: joy, amusement, politeness, mockery, disdain, lechery and deceit, to name a few. But no matter the emotion, all smiles call on many muscles and nerves, starting with one called cranial nerve seven.

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Cranial nerve seven leaves the brain and heads for the face, and at the point where the jawbone meets the skull, it branches off. Some of its tributaries travel to the muscles of the forehead, some to the eyes, some to the nose and others to the cheeks, lips and chin. When cranial seven sends its message to the face, the face will smile.

All smiles share something else in common: an emotional foundation. But there’s subtlety here. Depending on what the emotion is, the brain sends different instructions to the face — such was the conclusion of a young, 19th century French doctor named Guillaume Duchenne.

In the 1840s, Duchenne went from hospital to hospital in Paris carrying a box-like contraption of his own making. Using the coil and electrodes in the box, he applied volts of electricity to the faces of his patients. As their faces contorted, he took notes, ultimately creating a map of the face muscles and nerves.

In the process, Duchenne noticed that the range of human facial expressions includes two kinds of smiles: one that stops at the lips, and one that extends across the face, to the eyes. A smile engaging the eyes, he concluded, was a genuine smile, one that is technically called a  Duchenne smile.

A century after Duchenne, scientists studying facial expressions began applying electrical currents directly to the brain. They found that stimulating certain areas could induce a smile, and that stronger stimulation could make a person laugh.

But not all scientists got the same results. In one experiment, researchers at the University of California, Los Angeles, were examining the brain of a 16-year-old to find where her chronic seizures were originating. When they electrically stimulated an area on the left side of the girl’s brain, she grinned. When they increased the current, her smile turned to genuine laughter.

In another case, this one in Switzerland, researchers were looking for the source of seizures in a 21-year-old man. Stimulating an area on the right side of his brain caused him to smile, and increasing the current made him laugh. Unlike the 16-year-old girl, he insisted that he felt no joy.

The precise brain regions involved in smiling are still debated, but evidence from patients with brain damage has made one thing clear: The areas involved in instigating a polite, or voluntary, smile (the kind exchanged with a bank teller, for example) are not the same ones involved in genuine smiling (such as the kind that emerges on seeing a loved one or hearing a funny joke).

Some stroke victims, for example, can’t force a smile on demand, but will grin easily when truly happy  is  an indication that the stroke destroyed part of the brain controlling voluntary smiles. But sometimes the converse occurs: A stroke destroys the brain region controlling involuntary movement. In this case, the victim is no longer able to smile or laugh out of joy but can still force the corners of his mouth up into a polite smile.

Researchers are now tapping into another of the smile’s mysteries: They have evidence that a smile that’s a prelude to laughter may actually help the body heal. Preliminary studies suggest that genuine laughter can jolt the immune system into gear.

Source:The Telegraph (Kolkata,India)

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