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Fur Science: Why Humans Love to Pet

Furry and hairy animals have specialized neurons that fire when petted or stroked, a study finds.

Hairy or furry skin is hard-wired for petting and stroking sensations, creating intense pleasure when touched this way, a study finds.

The research, published in the latest issue of the journal Nature, helps to explain why pets love to be petted, and possibly why human body pleasure zones tend to be where multiple hair follicles exist.

The ultimate euphoria center, though, is in the brain.

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"Scientists care about what feels good to animals, not just about things that feel bad, like painful stimuli," co-author David Anderson told Discovery News. "Both are important for understanding how the brain interprets the world around us and guides our behavior."

Anderson directs the David Anderson Research Group at the California Institute of Technology. He and his colleagues focused their analysis on mice, which often serve as models for other mammals.

The scientists used high tech imaging to monitor how neurons were activated when the mice were touched in various innocuous ways. A custom-designed brush and other methods were used to poke, pinch and stroke the mice.

These experiments revealed a previously undiscovered population of sensory neurons that ""innervate hair follicles," Anderson said. These neurons appear to be solely dedicated to massage-like stroking sensations. They were not activated during the other forms of touch.

"The neurons that detect stroking are probably wired into higher brain circuits that produce a reward or pleasure," he continued.

The researchers suspect similar sensory neurons with comparable properties exist in humans and most furry mammals. Since the sensation is connected to hair follicles, animals with many of them – such as cats and dogs – likely feel waves of pleasure when being petted. They certainly look like they do, as many pet owners could attest.

In terms of research directly on humans, a prior study found that hairy arm skin responds to gentle stroking more so than areas of skin with fewer hair follicles.

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"We don't know if the striking sensation would be lost if hair/fur fell out," Anderson said. Since the neurons are connected to follicles, it is possible that hair and fur are not necessary. A bald person, for example, can enjoy a head massage just as much as someone who has a full head of hair.

It is not clear why furry and hairy mammals possess the specialized neurons, but the scientists suspect that they evolved to promote the social and physical benefits tied to personal grooming and the grooming of others.

In humans, they might also help to explain the purpose and location of pubic hair. This hair could additionally promote warmth and protection, as well as facilitate the release of pheromones to attract mates.

Ardem Patapoutian of the Scripps Research Institute is a leading expert in sensory neuron function. He said that he agrees with the new paper's conclusions.

"Also," Patapoutian added, "I do believe that humans might also have similar specialized neurons."

He and Dr. Anderson, however, say that further studies are needed before that theory is fully confirmed.

Dec. 21, 2012

-- This year, a study published in the journal PLoS found that looking at cute animal photos helps people to improve their concentration. With that in mind, we present some of the cutest baby animal photographs of 2012. Taking a break to look at such photos may provide a beneficial boost. "For future applications, cute objects may be used as an emotion elicitor to induce careful behavioral tendencies in specific situations, such as driving and office work," wrote Hiroshi Nittono of Hiroshima University and his colleagues. Some of our favorite cute critter photographs this year came from the Chengdu Panda Base, which experienced a giant panda baby boom in 2012. Alejandro Grau, a spokesperson for the reserve, told Discovery News in November that "all the cubs are in good health and were photographed together for the first time."

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When this little female orange-headed Francois's langur was born at the San Francisco Zoo, the SF Giants baseball team went on a winning streak. "Things have turned literally since she's been born" Abigail Tuller, a spokesperson for the zoo, said in October. "She seems to have her strongest powers when the Giants are behind." That winning streak never ended. The Giants wound up winning the World Series pennant.

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Two-month-old Charlees, the rhino, spent an entire sunny morning happily running around her spacious digs at the San Diego Zoo Safari Park. Charlees is the 61st greater one-horned rhino born at the Safari Park since 1975, making the Park the foremost breeding facility in the world for this species. Once widespread in Southeast Asia, the greater one-horned rhinoceros now numbers approximately 2,800 and is listed as an endangered species by the International Union for Conservation of Nature.

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This clouded leopard cub and his brother were born this year in Nashville, Tenn., but traveled to the San Diego Zoo, which they now call home. The brothers, Riki-san and Haui-san, provide hope that breeding programs can successfully increase numbers of their critically endangered species.

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During spring 2012, Smithsonian's National Zoo welcomed the birth of this young black howler monkey. In the wild, threats to these monkeys include human predation, habitat destruction and being captured for captivity as pets -- since they are so cute.

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In April, a duckling whose mother was mauled to death by a fox was adopted by a Labrador retriever. Jeremy Goldsmith, owner of Fred the lab, said, "It is amazing to see the two of them together. When we found Dennis (the name he gave the duck) he was quite frail, and he clearly would not have survived another day on his own." He continued, "Fred, who has always been extremely loving, went straight up to him and began to lick the little bird clean. Since then, Dennis has not stopped following him around, and Fred has pretty much adopted him."

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Even killer whales have their cute moments, as this photo of a mother and son together proves. This year, we learned that the prolonged life spans of killer whale moms and human mothers is due, in part, to caring for offspring -- especially sons. "For most animal species, the potential for an individual to increase the propagation of its genes stops when they stop reproducing," Darren Croft, a senior lecturer in animal behavior at the University of Exeter, told Discovery News. "Our results show that, as with humans, female killer whales can continue to increase the propagation of their genes long after menopause." He added, "They do this by helping to increase the survival of their older sons, which in turn increases the number of grandchildren fathered by their sons. Through this process, evolution favors females that live longer after their menopause."

Yet another mother and baby, this time orangutans, were captured in a photo this year. As for killer whales (also known as orcas), orangutan mothers dote over their offspring.

In May, a fishing cat mother gave birth to a pair of kittens. Fishing cats in the wild are endangered and are native to South and Southeast Asia. The cats live near water, such as freshwater marshes and rivers.

This baby dama gazelle, which entered the world in 2012, has evolved for life in the desert. As adults, dama gazelles grow incredibly long legs and can run very fast. They also sport thick horns. Their diet includes grasses, leaves, shoots and fruits.

This young Savannah sparrow, snapped in 2012, has a short tail and a tiny head. It is a common songbird in North America, where it can be heard in farm fields and grasslands tweeting a loud, insect-sounding song.

While snakes seem to have faces that only a mother could love, this baby tentacled snake was a hit at Smithsonian’s National Zoo. Aside from their diminutive size and slithery cuteness, the snakes charmed zookeepers because the keepers had spent four years trying to breed this rare species. Tentacled snakes are native to Southeast Asian lakes and rice paddies.

In November, a study in the journal PLoS ONE reported that grey seal moms often exhibit a flexible parenting style. Sean Twiss of Durham University, who worked on the study, said, "In either resting or disturbed situations, seal mums behaved in very individual ways, some showing high levels of maternal attentiveness, others showing low levels." Surely this mother, caught playing with her pup, falls into the doting mom category.

A plethora of great giant panda pics came our way in 2012. We already have shown you one, but could not resist yet another. Here, giant panda cub Xiao Liwu (meaning "Little Gift") stretches out and shows his belly while animal care staff check him over during an exam at the San Diego Zoo.

Baby animals likely have been cute since the beginning of critter time on this planet. Cuteness makes them more appealing to adults, helping to ensure their care. We cannot show you a photo of a baby dinosaur, but we can show you this handprint of the baby dinosaur Massospondylus rom a nesting site in South Africa. This handprint reveals that the hatchlings walked on all fours, whereas adult dinos were known to walk on two legs. Our guess is that baby Massospondylus was extremely cute, at least by Jurassic standards.

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