[Surfside] Scientists reveal the secret of cuddles

[Paul Makepeace]

http://www.newscientist.com/news/news.jsp?id=ns99992598

Scientists reveal the secret of cuddles

19:00 28 July 02   NewScientist.com news service  

Scientists have discovered why being cuddled feels so good - human skin
has a special network of nerves that stimulate a pleasurable response
to stroking.

The revelation came after doctors realised that a woman with no sense of
touch still felt a "pleasant" sensation when her skin was caressed.

Normal touch is transmitted to the brain through a network of
fast-conducting nerves, called myelinated fibres, which carry signals
at 60 metres per second. But there is a second slow-conducting nerve
network of unmyelinated fibres, called C-tactile (CT), the role of
which was unknown. The CT network carries signals at just one metre
per second.

"It must be used for unconscious aspects of touch because it is so
slow," says Ha*kan Olausson, who led the study at the Department of
Clinical Neurophysiology at Sahlgrenska University Hospital, Sweden. "It
seems the CT network conveys emotions, or a sense of self."

"This study definitely helps our understanding of how touch systems
work," says Brian Fiske, assistant editor at Nature Neuroscience. "The
researchers were very fortunate to have found a patient who had lost the
main touch receptors but still had the slow CT fibres."


Below the nose

Scientists have known for some time that myelinated nerve fibres
transmit information about touch, such as its strength and position. But
the function of CT fibres was a mystery. This was because it is
impossible to distinguish the CT fibre signals from those of the
continuously activated fast myelinated fibre.

The patient examined by the Swedish researchers had a disorder that left
her with no myelinated touch fibres in her body below the level of her
nose. But her CT fibres remained intact.

Olausson stroked the patient's arm and hand with a paintbrush. Although
she could not feel touch, tickle or vibration, the patient said she
experienced a "pleasant" pressure when her arm was caressed with a
paintbrush.

MRI scans of her brain revealed that the stroking activated insular
region of the cerebral cortex associated with emotional response.


Hairy skin

The researchers concluded that the CT system may be of important for
emotional, hormonal and behavioural responses to tactile stimulation.

"They are the opposite to pain fibres and give the message that the
touch is non- harmful," Olausson told New Scientist. "Stimulation of CT
fibres is probably linked to the release of pleasure hormones, like
oxytocin. Studies have shown that if you stroke infants, their levels of
oxytocin increase."

Further research by the Swedish team suggests that CT fibres are only
present in hairy skin - the patient showed no response to the palm of
her hand being stroked.

Olausson speculates that because the hand is used for so many critical
tasks, it needs to be very sensitive to touch and therefore has a
greater density of faster- conducting nerves.

Journal reference: Nature Neuroscience (DOI: 10.1038/nn896)


Gaia Vince


--
Paul Makepeace ....................................... http://paulm.com/

"If I'ld be me, myself, and I, then stones would sing and pebbles would
 dance."
   -- http://paulm.com/toys/surrealism/