December 2002, Vol 23, No 12

R&D
News of science, medicine, and technology 

Wired for a Touch 
by Josie Glausiusz

A poke, a pat, a nudge, and a stroke may seem like similar forms of
touch, but the brain does not seem to perceive them the same way. Recent
studies of a patient with a unique disability show that the differences
may be hardwired into the body. One sensation—a soft caress—is processed
by a set of nerves totally separate from those that mediate all other
types of touch.
 
Neuroscientist Håkan Olausson of Sahlgrenska University Hospital in
Göteborg, Sweden, made this discovery while examining a patient whose
rare autoimmune disease left her with minimal bodily sensation below the
nose. Although she could still feel heat, cold, and pain, she had lost
her sense of touch and could no longer perceive the angle of her limbs.
Doctors discovered that the disease had destroyed the patient's
fast-conducting neurons, which had been thought to transmit all forms of
touch to the brain, leaving only the slow-conducting fibers, which
communicate pain and temperature. Yet when Olausson stroked the back of
the woman's hand with a soft paintbrush, she reported feeling a faint
and agreeable pressure. That unexpected response indicates that some of
the slow fibers were also signaling the caress.
 
Magnetic resonance imaging showed that these nerves stimulate the
insula, a deep-brain region that processes emotion. "The areas activated
in this patient are also activated if you look at someone that you're
deeply in love with," Olausson says. He theorizes that the caressing
nerves play a key role in sexual arousal, the release of hormones, and
even infant development. "Others have shown that if you caress newborns,
they get increased levels of oxytocin. This hormone makes the child
calmer, improves breast-feeding, and promotes growth," Olausson says.
"It emphasizes how important skin is as an emotional organ." 

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