In a new study published recently in Nature Neuroscience, a group of researchers say they have discovered a new class of nerve fibers responsible for sending pleasure signals to the brain. They believe that the study could shed light on the role that physical contact plays in sustaining long-term emotional bonds between humans.
Researchers say that the patients’ skin had to be stimulated at a certain speed and in certain locations in order for these nerves to discharge their pleasure-inducing messages.
“There are some (biological) mechanisms in place that are associated with behavior and reward which are there to ensure relationships continue,” says professor Francis McGlone, one of the researchers involved in the project.
The majority of similar research in the field has traditionally focused on elucidating how nerve fibers transmit the sensation of pain to the brain. Dysfunction in the peripheral nervous system for example, a condition known as Neuropathy, can cause nerve cells to spontaneously discharge pain signals, creating the sensation of physical pain even in the absence of external stimuli.
Researchers involved with this study are seeking to understand neurological phenomenon from another angle.
The project was a cooperative effort between scientists from the University of Gothenburg in Sweden, the University of North Carolina and the Unilever company.
The study examined the neurological responses of twenty patients as their arms were lightly stroked at various speeds. They found that when the subjects identified a stimulus as pleasant, a class of neurological tissue known as “C-tactile” nerve fibers had been stimulated.
They also discovered that these fibers were only activated within a certain range of speeds ““ between 4-5 cm per second ““ and that slower and faster stimuli were not able to produce the same pleasurable sensation.
In addition, they observed that “C-tactile” nerve fibers were only located on hairy areas of the arm, and that similar stimulation of the hands did not have the same effect.
Professor McGlone of Unilever, who transitioned to the private sector after years of university research in the field of neurology, referred to this phenomenon as a sort of socio-biological “design”.
“We believe this could be Mother Nature’s way of ensuring that mixed messages are not sent to the brain when it is in use as a functional tool,” he said, adding that the speed at which arm-stroking is considered pleasurable corresponds to the same speed with which mothers caress their infants and couples express affection.
McGlone added that it is just another device that evolution has invented for supporting emotional bonds between individuals.
“Our primary impulse as humans is procreation,” adds Professor McGlone. “But there are some mechanisms in place that are associated with behavior and reward which are there to ensure relationships continue.”
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