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ScienceDaily (Aug. 21, 2009) reports on a discovery by scientists at UCLA that identifies a gene linked with physical pain sensitivity that is also linked with social pain sensitivity. The gene involves mu-opioids the most potent painkillers in or bodies.

Physical pain is not easy to define although at first it seems obvious:

But how is physical pain to be defined? For the purposes of research and diagnosis, pain

exists on two dimensions. The physical, sensory aspect of pain can be graded on intensity. However, it is the emotional, affective dimension, the from any other sensation (Sternberg, 2007). The combination of these two qualities—intensity and unpleasantness—leads to the unique sensation of pain, in all degrees and forms. Cortical representation of pain unpleasantness and intensity depends on overlapping, often co-activated, yet distinct brain areas (Price, 2000; MacDonald & Leary, 2005; Singer et al., 2004). The experience of pain can be broken down into four stages, as the center of pain-processing activity moves in from the periphery to central neural structures.

The UCLA research shows that changes in a gene named the mu-opioid receptor (OPRM1), previously known to be coonected with physical pain, is also connected to the amount of social pain a person feels in response to social rejection. This gene is rare and not the common form. People with this rare gene are more sensitive to rejection. Examination of data from their brains also shows more evidence of distress in response to rejection than those with the more common form.

Published on August 14th in the online edition of Proceedings of the National Academy of Sciences:

"…. the findings give weight to the common notion that rejection "hurts" by showing that a gene regulating the body’s most potent painkillers — mu-opioids — is involved in socially painful experiences too, said study co-author Naomi Eisenberger, UCLA assistant professor of psychology and director of UCLA’s Social and Affective Neuroscience Laboratory."

The type of OPRM1 gene in a subject was determined from their saliva and then sensitivity to rejection was measured. First, participants completed a survey that measured their self-reported sensitivity to rejection. They were asked, for example, how much they agreed or disagreed with statements like "I am very sensitive to any signs that a person might not want to talk to me." Then a smaller group of the original group was given functional magnetic resonance imaging (fMRI) testing at UCLA’s Ahmanson–Lovelace Brain Mapping Center during a virtual ball-tossing game in which participants were ultimately socially excluded. Subjects were told that they would be connected over the Internet with two other players who were also in fMRI scanners and that they would all be playing the interactive ball-tossing game. In reality, however, participants were playing with a preset computer program, not other people.

Initially, participants were included in the activity but were then excluded when the two other "players" stopped throwing the ball to them.

"What we found is that individuals with the rare form of the OPRM1 gene, who were shown in previous work to be more sensitive to physical pain, also reported higher levels of rejection sensitivity and showed greater activity in social pain–related regions of the brain — the dorsal anterior cingulate cortex and anterior insula — in response to being excluded," Eisenberger said.

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