‘Pain as reward’ raises tolerance threshold

By Joanna Lyford, Senior medwireNews Reporter

An individual's ability to tolerate pain is influenced by their preconceptions and beliefs about the meaning of the pain, Italian researchers have shown.

They found that patients with a "positive approach" to pain had increased tolerance, an effect that was mediated by the opioid and cannabinoid systems.

"Therefore, the behavioral and/or pharmacological manipulation of the meaning of pain can represent an effective approach to pain management," write Fabrizio Benedetti (Università di Torino, Italy) in Pain.

For their study, Benedetti et al recruited 45 healthy men and women and submitted them to four sessions of experimentally induced ischemic arm pain. Before the pain task the participants were randomly assigned to one of three groups: positive, negative, or control.

The "negative" group was told that the purpose of the task was to study the "aversive emotional component" of pain, whereas the "positive" group was told that ischemia is beneficial to the muscles and that the greater the pain the greater the benefit. A control group received no pretask instruction.

All participants were told to tolerate the pain for as long as possible; pain typically became unbearable after about 14 minutes.

Results showed that pain tolerance in the control and negative groups remained stable over the four sessions of experimental pain. By contrast, pain tolerance in the positive group increased over the four sessions. Furthermore, the "positive" group had greater pain tolerance than the "negative" group at each of the sessions.

To investigate the underlying mechanisms, the pain tasks were repeated after administration of naltrexone, an opioid antagonist, and/or rimonabant, a CB1 cannabinoid receptor antagonist.

Neither of these drugs influenced pain thresholds in the negative group, whereas both drugs completely abolished the increased pain tolerance in the positive group. When the drugs were given together, the antagonism was greater than that produced by either drug individually.

"Pain can be better tolerated if its experience is somehow rewarding and this change in meaning involves at least two anti-nociceptive systems," conclude Benedetti and colleagues, who believe that their findings have important clinical and social implications.

They write: "First, it can explain several clinical observations, like the difference in pain perception in cancer pain, which frequently means death, and in postoperative pain, which is usually associated to healing and recovery. Second, the behavioral and/or pharmacological manipulation of the meaning of pain may represent an important tool in pain management. Third, the different meanings of suffering, either positive or negative, across different societies and religions may involve these mechanisms."

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