For he first time, a physiological mechanism for the 'placebo effect' has been discovered by scientists.
Credit: Wikimedia
SYDNEY: A key to understanding the mysterious 'placebo effect' has been unlocked by scientists: placebos may work by blocking pain signals in the spinal cord from reaching the brain.
The placebo effect has long been a scientific mystery: it occurs when a patient's medical condition responds to treatment that is either fake or contains inactive substances. It was originally thought to be a psychological phenomenon related to the perception and expectation a patient has; if the inactive substance (or 'placebo') is viewed as helpful, it may heal, but if it is viewed as harmful, it can cause negative effects.
"We found that when people experience pain relief due to a placebo administration, they also show reduced neuronal activation to painful stimulation in their spinal cord," said research team member Falk Eippert, a neuroscientist with the University Medical Centre Hamburg-Eppendorf, Hamburg, Germany.
"This shows that psychological factors such as placebo can have a profound impact on pain processing."
Conditioning and expectation
Currently, the placebo effect is thought to depend mainly on two phenomena - conditioning and expectation. Conditioning is a process when, for example, we see a doctor several times who helps us to recover each occasion. Eventually we are conditioned to get better simply by going to the doctor - no longer is therapy required to make us recover.
Expectation is a more conscious process that depends on the context of a therapeutic situation. For example, if we are made to expect that a certain treatment will improve our health, we then might get better even if the actual treatment does nothing at all.
Both mechanisms work together and help to generate therapeutic benefits.
Placebos are typically used as 'controls' in experiments that test new treatments: patients are randomly given either the real drug or a placebo, and neither they nor the staff administering the trial know which patient has received the real treatment. Often, some of the patients given inactive substances also improve.
When a substantial number of people taking the placebo get better too, it makes it hard for researchers to determine whether a new drug is actually of any benefit. Placebos can be applied to a variety of illnesses, and when they have a pain-relieving effect (as in this study), this is called 'placebo analgesia'.
Deep in the brain
While there has long been an understanding that the 'placebo effect' is rooted deep in the brain, recent advances in imaging technology allowed the scientists to scan neuronal activity in the spinal cord. This part of the body acts as the entry station of the central nervous system for pain messages that come from the body.
This showed that psychological factors, such as placebo, can have a profound impact on pain processing, affecting not only cognitive areas deep in the brain, but down the spinal cord, where neuronal activity was inhibited.
Throughout the study, the researchers applied painful heat to the arms of 15 healthy men, and compared the spinal cord responses when they thought they had been treated with either an anaesthetic cream or a placebo.
Both creams, in fact, were inactive. But the fMRI scans (functional magnetic resonance imaging) showed nerve activity was reduced significantly when subjects believed they were getting the anaesthetic.
Natural endorphins
The scientists suggest this may be because when patients expect a treatment to be effective, the brain area responsible for pain control is activated, releasing natural endorphins that travel down the spinal cord to suppress incoming pain signals.
This means patients feel better regardless of if the treatment had any effect.
While Falk does not believe this study will have any immediate impact on patients suffering from pain disorders, he does suggest benefits to showing it is possible to measure controlled influences on spinal cord pain responses.
"It might help in the development of new treatments for pain, by allowing [scientists] to test the efficacy and possible site of action of new treatments," said Falk.
Better understanding of pain
Jon Jureidini, a psychiatrist with the University of Adelaide, Australia, agrees that this discovery expands our understanding of pain.
"This is very interesting for the scientific community interested in pain. While current patients may not benefit, it provides hope for patients down the line" he said.
Edzard Ernst, a physician with the University of Exeter, United Kingdom, and a specialist investigator of the validity of alternative remedies, was intrigued by the findings.
"This study provides a novel mechanism for explaining how a placebo might lower pain perception on the level of the nervous system. Of course, the findings require independent replication, but they are certainly thought provoking and exciting," he said.
