Distracted by Placebos ...
Image CC Murtada al Mousawy: http://bit.ly/xbxTOF
By Gavin Hubbard, Feb 18th 2012
Its study can be traced back to World War II and the white lie of a nurse, working with the anaesthetist Henry Beecher, told to a severely injured soldier. With the morphine supplies having run out, and the soldier desperately needing surgery, the nurse assured the soldier that she was injecting him with a strong painkiller, but in reality it was nothing more than salt water (saline), yet, incredibly, it still relieved the soldier’s pain.
Pain and the placebo effect – where a sham drug or treatment somehow results in a perceived or actual effect – have long been study partners since that time. Beecher went on to publish one of the earliest papers on the subject of the placebo (‘The Powerful Placebo’) and continued to research it for much of his life. Now new research from Columbia University and the University of Colorado, published in Psychological Science, has used pain to help tease apart how our minds are involved in the weird world of the placebo.
How the placebo weaves its weird magic in our brains is still largely unknown, but it is thought to be through the mental processes involved in conditioning and expectation. However, identifying brain areas active under a placebo only lets us infer what processes – such as conscious thought or planning – might be involved, since many brain areas have multiple functions.
Its study can be traced back to World War II and the white lie of a nurse, working with the anaesthetist Henry Beecher, told to a severely injured soldier. With the morphine supplies having run out, and the soldier desperately needing surgery, the nurse assured the soldier that she was injecting him with a strong painkiller, but in reality it was nothing more than salt water (saline), yet, incredibly, it still relieved the soldier’s pain.
Pain and the placebo effect – where a sham drug or treatment somehow results in a perceived or actual effect – have long been study partners since that time. Beecher went on to publish one of the earliest papers on the subject of the placebo (‘The Powerful Placebo’) and continued to research it for much of his life. Now new research from Columbia University and the University of Colorado, published in Psychological Science, has used pain to help tease apart how our minds are involved in the weird world of the placebo.
How the placebo weaves its weird magic in our brains is still largely unknown, but it is thought to be through the mental processes involved in conditioning and expectation. However, identifying brain areas active under a placebo only lets us infer what processes – such as conscious thought or planning – might be involved, since many brain areas have multiple functions.
Credit Mark Lythgoe & Chloe Hutton, Wellcome Images CC: http://bit.ly/xMYaRH
Neuroimaging techniques, such as fMRI and PET scans, have identified an area responsible for conscious actions and processes (‘executive processes’) called the dorsolateral prefrontal cortex (DPC) when people are given a placebo. One recent study even showed that the level of pain relief from a placebo could be predicted based on the magnitude of activity in this area. Such evidence suggests the DPC might be one route through which expectations are transformed into placebo painkilling; that the effect is somehow governed by ‘executive processes’ such as attention and working memory.
Making high demands on attention and working memory has previously been shown to reduce pain too, in this case by using a difficult task to distract attention away the from the experience of pain. Knowing this, and that the DPC is appears to be involved in the placebo effect, the researchers decided to investigate if a task that competes for the psychological resources of attention and working memory would reduce the placebo effect, thereby determining if they were involved in it, or if some other process was responsible.
To do this the researchers used 33 volunteers across three sessions. The first session was used to calibrate volunteers’ pain reception against the same scale of 1 (no pain) to 100 (worst imaginable pain); the rating was used so that pain at standardised levels of 10 (low), 50 (moderate) and 90 (high) could be used for all participants.
(Personally, my favourite pain scale can be found here.)
Making high demands on attention and working memory has previously been shown to reduce pain too, in this case by using a difficult task to distract attention away the from the experience of pain. Knowing this, and that the DPC is appears to be involved in the placebo effect, the researchers decided to investigate if a task that competes for the psychological resources of attention and working memory would reduce the placebo effect, thereby determining if they were involved in it, or if some other process was responsible.
To do this the researchers used 33 volunteers across three sessions. The first session was used to calibrate volunteers’ pain reception against the same scale of 1 (no pain) to 100 (worst imaginable pain); the rating was used so that pain at standardised levels of 10 (low), 50 (moderate) and 90 (high) could be used for all participants.
(Personally, my favourite pain scale can be found here.)
Still from a good Youtube vid on the placebo effect (see below)
On the second and third days the volunteers completed two sessions, one placebo and one control. In both the placebo and control sessions the volunteers had a cream applied to their arms beforehand; for the placebo session they were told that it was a ‘powerful painkiller’ while for the control session they were told that the cream was just a normal cream with no painkilling effects. Each session (placebo and control) had two runs of five blocks in which they were asked to rate the level of pain felt.
In one run the volunteers were asked to perform a difficult memory task, called the 3-back test, which would call upon their working memory and attention. The test involves showing a series of letters on a screen, the volunteers have to say if the current letter is the same, or not, as the letter shown three letters before. In the second run, the volunteers were asked simply to stare at a cross on a screen. For both runs the blocks of pain were administered by the researchers and then rated by the volunteers.
The results showed that when either the placebo alone or the control plus 3-back task was given the volunteers reported less pain than when just staring at the cross on the screen with no placebo.
So, this didn’t add a huge amount to what was already known, placebos can cause a reduction in pain, and so can distraction. The interesting thing was what happened when they looked at the data for placebo plus the 3-back test.
Combining the 3-back test with the placebo was striking because the painkilling effect was almost exactly additive. Distraction and the placebo didn’t interact or interfere with each other, even though they potentially relied on the same processes of attention and memory. They also assessed the volunteers’ performance on the 3-back test with and without placebo, and found no difference in performance of this task with and without placebo, which would be expected if they relied upon the same mechanisms.
The researchers suggest that if placebo pain relief is due to attention and working memory it is unlikely to be due to it actively redirecting attention away from pain. They believe that that this is strong evidence that the processes of working memory and attention are not required for the placebo effect and that both placebo and distraction are two separate routes to pain relief.
You can find a copy of the paper on the researchers’ home page here: http://wagerlab.colorado.edu/files/papers/Buhle_Distraction-Placebo_Psych-Sci_In-press-final_2012.pdf
Also, take a look at the youtube vid below for an excellent 3 min summary of some of the weird things we now know about the placebo effect.
In one run the volunteers were asked to perform a difficult memory task, called the 3-back test, which would call upon their working memory and attention. The test involves showing a series of letters on a screen, the volunteers have to say if the current letter is the same, or not, as the letter shown three letters before. In the second run, the volunteers were asked simply to stare at a cross on a screen. For both runs the blocks of pain were administered by the researchers and then rated by the volunteers.
The results showed that when either the placebo alone or the control plus 3-back task was given the volunteers reported less pain than when just staring at the cross on the screen with no placebo.
So, this didn’t add a huge amount to what was already known, placebos can cause a reduction in pain, and so can distraction. The interesting thing was what happened when they looked at the data for placebo plus the 3-back test.
Combining the 3-back test with the placebo was striking because the painkilling effect was almost exactly additive. Distraction and the placebo didn’t interact or interfere with each other, even though they potentially relied on the same processes of attention and memory. They also assessed the volunteers’ performance on the 3-back test with and without placebo, and found no difference in performance of this task with and without placebo, which would be expected if they relied upon the same mechanisms.
The researchers suggest that if placebo pain relief is due to attention and working memory it is unlikely to be due to it actively redirecting attention away from pain. They believe that that this is strong evidence that the processes of working memory and attention are not required for the placebo effect and that both placebo and distraction are two separate routes to pain relief.
You can find a copy of the paper on the researchers’ home page here: http://wagerlab.colorado.edu/files/papers/Buhle_Distraction-Placebo_Psych-Sci_In-press-final_2012.pdf
Also, take a look at the youtube vid below for an excellent 3 min summary of some of the weird things we now know about the placebo effect.
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