“Neurobiologically, placebo analgesia is in many cases opioid-dependent and relies on frontal cortical areas and their projections to downstream effectors in the brainstem (1, 2). One possible mechanism of placebo analgesia is thus that cortical areas recruit the opioidergic descending pain control system in the brainstem (3), which ultimately inhibits nociceptive processing in the dorsal horn of the spinal cord in a gate-control manner (4). Behavioral data support the idea that placebo analgesia can act at the level of the spinal cord (5), but there is no direct evidence that nociceptive responses in the spinal cord are reduced under placebo analgesia.”

Here’s what they tested:

“We combined high-resolution functional magnetic resonance imaging (fMRI) of the human cervical spinal cord with a robust placebo analgesia paradigm (6) (fig. S1) to test the hypothesis that spinal cord blood oxygen level–dependent (BOLD) responses related to painful heat stimulation are reduced under placebo analgesia.”

They used heat to induce pain sensation in the subject’s arm. They found the strongest spinal fMRI response where they expected it, near the back of the spine between two neck vertebrae. They tricked the subjects into thinking that they had a fake cream and a lidocaine cream, and subjects reported less pain on the “lidocaine” (placebo) side.

Here’s the results:

“Our data provide direct evidence that psychological
factors can influence nociceptive processing
at the earliest stage of the central nervous system,
namely the dorsal horn of the spinal cord. They also
reveal that one mechanism of placebo analgesia is
inhibition of spinal cord nociceptive processing,
possibly mediated by the descending pain control
system (3) in a gate-control manner (4). It is likely
that the decreased BOLD responses we observed
are caused by endogenous opioids because opioid
antagonists block placebo analgesia (1) and because
recent fMRI data from rat spinal cord
showed morphine depression of dorsal horn BOLD
responses (7).”

Here’s their caveat emptor (can you do italics in a response?):

“However, our study cannot reveal the exact mechanism of spinal inhibition [i.e., effects on primary afferents (presynaptic), interneurons, or projection neurons (postsynaptic)] and whether the observed effect is specific for nociception, because we did not measure responses to innocuous stimuli.”

And here is their conclusion:

“Nevertheless, the demonstration that modulatory influences on nociceptive spinal cord activity are measurable by fMRI in humans opens up new avenues for assessing the efficacy and possible site of action of new treatments for various forms of pain, including chronic pain.”

That gives a path to investigate one of the things I was talking about above, a way to reliably access the placebo effect, although only for pain control. The Cosmos writer wants to extend this to “understanding _the_ placebo effect,” but there’s no reason to think that spinal pain pathways are involved in coordinating and facilitating all of the other biological responses that change healing, etc. A friend of mine is researching something that may be related to this, the sympathetic and parasympathetic nervous systems, that also have a spinal portion, and affect heart rate, enzyme production from most internal organs, speed of response, etc. Placebo pain management is important (since we have known for a long time that pain perception is very person- and situation-dependent), but it isn’t “THE placebo effect” that Alissa Jenkins is selling it as.

I can send the article to anybody who is interested, along with the supplementary material. The article was a one-page “Brevia” from Science (Science. 2009 Oct 16;326(5951):404.), and the supplemental material is just 11 (mostly text) pages. The supplement describes the experiment in more detail, and shows that the investigator almost certainly was not blinded, because they talk about the techniques they used to deceive the subjects. Intentional deception changes the need for blinding, and part of what they are measuring is the ability of the investigator to deceive the person into thinking the cream is lidocaine.

“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.”

This article fails to mention the fairly critical point about whether this study was double-blinded. I’m gonna guess that this study doesn’t in fact show anything new neurologically, just ties it in to placebos, because I can remember asking this exact question in neuroscience class 3.5 years ago and having a detailed discussion with the professor about how pain signals are gated.

I might dig the study up to see whether it was double-blinded, but I’m working through another one right now about nonmaterialist neuroscience (a peer-reviewed paper!), that seems to be fairly bad science.

http://www.cosmosmagazine.com/news/3187/mechanism-placebo-effect-discovered

BubbaRich, I think your experience with Tai Chi is a great analogy – especially since my mom has also taken Tai Chi classes. She never bought into the woo aspects, but they helped her with her balance and strength, which are beginning to deteriorate now that she’s in her seventies. I wasn’t about to talk her out of it, once I realized that she didn’t get into the qi and the meridians, etc.

Of course, I would speak up for two reasons – first, if the placebo took the place of treatment that really works on a treatable condition; and second, if the placebo could actually cause harm, as ReedE points out. I put chiropractic into that second category.

I hope to extend into discussion of that second category in my next post, sometime in the next few weeks.

I’d thought the value of placebo went away once one saw the wizard behind the curtain, seeing it was just a sugar pill. That the effect persists to some extent is fascinating.

Regarding Bubba’s points, it’s an interesting question where one draws the line.

Where there are no practical alternatives for a patient (such as one who believes that only acupuncture will reduce her pain) we should at least press to make that placebo as safe as possible.