11 March 2004

Cognitive factors in the placebo effect

More interesting stuff on the placebo effect in pain reduction.

From: SCIENCE VOL 303 20 FEBRUARY 2004 (p.1121)

In this study, headed by Tor Wager of the University of Michigan, Ann Arbor, subjects were given an inert salve that they were told was being tested as an analgesic cream. They were then given a shock or painful heat stimulus on the wrist. Those who showed increased activity in the prefrontal cortex prior to the stimulus also showed the biggest reduction of activity in pain-sensitive brain regions and reported the greatest pain reduction—suggesting that anticipation of pain relief is intimately tied with actual pain reduction. Co-author Richard Davidson of the University of Wisconsin, Madison, says this indicates that cognitive control may be crucial for downregulating pain circuitry. Presumably, he says, more prefrontal activity reflects “the active maintenance of a [mind]set” associated with pain relief. Mayberg, who has done brain-imaging studies on placebo effects with depressed patients, says the study supports the notion that it may be possible to predict response to medication by looking at the “expectation component” in patients’ brain scans.

To my mind, the stuff about the placebo effect is some of the most philosophically suggestive material in the pain science literature. I mean, (and this is from other studies) how can you not be curious about the fact that the analgesic effect of a placebo is almost always 50% of the actual analgesic effect of the drug the patient thinks she's getting (that is, if you tell her its asprin, her pain will be reduced 50% of what it would be with actual asprin; same thing with morphine). Of course, the phenomenon is extremely complicated: injected placebos are more effective (overall) than ingested ones which are in turn more effective than topical salves.