"You can train your body into thinking it’s had medicine"

One of the most interesting articles I read recently: all you wanted to know about the placebo effect. What I learned:

  • The placebo effect works in reverse: if you think you are receiving a poison (when in fact you are not), you may actually die.
  • The placebo effect works also in animals.
  • The immunitary system associates harmless substances (i.e., sugar pills) with either drugs - in which case it triggers an immunitary response - or poisons - in which case it suppresses its normal immunitary response.

Here is the passage I found most fascinating:

In 1975, a psychologist in New York was studying taste aversion in a group of rats and got an utterly mystifying result.

Robert Ader, working at the University of Rochester, gave his animals saccharin solution to drink. Rats usually love the sweet taste but for this experiment, Ader paired the drink with injections of Cytoxan, which made them feel sick. When he later gave the animals the sweetened water on its own they refused to drink it, just as he expected. So to find out how long the learned aversion would last, he force-fed this harmless drink to them using an eyedropper. But the rats didn’t forget. Instead, one by one, they died.

Though Cytoxan is toxic, Ader’s rats hadn’t received anything close to a fatal dose. Instead, after a series of other experiments, Ader concluded that when the animals received saccharin and the drug together, they hadn’t just associated the sweet taste with feeling sick, they’d also learned the immunosuppression. Eventually, they’d responded to the sweetened water just as they had to the drug.


[...] a similar discovery had already been made in Russia. In the 1920s, researchers at the University of St Petersburg were following up on Pavlov’s work, to see which other physiological responses could be conditioned.

Among them was the immunologist Sergey Metalnikov. Instead of suppressing the immune system, like Ader would, Metalnikov wanted to boost it. In one series of experiments, he repeatedly warmed guinea pigs’ skin at the same time as giving them injections (small doses of bacteria, for example) that triggered an immune response. Then he gave them – and another group of guinea pigs that hadn’t had this conditioning – a normally lethal dose of Vibrio cholerae bacteria, at the same time as warming their skin. The unconditioned animals died within 8 hours, Metalnikov reported, whereas the conditioned ones survived an average of 36 hours, and some of them recovered completely. Their response to a learned cue – the feeling of heat – appeared to have saved their lives.