British researchers at the University of Bristol say they've just finished creating a new set of mathematical models which are capable of explaining why the placebo effect occurs, and when.
In addition, the models can also predict when an instance of this effect will occur, the team reveals in a paper published in the August 30 issue of the scientific journal of Evolution and Human Behavior.
In the paper, entitled “Understanding the placebo effect from an evolutionary perspective,” researcher Dr. Pete Trimmer explains how the work of theoretical psychologist, professor Nicholas Humphrey, was used as a stepping stone for this study.
The placebo effect has been a mystery to the scientific community for a long time. It occurs, for example, when a patient is given a sugar pill, and is told that the drug is actually a medication that treats a disease they are suffering from.
The patient experiences the relief usually associated with that drug, even though they have no traces of the active chemical compounds in the body. One of the leading explanations is that placebo works based on patients' beliefs.
An age-old question related to the problem is why humans did not evolve a faster, more reliable self-healing mechanism over millions of years of evolution. The UB team created the models to examine the “trade-off between the costs and benefits of an immune response when faced with a health problem.”
The investigation was conducted by experts with the University of Bristol
School of Biological Sciences (SBS) Modeling Animal Decisions group. The main conclusion of their research is that the placebo effect is modulated by the patient’s expectations.
Some time ago, Humphrey proposed that holding back the immune system from becoming activated is sometimes positive for human health, because there is no clear way for our body's natural defenses to know the state of the world outside. Thousands of years ago, the risk of starvation was still very real.
As such, external clues evolved to the point where they could alter the immune system's response level.
“The placebo effect comes down to expectations about when to take action. Waiting for a useless pill before taking action is not optimal. But the general responsiveness to cues is adaptive, so it is logical for evolved organisms to display the placebo effect,” Trimmer explains.