By stimulating the brain’s feel-good reward centres in mice, researchers found they could boost the animals’ immune systems. The findings might explain the power of the placebo effect.

… though it should be noted ‘mind over body’ works only to a certain degree. There is little evidence that suggests placebos work well against chronic illnesses like heart disease, respiratory disease or cancer. Credit: Theworldcounts.com

The power of the placebo effect

In medical research, scientists often use placebos — an inactive treatment or substance, such as a sugar pill or sham procedure — to act as a control to gauge the supposed beneficial effects of the ‘real deal’, like a drug that actually contains an active compound.

These are employed because patients given the placebo think they’re receiving a standard care, a belief which causes many to experience the ‘placebo effect’ — an improvement in symptoms despite having received no active treatment.

The placebo effect is so remarkable that sometimes it seems to work just as well as standard care. Placebos have been found to be particularly effective against depression and stomach complaints, having the same effect as antidepressants in about a third of cases. In Germany, half of all doctors prescribe placebos for various ailments because these seem to work. This is despite doctors admit they don’t know how or why it works — they just know that patients feel better.

Placebo research found the more expensive the placebo treatment, the higher its chances of improving symptoms. Also, intravenous injections are shown to be more effective than oral medication, perhaps because it looks and feels a lot more like a “standard care”.

Ted Kaptchuk, a professor of medicine at Harvard Medical School and the director of placebo studies at Beth Israel Deaconness Medical Center, whose research has found placebo effects rival the effects of active medication in patients with asthma, told NPR:

“We have expectations; we have previous experience; we have non-conscious awareness. And we’re in a medical environment, and we’re used to that environment producing beneficial results. The ritual of medicine activates particular areas in the brain that actually will reduce pain, or at least reduce the sensations that we have in relation to pain.”

Brain over brawn

Immune cells taken from rodents who had their brains’ reward centres activated (right) killed more bacterial cells than those immune cells harvested from control mice (left). Credit: Nature Medicine

The exact mechanism by which a placebo treatment works to align the body with the mind’s healing intentions is where it gets blurry, though some research gives some hints. One study found patients who take placebos and think these will truly make them better release more natural painkillers, known as endorphins, in their brains. Another study found some people are more susceptible to the place effects due to varying levels of dopamine activity in the area of the brain known as the nucleus accumbens, a region involved with the ability to experience pleasure and reward.

Researchers at the Technion-Israel Institute of Technology’s Faculty of Medicine also singled out the nucleus accumbens as a likely source for the placebo effect.

“Our findings indicate that activation of areas of the brain associated with positive expectations can affect how the body copes with diseases,” said senior author Asya Rolls, an assistant professor at the Technion-Israel Institute of Technology’s Faculty of Medicine.

Rolls and colleagues incubated immune cells from mice exposed to E. coli bacteria. These cells came from mice which were either left alone or had their brains’ reward centre stimulated. These cells were twice as effective at killing the bacterial cells than the unstimulated ones, as reported in Nature Medicine.

In a second experiment, rodents were vaccinated with immune cells from mice who had their reward centre stimulated. These mice were also twice as likely to successfuly fight the infection. Certain immune cells also seemed to be more excited. Monocytes and macrophages were more efficient E. coli killers after nerve cell activation in the reward centre of the brain, specifically in the ventral tegmental area — a region heavily regulated by the mood-modifying chemical dopamine.

This area of brain ‘lights up’ during brain scanning of both rodents and humans when, for instance, a tasty meal or the prospect of sex is apparent.

“Feeding and sex expose one to bacteria,” explained Rolls said.

“It would give one an evolutionary advantage if—when the reward system is activated—immunity is also boosted.”

Ironically, this information might one day lead to an active drug made from molecules which interact with brain pathways in a way that might trigger this cause-and-effect. Essentially, an active drug that mimics placebo effects, but is not dependent on the patient’s mood or susceptibility to the placebo effect.