Placebos work even without the patient's knowledge

Placebos work even without the patient's knowledge

Placebo: sham treatments can also work unconsciously

Apparently, the body can be tricked on the subconscious level, as researchers at Harvard Medical School found. If patients are unaware of a placebo treatment, pain-relieving effects can still be observed. Researchers sent hidden signals that activated the organism.

Research has been debating the placebo effect for decades. Conventional medicine assumes that naturopathy is the most important, most remedies only work because the patient expects a healing or pain-relieving effect. US scientists from the "Harvard Medical School" and other research institutions have taken a closer look at the effects of placebo's. They investigated whether, for example, a verbalized assumption leads to an analgesic effect or whether other mechanisms play a role.

Unconscious acceptance or verbalized information
The common theories of the human placebo effect are based on the assumption that verbalized information, conscious perceptions or various stimuli of the classical conditioning activate the placebo effect. As a rule, the placebo effect works if a doctor has previously signaled that the administered agent helps.

A patient comes to the doctor and complains of abdominal pain. After an in-depth examination, the doctor cannot find any organic findings and diagnoses functional abdominal pain. The family doctor gives the patient a pill, which however does not contain any detectable active ingredient. Nevertheless, the doctor leaves the patient on the assumption that it is a preparation for abdominal pain. The patient experiences less or no pain after ingestion because he expects the tablet to help. However, more and more research indicates that “behavior can be triggered beforehand by stimuli outside of conscious awareness”.

Only a few knew nothing about the placebo
To confirm this assumption, researchers from the medical faculty at Harvard University looked closely at signals and stimuli in relation to expectations in the course of a research project. In the science magazine "Proceedings of the National Academy of Sciences", the authors write, "Some of the subjects did not know that they were only receiving an apparent treatment. Nevertheless, the placebo worked ”.

40 healthy young women and men (24 women, 16 men, mean age 23 years) participated in the study. At the beginning of the experiment, all participants learned to cognitively combine a specific facial expression on a screen with a painful heat stimulus. Another facial expression, on the other hand, was painless. Depending on which image was shown in the training run, a thermal probe, which was attached to the left forearm of the participants, hurt more or less. On a scale from 0 to 100, the test subjects were asked to note how severe the pain stimulus was on their arm.

The unconscious level controlled signal stimuli
In the second round of the study, the participants were shown the same different faces. However, the test subjects did not know that the heat irritation remained the same. In the first part of the experiment, the faces were faded in for 100 milliseconds each. With this time phase, the test subjects were able to recognize the different faces on the conscious level. In the second run, the researchers only showed the images for about 12 milliseconds each.

"None of the participants could consciously recognize or distinguish the faces," the research team explained. Nevertheless, the subjects rated the stimulus as painful whenever "the image that was cognitively linked in advance to the unpleasant pain was shown". Conversely, the portrait was noted as "pleasant when the face flared up, which was associated with a harmless heat stimulus". This happened "regardless of whether the study participants had consciously recognized the image or not."

New insights into the placebo effect
As a result, the results could open “a whole new door to understanding placebos and the rituals of medicine,” said study leader Ted Kaptchuk from Harvard Medical School. The newly discovered mechanism "works automatically, quickly and is independent of deliberate considerations and evaluations," summarizes Kaptchuk.

According to the scientists, the newly gained knowledge is valuable for doctors, patients and clinical studies. "Without being aware of this, the patient apparently also registers subtle messages that the doctor sends, for example," the authors write. This could also explain why even unspoken expectations on the part of the doctor regarding a drug or therapy can have a positive effect on the patient's effect. (sb)

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Author and source information

Video: What Is a Placebo? Q and A with Ted Kaptchuk (September 2020).