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Monday 17th June 2019

Placebo effect happens unconsciously

18th September 2012

Researchers in the United States say that the "placebo effect," in which a patient's condition improves even when the treatment they receive contains no active ingredients, works unconsciously.


The study set out to show why placebos and nocebos often affect clinical outcomes in patients, and concluded that the effects happen via a process that is not subject to our day-to-day awareness and over which we have no control.

According to previous research, a placebo effect--clinical improvement in the absence of any real treatment--can be experienced even without pills or other "medications," in any therapeutic situation.

The same is true of the nocebo effect, which has a negative effect on a patient which cannot be traced to material causes. Scientists had previously assumed that the effects were a result of conscious thoughts and beliefs.

Now, researchers writing in the Proceedings of the National Academy of Sciences (PNASO) say that the placebo effect has nothing to do with human cognition; rather it relies on a part of the brain that is separate from our cognitive awareness.

According to study first author Karin Jensen, of the Department of Psychiatry and the Martinos Center for Biomedical Imaging at Massachusetts General Hospital, a patient's conscious expectation of the direction their disease will take has little to do with a placebo effect.

Jensen, who is also on the Program in Placebo Studies (PiPS) at Beth Israel Deaconess Medical Center/Harvard Medical School explains in the report that humans can have certain expectations "automatically," without the need for thought.

Previously, scientists have believed that placebo responses were the result of a conscious expectation on the part of patients that their condition will worsen or improve.

But Jensen and her team said that certain brain structures, including the amygdala and the striatum, can process situations without thought, meaning that they can effect behaviour and cognition without ever coming to awareness.

The researchers carried out two experiments on 40 voluntary participants, who showed a placebo effect when heat was applied to their arm in line with expectations created by photos of human facial expressions, meaning that they experienced less pain when a face seemed less affected by pain. They also showed a "nocebo" effect, meaning that they experienced more pain when shown photos of people apparently in greater pain.

However, all participants had been given exactly the same heat stimulus throughout. Next, the study subjects were shown the same faces during heat stimulation, but too fast for them to register them consciously. The placebo and nocebo effects held true, even when the participants had no idea which faces they had seen.

According to senior author Jian Kong, from the same institutions, such a mechanism would generally be expected to be more automatic and fundamental to our behaviour than deliberate judgments and expectations.

The study authors said that it is the expectations of these unconscious processes that predict outcomes, rather than what a patient consciously believes will be the outcome of their treatment.

These instantaneous evaluations are formed in a split second in older parts of the brain, without any influence from the patient's expectations or intentions.


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