Previous research has suggested you do not need to give a placebo to get a placebo effect. Placebo effects can be potentially active in any therapeutic situation. In a new study, published in the Proceedings of the National Academy of Sciences (PNASO), it was found that placebo and nocebo effects depend on brain function that are separate from cognitive consciousness.
First author Karin Jensen, PhD, of the Department of Psychiatry and the Martinos Center for Biomedical Imaging at Massachusetts General Hospital (MGH) and the Program in Placebo Studies (PiPS) at Beth Israel Deaconess Medical Center/Harvard Medical School explains, "A person can have a placebo or nocebo response even if he or she is unaware of any suggestion of improvement or anticipation of getting worse."
It has always been believed that placebo responses were linked to conscious thought, for instance, when people have the expectation to get better they will, or in the case if nocebos, they will deteriorate because they expect to get worse.
More recently, scientists have learned humans expect threat or reward quickly and automatically without needing to form the idea in their head consciously. As the authors explain certain structures like the amygdala and striatum, can process stimuli before they reach conscious awareness and can bring about non-conscious effects on human behavior and cognition.
Jensen and her team wanted to test whether placebo and nocebo effects can be activated outside of a person's conscious awareness when there is no expectation of improving or declining.
They conducted two experiments using 40 volunteers. In the first, researchers gave heat stimulation to participants' arms and showed them pictures of human male faces at the same time. The first image was related to with low pain prompts, while the second was related to high pain prompts.
Afterwards, patients rated their experience on a pain scale of 1 to 100, 0 being no pain and 100 being the worst, without their knowledge that all heat stimulations carried the same heat intensity. As anticipated, pain ratings correlated with learned associations. Subjects reported a pain rating of 19 when seeing the low pain face, while 53 was the most commonly reported number on the pain scale while seeing the high pain face, exhibiting a nocebo effect.
In the second experiment, subjects were given the same levels of heat stimulation. The same photos were shown, but only flashing by quickly so patients could not recognize them. Then participants then rated their pain again, showing a placebo effect to the low pain face, at a mean rate of 25. In response to the high pain face, a mean rate of 44 was recorded, or a nocebo effect.
The study's senior author Jian Kong, MD, also of MGH and the PiPS, commented,
"Such a mechanism would generally be expected to be more automatic and fundamental to our behavior compared to deliberate judgments and expectations. Most important, this study provides a unique model that allows us to further investigate placebo and nocebo mechanisms by using tools such as neuroimaging."
The authors conclude that it is not what patients think will happen that predicts outcomes, it is what the non-conscious mind expects without conscious thought. This mechanism is automatic, strong and rapid not depending on assessment and intention.
Written by Kelly Fitzgerald