Placebo effect in the context of Scientific control

In the design of experiments, hypotheses are applied to experimental units in a treatment group. In comparative experiments, members of a control group receive a standard treatment, a placebo, or no treatment at all. There may be more than one treatment group, more than one control group, or both.

A placebo control group can be used to support a double-blind study, in which some subjects are given an ineffective treatment (in medical studies typically a sugar pill) to minimize differences in the experiences of subjects in the different groups; this is done in a way that ensures no participant in the experiment (subject or experimenter) knows to which group each subject belongs. In such cases, a third, non-treatment control group can be used to measure the placebo effect directly, as the difference between the responses of placebo subjects and untreated subjects, perhaps paired by age group or other factors (such as being twins).

Psychic surgery is a medical fraud in which practitioners create the illusion of performing surgery with their bare hands and use sleight of hand, fake blood, and animal parts to convince the patient that diseased lesions have been removed and that the incision has spontaneously healed. The technique may fool the general public, but it can be observed by experienced stage magicians, who use the same sleight of hand techniques for entertainment.

The US Federal Trade Commission described psychic surgery as a "total hoax". It has also been described as fraud, fakery, deceitful, irrational, charlatanry, and quackery. Even supporters have been forced to admit that sleight-of-hand tricks were "widely used" and that charlatans were common and miracles unlikely. Psychic surgery may cause needless death by keeping the ill away from life-saving medical care. Medical professionals and skeptics classify it as sleight of hand and any positive results as a placebo effect.

Lourdes water is water which flows from a spring in the Grotto of Massabielle in the Sanctuary of Our Lady of Lourdes, France. According to Catholic tradition, the location of the spring was described to Bernadette Soubirous by an apparition of Our Lady of Lourdes on 25 February 1858. Since that time, many millions of pilgrims to Lourdes have followed the instruction of the Blessed Virgin Mary to "drink at the spring and bathe in it".

Since the supposed apparitions, many people have claimed to have been cured by drinking or bathing in it, and the Lourdes authorities provide it free of charge. Those claims have been described as an example of the placebo effect.

The nucleus accumbens (NAc or NAcc; also known as the accumbens nucleus, or formerly as the nucleus accumbens septi, Latin for 'nucleus adjacent to the septum') is a region in the basal forebrain rostral to the preoptic area of the hypothalamus. The nucleus accumbens and the olfactory tubercle collectively form the ventral striatum. The ventral striatum and dorsal striatum collectively form the striatum, which is the main component of the basal ganglia. The dopaminergic neurons of the mesolimbic pathway project onto the GABAergic medium spiny neurons of the nucleus accumbens and olfactory tubercle. Each cerebral hemisphere has its own nucleus accumbens, which can be divided into two structures: the nucleus accumbens core and the nucleus accumbens shell. These substructures have different morphology and functions.

Different NAcc subregions (core vs shell) and neuron subpopulations within each region (D1-type vs D2-type medium spiny neurons) are responsible for different cognitive functions. As a whole, the nucleus accumbens has a significant role in the cognitive processing of motivation, aversion, reward (i.e., incentive salience, pleasure, and positive reinforcement), and reinforcement learning (e.g., Pavlovian-instrumental transfer); hence, it has a significant role in addiction. In addition, part of the nucleus accumbens core is centrally involved in the induction of slow-wave sleep. The nucleus accumbens plays a lesser role in processing fear (a form of aversion), impulsivity, and the placebo effect. It is involved in the encoding of new motor programs as well.

Placebo-controlled studies are a way of testing a medical therapy in which, in addition to a group of subjects that receives the treatment to be evaluated, a separate control group receives a sham "placebo" treatment which is specifically designed to have no real effect. Placebos are most commonly used in blinded trials, where subjects do not know whether they are receiving real or placebo treatment. Often, there is also a further "natural history" group that does not receive any treatment at all.

The purpose of the placebo group is to account for the placebo effect, that is, effects from treatment that do not depend on the treatment itself. Such factors include knowing one is receiving a treatment, attention from health care professionals, and the expectations of a treatment's effectiveness by those running the research study. Without a placebo group to compare against, it is not possible to know whether the treatment itself had any effect.