The objective of a placebo is to compare and assure that a new drug or operational procedure is effective. In experiments, the placebo is an inactive substance or procedure used as a control in an experiment (1). The placebo looks, tastes or feels just like the actual treatment (2). A false procedure for example, may consist of advising a person that he/she will be operated on and then making an incision into a person without operating. Subjects are advised of their probability of receiving actual treatment in order to maintain the expectation level of the participants. The efficacy of making an incision maintains the expectation level of the subject because the presence of a scar raises their belief that they were placed in the actual treatment group. Whether the placebo is a 'sugar pill' or an incision, the purpose of providing a false 'treatment' is to control for the amount of variance subjects already have within a given experiment.
By controlling for subject expectation, experimenters are trying to eliminate the placebo effect. The placebo effect occurs when the placebo, which can not on its own merit have any affect, does in fact have the same or similar affect as the experimental substance or procedure (1). However, some double-blind control studies use active placebos. Active placebos contain compounds which warrant side effects so that the subject feels as though they are receiving therapeutic treatment. The efficacy of the placebo in experiments, commonly account from 30-40% and sometimes up to 75% or 80% (2).
In the early 18th century, the word placebo was associated with quackery (3). Although the reason for the high success rate of the placebo is yet to be explained, experimenters have hypothesized plausible explanations for its effect. Advanced models attempting to explain placebo effects emphasize the role of expectations, anxiety and learning (3).
The placebo effect illustrates the effectiveness of the physician's role in 'healing' a patient. Past research show that a patient's high opinion of the physician prescribing the treatment (4) as well as the doctor's personality can invoke the placebo effect. Furthermore, research has shown that an amiable doctor with a positive outlook of a drug treatment would induce the placebo effect.
The power of the placebo is more readily explained as a function of the individual because the placebo effect can rely on the amount of faith an individual has for a given treatment. One suggestion is that placebo effects may be due to anxiety reduction. Stress and anxiety adversely affect the body and increase an individual's focus on symptoms (4). A decrease in the body's stress and anxiety level by a well-known doctor alleviates the patient's worry and pain leading to a 'curing' of the symptoms. It has been shown that placebos may be more effective among highly anxious people because the adverse effects interact with the physiological processing (3). There is evidence that there might be an alteration in the body's endogenous opioid release. Pain relief in patients provided via placebo, may be caused by a release of endorphins in the brain. Endorphins are the body's own morphine-like painkillers (2). Within the nervous system, there are specific pathways that modulate pain when stimulated by these endorphins. As a patient anticipates symptom relief, the expectation of receiving an active substance, alone, may be activating the pain pathway thereby reducing symptoms. The presence of a substance probably activates the pain-inhibition because unaware of the treatment group, the patient is led to believe that they have received an active substance.
Another pathway probably activated in conjunction with the endorphins is the brain's reward pathway which extends from the forebrain to the midbrain and into the hindbrain. The reward pathway is comprised of an array of complex structures but stimulation of specific nerve fibers, which pass through the hypothalamus, can increase behavioral output (5). For example, experiments have demonstrated that an electrode stimulating the medial forebrain bundle of a rat provided the highest rate of pressing responses by the rat (5). The increase in behavioral output suggested that self-stimulation of this region was rewarding. Furthermore, stimulation of the medial forebrain bundle in a rhesus monkey elicited self-starvation; the monkey stopped eating in order to obtain rewarding brain stimulation (5).
The cortex of a rhesus monkey is more sophisticated than a rat and has a closer resemblance to the human cortex. Observing the compulsive behavior influenced by stimulation to the reward system in rhesus monkeys demonstrates that maybe humans can activate the catecholamines like, dopamine, to trigger a particular behavior. It is suggested that placebo subjects can trigger this pathway because patients unaware that they were given a placebo are experiencing a type of gratification or reward. The personal gratification can activate the release of dopamine into the system leading to an altered mood state. Drugs that manipulate the catecholamine system have a powerful effect on mood...[and] agents which elevate catecholamines or mimic the action of catecholamine facilitate self-stimulation (5). In light of the rewarding effects depicted in rats and rhesus monkeys it seems plausible that in humans, a placebo, which has no inert effects, is somehow influencing the levels of neurotransmitters in the body.
The mechanisms involved in experiencing symptom relief can be understood by the activation of the reward and endorphin pathways. However, this accounts for biological aspect of the placebo effect but what triggers these symptoms? Commentaries on the efficacy of the placebo make reference to the attitudes or beliefs of the individuals and how these items of consciousness play a role. However, what is meant by a conscious experience? Is consciousness a state of awareness for tactile modalities? The first relating form of consciousness is the concept of self-awareness (6). Consciousness is similar to the I-function in how the body and mind interconnect to facilitate a sense of experience. Using an analogy of a box, the nervous system is constantly receiving numerous inputs and releasing output. However, there is another portion of this nervous system which characterizes the I-function; the part that contributes in the body's central pattern generators to aid in our interaction with the periphery, experience and receiving reward.
The inhibition of activity, which can be applied to the I-function, suggests that it is located in the neocortex. Bilateral damage to the Intra-Laminar Nuclei (ILN), the divider of the two thalami, appears to abolish the state of waking consciousness (7). It is not being assumed that the ILN is the source of consciousness but it refers to the idea that the I-function, which works with the nervous system, can be 'disconnected' from the body with damage to the neocortex. The 'disembodiment' of the conscious from the nervous system demonstrates a loss of experience or self-awareness. The concept of self-awareness is an important factor because it facilitates the power of the placebo.
Double-blind controlled experiments are unable to control for the sense of experience and self-awareness of the subject that makes the study vulnerable to the placebo effect. Subjects used in drug studies are at the stage in life where they are 'aware' that new drugs are being developed to combat symptoms. For example, in one study subjects were given measured doses of alcohol but the control group was given a non-alcoholic beverage which they believed to be alcohol (1). Needless to say, some of the placebo-drinking group behaved as though they were given alcohol. For these subjects the suggestion of drinking alcohol produced the inebriated behavior (1). It is this conscious knowing and expectation stemming from the I-function that activates the endogenous systems of the nervous system which produces the phenomenal placebo effect. Also, this study illustrated the strength of suggestion and the effects of expectation on behavior. What if the confounds of awareness and/or expectations could be removed from experiments but have an intact I-function? Would the placebo still turn out better than the treatment?
To test this, subjects would need to be young but capable of obeying simple commands like, 'Open your eyes'. The age of 4 is good because it is necessary to have subjects at a stage in life where they are conscious and capable of comprehending simple instructions but have yet to experience enough life to have developed expectations and 'awareness' about treatments and the extraneous variables (for example, physician influence) involved in the placebo effect. The patients' mind somehow influences other physiologic systems in the body which bring about positive results (2). As a young child, the I-function is a more active participant in the involvement of the body with the world than with suggestions or expectations. The I-function's primary concern of the body and world makes the child considerably obsolete from the influential power of the mind.
In the end, the placebo effect is a struggle in maintaining a co-habitative environment for the mind's prior experiences and the body's desire to reach beyond its present state. It also illustrates the considerable healing power of the mind (4). The I-function and consciousness are, indisputably, unexplainable phenomena which makes it difficult to reveal their location. As for now, research suggests that consciousness creates a 'home' within the nervous system and has the capability of taking on a prominent role in behavioral outputs, when expectations are involved.
2) Alternative and Complementary Therapies: The Placebo Effect
3) Alpha Omega Pain Medicine Associates: Placebo Power , date: 4/18/99
4) Healthline Magazine: Placebo Effects on Pain , date: 4/18/99
5) The Reward System, by Aryeh Routtenberg (located on N & B Reserve)
6) Thalamocortical Aspects of Consciousness From the Perspective of a Neurobiologist , date: 5/5/99
7) Why It Must Be Consciousness- For Real !
Mind/Brain/Behavior The Pleasing Placebo
What's the Placebo Effect?
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This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.