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The placebo effect can be viewed as a form of anticipatory homeostasis. When a patient feels unwell, for example with depression, and seeks help from a trusted medical practitioner, (s)he is given a prescription. Upon receiving the medicine, (s)he anticipates feeling better and, after swallowing the allegedly curative pill, sits back and looks for the signs of increased well-being and improvement. Lo and behold, in many such cases (s)he actually does feel better, and her/his well-being is restored. If it is an active placebo with somatic side effects, then even better (Thomson, 1982). To the degree that any treatment is perceived to be effective, then expectancy must play a role. Homeopathic medicine, which has no active content by definition, provides a cogent example of anticipatory homeostasis with no harmful side effects. Homeopathic medicine is a 100% placebo masquerading as active medicine. Yet this form of medicine is used worldwide by hundreds of millions of people who swear by its efficacy.

Homeopathy has two principal ‘laws’, the first being ‘similia similibus curentur’ or ‘let likes be cured by likes’. This ‘law’ means that treatments that cause specific symptoms (e.g., onions cause runny eyes and nose) can cure conditions that cause the same symptoms (e.g., a bad cold). As if that isn’t kooky enough, there is the ‘law of infinitesimal doses’ that when treatments are diluted in water or alcohol, they actually increase in therapeutic potency. This means that a 1-in-1,000 solution should be more effective than a 1-in-100 dilution. It’s an inverted dose response curve.

The anticipatory phenomena of placebos are certainly not confined to complementary and alternative medicines. The placebo effect has wide application in all areas of medicine. There is no harm in it whatsoever, as long as one doesn’t swallow the quack claims that come along as part of the package with the pills.

Consider antidepressants. These are supposed to work by fixing a chemical imbalance, specifically, a lack of serotonin in the brain. Irving Kirsch (2015) reviews analyses of published and unpublished data that were hidden by drug companies, revealing that:

most (if not all) of the benefits are due to the placebo effect. Some antidepressants increase serotonin levels, some decrease it, and some have no effect at all on serotonin. Nevertheless, they all show the same therapeutic benefit. Even the small statistical difference between antidepressants and placebos may be an enhanced placebo effect, due to the fact that most patients and doctors in clinical trials successfully break blind. The serotonin theory is as close as any theory in the history of science to having been proved wrong. Instead of curing depression, popular antidepressants may induce a biological vulnerability making people more likely to become depressed in the future. (Kirsch, 2015: 128, italics added)

Whatever people may believe will help them to feel better may indeed help them to feel better, at least for a short while. Long-term, however, placebo effects almost always fade. This isn’t being snootily cynical. It’s a brutal fact about human nature. All the more reason, then, to apply ‘hard-nosed’, sceptical analysis to outlandish treatment claims. Carl Sagan and other wise people have suggested that ‘Extraordinary claims require extraordinary evidence’. There can be nothing more extraordinary or outlandish than the claims of homeopathic medicine. To turn our discussion full circle, there is not a single replicated piece of scientific evidence of a homeopathic remedy influencing the NS, ES or IS. The biological systems of the body carry the traces of every physical and mental stimulus we encounter. Homeopathic medicine leaves no trace. QED.

Future Research

1 Advanced imaging techniques such as ‘serial section electron microscopy’ could be applied to study the mechanisms of inflammation.

2 We need to know more about misalignments of the circadian clock, emotion, and susceptibility to inflammation and acute and chronic conditions.

3 PNI research is needed to investigate the relationships between individual differences in cognitive ability, such as IQ test scores and changes in the immune system.

4 We need more studies of the impact of psychological homeostasis on the development of physical illnesses.

Summary

1 Three important biological systems in health and illness are the nervous system (NS), the endocrine system (ES) and the immune system (IS). They activate and deactivate tissues, organs and muscles to control and regulate action, emotion and mental activity.

2 The NS uses neurotransmitters and the ES uses neuromodulators and hormones. The brain modulates the IS by hardwiring sympathetic and parasympathetic nerves to lymphoid organs. The IS modulates brain activity, including sleep and body temperature.

3 Two important classes of cell in the NS are neurones and microglial cells. Microglial cells are highly plastic and act as macrophage (‘big eater’) cells, the main form of active immune defence in the CNS.

4 Decisions made by the CNS are communicated via the peripheral NS to the effector division and inputs to the CNS are conducted by the afferent division. The autonomic nervous system deals with the non-conscious control of cardiac muscles, smooth muscles and glands, while the somatic nervous system deals with skeletal muscular responses in speech and behaviour.

5 The hypothalamo-pituitary-adrenal (HPA) axis produces corticotropin releasing hormone from the hypothalamus and conveys this to the anterior pituitary gland. The HPA axis has a primary role in emotion and stress. The amygdala triggers bodily responses to emotional events, including the release of adrenalin by the adrenal glands.

6 The endocrine system consists of the ductless glands and the hormones produced by those glands. Endocrine glands release their secretions directly into the intercellular fluid or into the bloodstream. Cellular metabolism, reproduction, sexual development, sugar and mineral homeostasis, heart rate and digestion are all regulated by hormones.

7 The ES regulates the circadian rhythm and sleep/waking cycle with a variety of hormone releases. Melatonin is produced in the pineal gland, under the control of the central circadian pacemaker in the suprachiasmatic nucleus (SCN) region of the hypothalamus.

8 The IS protects the body against disease or other potentially damaging foreign bodies. When functioning properly, the IS identifies and attacks a variety of threats, including viruses, bacteria and parasites, while distinguishing them from the body’s own healthy tissue.

9 Psychoneuroimmunology is the study of the interactions and relationships between psychological, neurological and immunological processes. Research over recent decades suggests that brain-to-immune interactions are highly modulated by psychological factors which influence immunity and IS-mediated disease.

10 The principle of physiological homeostasis is extended to psychological homeostasis. Identical mechanisms exist in both forms of homeostasis. In seeking to maximize physical and subjective well-being to a high set point, we approach new sources of potential reward and try to avoid aversive or confrontational situations.