Homeostatic mechanisms maintaining a complex biopsychosocial equilibrium are central to my theory of rehabilitation. When I first thought of homoeostasis in that context, I did not realise how long ago the ideas had been suggested. My published paper does include some references and evidence. This paper discusses the issues in more detail, including a historical perspective. Understanding homeostasis and its central role in a person’s life will assist when offering rehabilitation to enhance their natural adaptation. The process concerns the goals someone has, and these are considered in the next page in this series of pages, expanding on the general theory of rehabilitation.
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from Aristotle’s time (2,300 years ago) and probably much before. The humoural theory suggested each person had four humours (meaning fluids): black bile, blood, phlegm, and yellow (or black) bile. These four humours had to be balanced, the balance being unique to each person. They were part of a more complex theory that mixed Aristotle’s four elements and Galen’s four humours.
The importance of mechanisms to set and maintain constancy in some parameters is more recent. Dennis Bernstein gives a fascinating description of Feedback Control: An Invisible Thread in the History of Technology. One of the early mechanical mechanisms related to timekeeping, a verge-and-foliot mechanism that controlled the rotation of an axle, was developed around 1283. It was 500 years before the following significant automated feedback control mechanism was developed. This was the governor, first described in 1788. The steam engine was the crucial need driving this invention, but they were also designed for waterwheels, windmills, phonographs, etc. During the nineteenth and twentieth centuries, feedback mechanisms were developed across many technologies.
In July 1929, Walter B Cannon reviewed the historical development of ideas about feedback control in humans, and I have taken a few examples from his paper. The existence of biological feedback mechanisms was recognised as early as 1877 by EFW Pflūger, who said, in German, “The cause of every need of a living being is also the cause of the satisfaction of the need.”.
Similarly, in 1885, L Fredericq said, “The living being is an agency of such sort that each disturbing influence induces by itself the calling forth of compensatory activity to neutralize or repair the disturbance. The higher in the scale of living beings, the more numerous, the more perfect and the more complicated do these regulatory agencies become. They tend to free the organism completely from the unfavorable influences and changes occurring in the environment.”
Claude Bernard, a French physiologist, set out the crucial importance of a stable internal physiological state in 1878, “It is the fixity of the ‘milieu interieur’ which is the condition of free and independent life,” writing a few pages later, “all the vital mechanisms, however varied they may be, have only one object, that of preserving constant the conditions of life in the internal environment.”
In 1900, C Richet, a Frenchman, summarised matters succinctly: “The living being is stable.”
This page considers how stability is maintained.
The word homeostasis was coined by Walter Cannon in 1926, combining the Greek homoios, meaning ‘the same’ with stasis, meaning constancy (not a fixed static state, but a varying state which is kept constant). As George Billman wrote, it describes “the self-regulating processes by which a biological system maintains stability while adjusting to changing environmental conditions.”
In their article, A physiologist’s view of homeostasis, Harold Modell and colleagues give five critical features needed by any homeostatic system must have:
- A sensor to measure the regulated parameter,
- A mechanism to determine the set point, the value of the controlled parameter that the system should achieve and maintain. This value may change.
- An error-detection mechanism to detect the discrepancy between the set point and the observed value,
- A control mechanism that uses the measured discrepancy to produce outputs needed to return the variable’s value towards the set point.
- Effector mechanisms that can enact the changes needed.
The homeostatic process is constantly active, even if the system is stable and at the set point.
Homeostasis originated in physiology and is usually associated with it. However, the mechanism and the concepts are universal. Maintaining a stable state, fluctuating around an average in response to changes outside or within the system, occurs in many circumstances, in biology, social structures, populations, finances, etc.
The reach and relevance of homeostasis have been overlooked, by me at least. For example, we have a physiological system for maintaining our body temperature through shivering or sweating. However, should these mechanisms be insufficient, we will behave differently. We will take off or put on clothes, light a fire, open a window, move into the shade, etc. All these behaviours are semi-automatic and aimed at maintaining our body temperature. Our biochemical milieu requires food and fluid. A low blood sugar or dehydration, mediated by feelings of thirst or hunger, will change our behaviour.
Thus, our essential physiological homeostasis requires more than an internal, biochemically mediated mechanism alone. It requires changes in our behaviour, and most homeostatic mechanisms alter our behaviour.
The concept of balance in life is most apparent when discussing work-life balance. However, many people do not work, yet everyone, including children, must find a balance. Moreover, a dichotomy of work and non-work is inappropriate in many circumstances. For many people, women in particular, the domestic demands arising at home mirror the demands made at work, and they have an unbalanced life with too much time spent responding to the needs or demands of others and too little time to satisfy their own needs.
A better approach will look at human needs; one example is Maslow’s classification of human motivational needs. This will be discussed in detail on another page in this series concerned with the General Theory of Rehabilitation. For the moment, I will refer to the non-physiological homeostatic processes as examples of biopsychosocial homeostasis.
In 1942, John Fletcher wrote an article on Homeostasis as an explanatory principle in psychology; he encompassed several aspects of psychology in his piece, including perceptual constancy and a person’s status, both physiological and social. In 1966, Radhakamal Mukerjee also suggested homeostasis was widespread across many domains of human society. However, although they put forward arguments from first principles, these two authors did not produce evidence or suggest mechanisms.
In 1985, Alex Michalos published his Multiple Discrepancies Theory (MDT, but not multidisciplinary team!), available from ResearchGate. The theory suggests that people aim to optimise their net life satisfaction. He has six hypotheses, but the main two are.
- Reported net satisfaction depends upon perceived discrepancies between a person’s present situation and what:
- they want,
- relevant others have,
- the best they had in the past,
- they expect in the next three years,
- they hope to have, after five years,
- they think they deserve and need.
- Pursuing and maintaining net satisfaction motivate people, and the drive is proportional to the perceived benefit.
The areas of need influencing satisfaction will be discussed on another page. At this point, one should note that subjective well-being, a concept close to net satisfaction, is closely related to how well Maslow’s five areas of human need are met.
In summary, the idea that people strive for and maintain a stable equilibrium within limits in all areas of their lives has been put forward several times over many years. While this does not prove the theories are correct, it does support further exploration.
Evidence on homeostatic processes.
We have noted that longer-term fluid and nutritional balance stability is maintained by changing behaviour and that similar mechanisms apply to body temperature. These needs are through intermediate drives of perceived feelings of thirst, hunger, or cold.
We feel other needs, albeit with a less strong imperative to act. For example, we may feel lonely, bored, that others do not appreciate our status, or that we need a more significant income to feel secure. All these feelings can lead to a conscious change in behaviour.
In his General Theory of Behaviour, David Marks develops, with evidence, the idea of biopsychosocial homeostasis. He suggests a central homeostatic neural network determines the set points (targets) for various needs and measures the discrepancy between actual status and the set point. It alters behaviour to reduce the discrepancies. There is some evidence to support this theory.
Brian Edlow and colleagues studied six healthy people and identified neural networks connecting the brainstem and forebrain, especially the medial temporal lobe. This could be part of the Central Homeostatic Network. At this stage, the existence of a structural network cannot prove its function, but it does make the hypothesis plausible.
Sheri Mizumori and Yong Jo extensively reviewed the evidence in 2013. They suggested that the hippocampus played a vital role in adapting behaviour by comparing actual and expected outcomes. The discrepancy worked through other networks to maintain stability.
Social homeostasis, the avoidance of loneliness, was studied in rats by Gillian Matthews and Kay Tye, who reviewed social homeostasis, especially in rats exposed to acute social isolation. They discuss how social isolation is detected and responded to.
They also reviewed the attributes of a social homeostatic system. First, the social system must be flexible, considering other demands, such as hunger, that may have priority. Second, it might share its processing with other homeostatic networks or be a dedicated network; the former would facilitate setting priorities. Third, they argue that the subjective experience of loneliness may be necessary to draw attention to a state threatening health (see blog post on loneliness) and allow the individual (rat or person) some control. Fourth, they discuss valence, the issue of positive or negative motivational drives.
Their theory was extended to include chronic situations, such as long-term social isolation, by Christopher Lee and colleagues. Karen Bales and colleagues have explored the model, discussing how many factors will influence each person’s set point.
Emotional homeostasis has also been studied. John Montgomery has written a theoretical article reviewing the evidence for emotional homeostasis and speculating that some mental health difficulties arise from homeostatic mechanisms that evolved to respond to natural events in natural environments that are inappropriate in modern circumstances.
The mechanisms maintaining emotional stability may depend upon the autonomic changes associated with emotional states. Kenji Kanbara and Mikihiko Fukunaga discuss this hypothesis. Coincidentally, in the same year (2016), Irina Strigo and Arthur Craig published evidence derived from monkeys and humans. They identified appropriate neural pathways and found expected changes in the insular and cingulate cortices in humans subject to experimental manipulation of homeostatic processing.
In summary, plausible homeostatic mechanisms exist in humans and animals to account for social and emotional homeostasis. All homeostatic mechanisms will work through altering a person’s behaviour.
Humans, like other living things, aim to maintain stability. While this is most obvious when considering physiological aspects of bodily function, the principle applies universally. Within acceptable limits, stability is supported by a feedback mechanism that responds to change away from the desired goal in a way that reverses the change. This applies to mechanical systems like steam engines, electronic systems, and biological systems, where it is called homeostasis.
In people, physiological homeostasis has been well-studied. The functions being controlled are vital to life; significant deviation might cause death, and the mechanisms are quick-acting. However, many other crucial aspects of a person pose less immediate threats to life and significantly impact well-being or quality of life. The responses are much slower but are longer-lasting. They mainly involve changes in behaviour.
Moreover, stability may be maintained by adjusting the target, either the controlled phenomenon or the setpoint level. This contrasts with physiological parameters, where the target level is fixed.
Detailed studies of the neurological mechanisms in man or animals are at an early stage. However, it is apparent that there are mechanisms and that constructs such as social interaction are subject to homeostasis. Further, there is evidence that changing the set point or phenomenon of interest occurs in people. Further research should enable the design of more effective rehabilitation interventions.
Living things aim for stability. Events disturb stability. Therefore, living things have evolved mechanisms to respond to change and restore stability. This is the general principle of homeostasis, which is well-established for bodily physiological phenomena. Bodily homeostasis must work in short timeframes, but most other parameters leave more latitude. Physiological mechanisms are entirely within the body, whereas all other mechanisms involve the person or living thing interacting with their environment, including others. The principle of homeostasis has been applied to many areas of a person’s life and, indeed, to complex aspects of an animal’s life. Evidence suggests that complex phenomena such as social interaction are subject to homeostasis. Therefore, it seems reasonable to assume that most aspects of a person’s life are subject to a homeostatic process, one which can be influenced consciously but does not depend upon a person’s active control.