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From time to time, novel ways of interpreting and modifying ageing mechanisms are proposed. Occasionally, these lead to a conceptual dead end, whereas at other times new and vital insights into basic ageing mechanisms are gained. This review concentrates on one such way of interpreting and manipulating ageing processes, based on chaos (dynamical systems) theory. One prediction of this theory is that a wide-ranging loss of physiological complexity from molecular to cellular, and from tissue to organismic levels accompanies ageing and age-related diseases. Although this view has been criticised, and arguments have been put forward to claim that there is also an increase of complexity during ageing and dysfunction, this review holds that the interpretation of ageing as a simplification of physiological dynamical complexity offers clear advantages. Ageing changes can be quantified and the results of treatment monitored. Clinical benefits can be predicted and intervention strategies improved. Two main practical suggestions for achieving successful ageing at the clinical level are examined. First, chaos theory challenges the traditional pharmacological regimes and implies that, for maximum benefit, medication aimed at modifying some of the signs of ageing should be given at irregular, pulsed or multiple intervals, and at constantly changing dosage strengths. Second, for preventing age-related disability, it is necessary to introduce and maintain a multiplicity of external and internal physiological stimuli, such as variable physical and mental exercise regimes.

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Hormesis is a term describing the beneficial effects of mild and repeated stimulation or stress, which ultimately bolsters defences against deleterious processes. Although hormetic influences are clearly encountered at the cellular and molecular level, little is known about the effects of hormesis at a clinical level. This paper examines the suggestion that mild stimulation or appropriately timed challenges may be used clinically in order to influence the impact of age-related disease and dysfunction. Examples of stimulation or challenges that may exhibit hormetic effects include dietary restriction, physical and mental exercise, and even social and spiritual stimulation. Dietary restriction places the organism under nutritional stress, stimulating several biochemical repair pathways that may counteract certain age-related changes. Physical and mental challenges, if appropriately timed and sufficiently varied, are directed at increasing the complexity and integration of interacting muscular, cardiovascular, and neural stimuli. Social and spiritual stimulation aimed at reversing age-related loss of dynamical complexity acts upon even higher levels to ensure a reduced risk of social problems in aging.

The pace of technology is steadily increasing, and this has a widespread effect on all areas of health and society. When we interact with this technological environment we are exposed to a wide variety of new stimuli and challenges, which may modulate the stress response and thus change the way we respond and adapt. In this Opinion paper I will examine certain aspects of the human-computer interaction with regards to health and ageing. There are practical, everyday effects which also include social and cultural elements. I will discuss how human evolution may be affected by this new environmental change (the hormetic immersion in a virtual/technological environment). Finally, I will also explore certain biological aspects which have direct relevance to the ageing human. By embracing new technologies and engaging with a techno-social ecosystem (which is no longer formed by several interacting species, but by just two main elements: humans and machines), we may be subjected to beneficial hormetic effects, which upregulate the stress response and modulate adaptation. This is likely to improve overall health as we age and, as I speculate here, may also result in the reduction of age-related dysfunction.

The process of aging is accompanied by a progressive reduction of biological dynamical sophistication, resulting in an increased probability of dysfunction, illness, and death. This loss of sophistication is inherent in all aging organisms. However, it may be possible to retard the rate of loss of biological complexity by introducing an increased amount of nonlinear, nonmonotonic external stimulation that challenges the organism and forces it to upregulate its biological processes. This can be achieved by exploiting the multiple effects of hormesis, through a wide range of challenges including physical, mental, and biological stress. Hormesis is widely encountered in biological systems, and its effects are also seen in humans. It is possible to use hormetic strategies (both conditioning hormesis and postexposure conditioning hormesis) to enhance the function of repair processes in aging humans and therefore prevent age-related chronic degenerative diseases and prolong healthy lifespan. Such techniques include dietary restriction and calorie restriction mimetics, intermittent fasting, environmental enrichment, cognitive and sense stimulation, sexuality-enhancing strategies, exposure to low or to high temperatures, and other physicochemical challenges. Current research supports the general principle that any type of a hormetic dose-response phenomenon has an effect that does not depend on the type of stressor and that it can affect any biological model. Therefore, novel types of innovative, mild, repeated stress or stimulation that challenge a biological system in a dose-response manner are likely to have an effect that, properly harnessed, can be used to delay, prevent, or reverse age-related changes in humans.

Artificial, neurobiological, and social networks are three distinct complex adaptive systems (CAS), each containing discrete processing units (nodes, neurons, and humans respectively). Despite the apparent differences, these three networks are bound by common underlying principles which describe the behaviour of the system in terms of the connections of its components, and its emergent properties. The longevity (long-term retention and functionality) of the components of each of these systems is also defined by common principles. Here, I will examine some properties of the longevity and function of the components of artificial and neurobiological systems, and generalise these to the longevity and function of the components of social CAS. In other words, I will show that principles governing the long-term functionality of computer nodes and of neurons, may be extrapolated to the study of the long-term functionality of humans(or more precisely,of the noemes, an abstract combination of 'existence' and 'digital fame'). The study of these phenomena can provide useful insights regarding practical ways that can be used in order to maximize human longevity.The basic law governing these behaviours is the 'Law of Requisite Usefulness', which states that the length of retention of an agent within a CAS is proportional to the agent's contribution to the overall adaptability of the system.