Capacitance (4/5) Recapitulation
Circadian biology as a template for adaptation: the matching of biological cycles to the physical world
Living Beings participate in physical cycles, which show regularity and sequentiality. These regularities are somewhat predictable, with two contrasting phases that alternate. There are four cycles known to affect the lives of all creatures:
| 1 | Circa-tidal | half a lunar day of 12.4 hours |
| 2 | Circadian | between 19 and 28 hours |
| 3 | Circa–lunar | 29.5 days (or 27.2–29.5 days) |
| This cycle partly drives the Tidal cycles. | ||
| The range of variation in luminosity is between 0.1 lux at full moon and 0.001 lux at new moon. | ||
| Daylight, by contrast typically provides >10,000 lux. | ||
| 4 | Circannual | 365.2 days |
It is from the Circannual cycle that Seasonal fluctuations emerge.35 Nested within each phase of each cycle is a smaller pulse. Just as a day has a morning, noon and afternoon, so within each part of a day there is a beginning, middle and end. On a larger scale, the alternation between night and day (with its transitional crepuscular zones) is mirrored in the alternation between summer and winter with the two transitional seasons. For us to participate in this regular sequence of events we must have within us a model, an analogue, a pattern of cyclic alternation and sequentiality. This is entrained to and by a pulse generator, situated within the hypothalamus, which maintains and constrains our responsiveness to regularity in the natural world.36 Events that impinge on living beings are, by contrast, irregular and somewhat unpredictable. Recognition of a regular background provides an adaptive advantage to living beings in that patterned information is compressible, and so allows more internal space to be freed for attention to unpredictable events. By analogy, the metronome provides regularity but not music. The internal oscillator and pattern generator found in the hypothalamus provides us with great adaptive advantage in that it allows us to discriminate between danger and opportunity. For us, danger may contain hidden opportunities while boredom and stagnation may lie within the stable environment. This interpretive faculty is highly developed in humans and lies at the heart of individual personality and group culture.
Between the two contrasting phases of the circadian or nycthemeral37 cycle to which we are most attuned lie two transitional zones: dawn and dusk, times of potential ambiguity. Ambiguity presents us with a greater processing challenge: beginning, ending, entering, exit, departure and return. Much human illness occurs during transition states. The daily cycle is nested within the annual alternation between summer and winter with the two transitional zones of spring and autumn. At such times our metabolic and endocrine settings are altered and so our capacity for adaptation will be challenged: the disturbance may precipitate illness.
Life can be viewed as a modifiable sequence of Time Series against a backdrop of uniform and unmodifiable Time. We negotiate objects in space within intervals of time. We cannot negotiate time itself but we can estimate and construct time intervals and adapt them to our perceived needs. Our ability to match these time intervals with our needs reflects our capacity for health. We are inherently receptive to pattern. Patterns become coded within us while perceptions of time intervals are modifiable by current events. Patterns allow us an abatement of vigilance: in such calm, resting states we may conserve energy. Random disturbance of background patterns heightens our attention and prepares us to react. We have a pacemaker in our hypothalamus: the Supra–Chiasmatic Nuclei. The SCN is not really a body clock though the pace may become highly attuned to a clock in a society that uses them. A clock is a precision instrument made more accurate by being unresponsive. A pacemaker, by contrast, is an approximator, made more effective by being responsive. Clock time is cultural not biological. The oscillations to which we are attuned may be tabled as follows:
| Greatest Sequential Regularity in the Environment | |
| Light | Dark |
| Matched within by Alternation in the Autonomic NS between | |
| Sympathetic (aminergic) | Parasympathetic (cholinergic) |
Against this tendency to regularity, living beings are faced with:
| Perennial Irregularity in the Environment | |
| Food & other primary needs | Potential Danger & Lack |
These irregularities may show some sequential pattern and our pattern–seeking nature may contribute to our success. As both predator and potential prey, we have two scales of focus: the near and small contrasted with circumambient vigilance: microscopic focus and cosmic imagination: a brain with left and right hemispheres. The alternation that we may experience between fear and self–confidence surely reflects our dual nature.
POISE consists in:
• Responsiveness to a wide range of signals with good buffering of noise, while at the same time retaining the ability to adjust responsiveness to prevailing changes.
• Maintenance of inclines and equivalences within the reflex arcs that are capable of being maintained over the length of the current cycle without recourse to reserves.
The model suggests that as these processes are energy–dependent, some more costly than others, Management of the economy of the trajectory will eventually correlate with subjective states.
Under the extreme circumstances of emergency, it is meaningless, even distasteful, to speak of Health. In such cases, Medicine must be dedicated to the maintenance of vital functions and the reduction of suffering. But it is equally meaningless to model Health upon Homeostasis. If Health is more than an absence of Disease and a movement away from lethal boundaries, we may speak of it as an opposite tendency: a movement towards a state that matches physical reality as the source not only of survival but of growth and development. Such a movement must be adequately resourced against unpredictable fluctuations and congruent with our capacity. Health can be seen, then, as a resolution of tension between the “to” and the “from” of life. We experience temporary irresolution as illness.
PAIN generates a positive feedback (equivalent to feed-forward) while most homeostatic mechanisms are systems of negative feedback. Illness is not an entity—injury and invasion aside—but the end of a process that once succeeded and now fails.
The parallel interlocked systems of homeostasis and circadian adaptation
The circadian “clock” resets before the dawn of each day, and is associated with a surge in cortisol at 4am, which rises steeply and peaks at about 8am. As will be shown in the table below, while homeostasis is crucial to our survival, the circadian system manages the living texture of our lives.
| Homeostasis | Circadian system |
| Maintains and buffers internal environments close to a steady point by means of negative feedback loops. These maintain each variable—notably core temperature and pH, also blood glucose and electrolytes—within narrow bounds. | Maintains the Function of the individual within Dynamic Balance by feeding forward to the day and night ahead. Unless the current event is automatised, it retains the present as a new event in short–term memory at least until nightfall. The archiving of events will happen at night along with maintenance and growth. |
| Is concerned with the current situation. | Recognises the sequentiality of Life. |
| By stabilising inner variation, homeostasis allows the organism to deal with unpredictable local variations. | Alerts the internal environment to predictable variation based upon the onset of daylight, and so marks and measures Time of Day and prepares each system for tasks and probable states ahead. |
| The values of these inner constraints oscillate narrowly in following the circadian cycle with which it communicates via the hypothalamus. | Resets the main pacemaker in the hypothalamus before the dawn of each day. Integrates and coordinates the timekeepers in each organ and every system. |
| Daily, tidal and seasonal resetting stabilises the recalibration we have to undertake in the light of experience. Facilitates the incorporation of new material and (insofar as is possible) resets adaptive capacity. | |
| Stabilises inner
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