Chronobiology: dialectic of the temporal and the biological

Jeremy Campbell indicates that Einstein had removed time and space from their traditional metaphysical pedestal of unchanging absoluteness. In other words, the effect of relativity theory was to physicalize space and time. As a result, time and space became fluctuating components of the physical universe capable of entering into dynamic interactions with other facets of that universe.

Just as time was physicalized through the efforts of Einstein, Campbell contends time has been " biologized and psychologized" through the work of a variety of recent experiments and explorations. According to Campbell, just as Einstein seemed to show that time interacted with the motion of a given system, biologists have been introducing experimental data indicating biological clocks are affected by the conditions of life which surround such clocks.

When Einstein physicalized space and, especially, time, he was culminating, as well as transforming, a process popularized by Galileo (though this process did not begin with the latter). Galileo treated time as a continuous and uniform entity which could be represented by a straight line. Thus, time was construed in a spatialized manner within a mathematical framework.

As such, time came to be treated as if it were a fourth spatial direction which is continuous in the same way that space is supposed to be continuous. In other words, both space and time were alleged to consist of an infinite number of points, all of which can be mapped on to the real number line.

Consequently, the modern conception of time has deviated rather substantially from the idea of time which had prevailed for nearly 2000 years. In the traditional view, time was considered to be some sort of absolute master clock which was independent from all of physical/material reality. Today, time has become just another component of the physical world which is capable of fluctuating under a variety of conditions.

However, all of these changes in the way in which time is, and has been, conceived may be more a reflection of the way time is methodologically engaged than they are a reflection of the structural character, or actual ontology, of time. In other words, what really may have changed in the last 2000 years is the way in which time is methodologically engaged.

These transitions in methodology have led to comparable transformations in the way that time is conceptualized. None of these changes, however, necessarily has anything to do with giving insight into the ontology of time.

Zeitgebers: extrinsic and intrinsic

Organisms are not only oriented in space, they are also oriented in time. Chronobiology is the science which studies the role that temporality has in biological functioning. A great deal of relatively recent experimental findings suggests there are innate mechanisms in a large number of species of organisms which give expression to a variety of temporal rhythms. These rhythms regulate different facets of biological and behavioral processes in various species.

For example, consider animals living in burrows. Such animals have an internal, biological clock which is entrained by the temporal rhythm of alternating patterns of night and day.

Each day, the internal, biological clocks of these animals are reset to reflect the changing relationship of the ratio of daylight hours relative to nighttime hours. When they wake up in the morning, their internal clocks, not the light of day, has awakened them.?

Franz Halberg introduced the term circadian rhythm to describe those instances of temporal entrainment, such as in the case of the burrow animals mentioned above, that are based on a period lasting roughly one day. The alternating cycle of day and night acts as a zeitgeber or 'time giver' which an organism uses as a temporal frame of reference to set its circadian biological clock.

When an organism is disentrained - that is, when an organism is unable to make contact with the temporal frame of reference provided by the relevant zeitgeber (in this case, the alternating cycle of day and night), such a disentrained organism will operate on the basis of the intrinsic properties of its internal biological clock. This clock, left on its own without any external standard by which to set itself, will run either somewhat longer than a 24-hour period, or somewhat shorter than a 24-hour period.

Organisms entrained by various kinds of temporal rhythms, of which circadian rhythms are but one example, do more that just reset their internal clocks to synchronize with various rhythms of the external world. Entrainment means virtually every biological process which goes on in a given organism will have a determinate phase relationship with events occurring both in other parts of the body, as well as in various aspects of the external world.

The phenomenon of diapause is an example of how the behavior of an organism can be governed by the phase relationships which the biological clock of that organism establishes with respect to certain features of the external world. Diapause refers to the period of inactivity or quiescence exhibited by many insects during relatively regularly occurring periods of detrimental weather conditions, such as drought or winter weather.

However, the preliminary stages of diapause occur much in advance of the forthcoming, adverse weather conditions. Insect activities such as the storing of food or the building of shelters are steps that are preparatory in nature and which take place independently of any specific stimuli of drought or cold or snow.

The preparatory activity is an expression of the phase relationships which exist among: (a) certain biological clocks of the insect; (b) various motor systems in the insect, and (c) the changing ratio of sunlight to nighttime. As the character of these phase relationships changes, behavioral patterns emerge which are preparatory to the later set of phase relationships which constitute diapause proper - that is, the actual period of quiescence.

Therefore, biological clocks are part of a system which enables an organism to grasp (although not necessarily on a conscious level or in a self-reflexive manner) the character of a changing set of phase relationships in the dialectic between organism and environment. In a sense, there is a process in which certain rules of temporality are internalized. These rules have the effect of placing constraints on the freedom of an organism to act.

Rules versus principles

From the perspective of the present article, the internalization of rules of temporality is not really an accurate way of describing the situation. More specifically, the organism consists of a spectrum of ratios of constraints and degrees of freedom. This spectrum establishes a set of parameters within which, and through which, the organism is capable of responding or manifesting itself under appropriate circumstances of dialectical interaction with the environment.

Although phase information may be exchanged, and although the effect of this exchange of phase information may bring about a transition in the aspect of the organism's spectrum of ratios which is being manifested, no rules, temporal or otherwise, are internalized by the organism. A principle is activated, instead, through the dialectical activity.

The term "principle" refers to certain kinds of ratios of constraints and degrees of freedom. Such ratios may be manifested in the form of hermeneutical point-structures, neighborhoods, or latticeworks (see the ‘Glossary of Terms’ in the ‘Overview’ article within the Education Folder in ‘Food For Thought’).

What makes a given ratio of constraints and degrees of freedom, or set of such ratios, a principle has to do with the structural character of the phase relationships which exist in the ratio(s). A principle consists of a set of phase relationships which form an attractor basin.

The attractor basin may be either linear or chaotic, depending on the nature of the principle. However, usually speaking, principles involve chaotic attractors, not linear attractors.

Rules, when they do arise, tend to be associated with linear attractors. Such attractors are fairly, narrowly defined and do not permit much, if any, deviation from the scope of the parameters that describe a rule.

Principles, on the other hand, provide a basis for a far more sweeping range of possibilities. All such possibilities are self-similar, rather than self-same.

Consequently, principles are capable of being receptive to, as well as of responding to, nuances and variations that fall beyond the largely linear horizons of a rule. Nonetheless, despite such variability, all these self-similar possibilities fall within the structural parameters of the chaotic attractor to which they give expression.

The principle(s) inherent in a given biological clock form an attractor basin which is sensitive to, and shaped by, certain kinds of phase information being relayed to the basin(s) as a result of the organism's engagement of, and engagement by, different aspects of the environment. In other words, the presence of certain kinds of phase relationships induces shifts or transitions in the way the attractor basin/principle gives expression to itself. As a result, the principle, in this case a biological clock, is activated.

Subsequent behavior which is generated in, or which is colored by, such an attractor basin, will conform to the parameters of constraints and degrees of freedom that have been established by means of the activated principle/attractor basin. Moreover, since the activated attractor basin/principle is sensitive to, and shaped by, the changing character of the phase relationships in the dialectic between organism and the environment, those behavioral patterns that are influenced by such an attractor will reflect the shifts in phase relationship information.

In short, certain aspects of the organism's behavior become entrained by transitions in phase relationship. Thus, although no rules have been internalized, principles have been set in motion and behavior has been affected as a result of the dialectical engagement between organism and environment.

The question of master biological clocks

In the early 1970s, a certain amount of excitement was generated when a number of biologists believed they had discovered a master biological clock. Such a clock is supposed to be autonomous and independent of all external, temporal cues. In addtion, a master biological clock is theorized to be responsible for generating all the different rhythms of the body.

The would-be master clock discovered in the 1970s is located in the frontal portion of the hypothalamus. It consists of several clusters of cell groups which have become linked during the course of development. The technical term for these coupled cell clusters is suprachiasmatic nucleus - or, SCN, for short.

Two properties, in particular, of the SCN seemed to enhance its attractiveness as a candidate for the master clock. First of all, the coupled nuclei of the SCN display a great deal of oscillatory activity. Oscillatory behavior is something one would expect to observe in any candidate for a master clock since the clock is responsible for regulating a wide variety of rhythmic patterns.

Secondly, the suprachiasmatic nuclei are connected, via a nerve tract, to the retina in each eye. One obvious implication of this link is that the SCN would be able to receive important data concerning temporal rhythms in the external world. Especially important in this regard would be those rhythms involving the changing pattern of the ratio of daylight to nighttime as one progressed through the year.

Subsequent experiments, in which the SCN were removed, indicated the master clock had not been found. These experiments showed that although the temporal identity of an organism is significantly altered when the SCN are removed, nevertheless, temporal identity was not destroyed. In other words, while the SCN seemed to play a fundamental role in synchronizing various biological rhythms, they were not responsible for generating these other rhythms. Consequently, there must be other biological sources which are underwriting temporal identity.

Although the suprachiasmatic nuclei do not constitute ' the' master biological clock, they are believed to be the locus within which one of two master clocks can be found. Together, these two clocks are considered, by many chronobiologists to be responsible for regulating the vast majority, if not all, of the biological rhythms in the human body. These rhythms range from: the secretion of growth hormone, to cycles of activity and inactivity, to establishing the point in the sleep cycle when vivid dreams are most likely to occur, to the rise and fall of core body temperature, and so on.

The location of the second master clock has not yet been established. However, this second clock is thought to be the more stable, as well as the more powerful, of the two clocks.

Nevertheless, this second, more stable and powerful, master clock is believed not to have any direct contact with the changing patterns of light to darkness ratios. Therefore, this second clock may be entrained by the so-called master clock thought to be located in the suprachiasmatic nuclei, since this latter "master" clock is in contact, via nerve tracts extending to the retina, with external data concerning the changing ratio of light to darkness.

There are some chronobiologists who do not accept the two-master-clock hypothesis. They believe there may be a number of other "master" clocks in addition to the two already mentioned.

For example, there is considerable evidence pointing toward the adrenal gland as the locus for, yet, another clock of sorts. More specifically, one of the hormones secreted from the outer cortex of the adrenal glands is cortisol.

Cortisol plays a fundamental role in the way the body responds to stressful situations. Fluctuations in the level of cortisol secretion appear to follow cyclical rhythms during the course of the day.

The adrenal-clock, however, is not necessarily a master clock. Quite frequently, a given biological system will have an intrinsic periodicy which characterizes its biological activity. This innate periodicy is not, in and of itself, a master clock. Such inherently periodic systems are known as a tau.

The structural character of a tau gives expression to certain aspects of an underlying genetic blueprint. Although a tau's general structural character is species specific, the individual members of a species will display a tau which is similar to, but not precisely the same as, the average value for the species with respect to that tau.

Human beings, along with a variety of other species, are capable of being entrained, simultaneously, to a variety of different biological clocks. On the other hand, human beings are also capable of having some of their biological rhythms synchronized with others with whom they live in close contact over a period of time.

Some hormones play a role in communicating, to various systems in the body, information concerning the temporal phase of external rhythms. These hormones are referred to as temporally active hormones.

These sort of hormones are believed to keep different circadian systems in touch with the fluctuations occurring in various rhythmic patterns in the external world that are relevant to the body's circadian rhythms. In human beings, there are a variety of temporally active hormones providing humans with a number of different sources of temporal information.

As a result, such hormones help establish a spectrum of ratios of constraints and degrees of freedom with respect to the way a human being can engage the environment in a temporal dialectic. Furthermore, although the general number and structure of biological clocks is pretty much the same from one human being to the next, there can be a great deal of variance in how these different clocks are linked together in different individuals. In other words, different individuals will exhibit different patterns of synchronization with respect to how the clocks will be linked to one another.

Sometimes these differences are a result of genetic inheritances. Sometimes the differences in patterns of synchronization are due to the kind of life the individual leads. Finally, sometimes a combination of the two foregoing factors will lead to differences in patterns of synchronization from individual to individual.

A spectrum of biological rhythms

Modern high-speed computers have taken on a function, with respect to biological rhythms, somewhat similar to the role that a prism played with respect to light waves. Just as a prism is able to show visible light is an aggregate of a number of different wavelengths of light, so too, modern computers have been able to show there is a spectrum of biological rhythms underlying an organism's activity.

Through the application of computer and inferential statistical techniques, approximately seven to eight basic types of rhythms have been discovered so far. They are: ultradian (less than 20 hours); circadian (between 20-28 hours); circasemiseptan (31/2 days); circaseptan (7 days, plus or minus 3); circadiseptan (14 days, plus or minus 3); circavigintan (21 days, plus or minus 3); and, circannual (1 year, plus or minus 2 months). The term infradlan is used to refer to cycles lasting longer than 24 hours.

Circaseptan rhythms (which have a period of approximately 7 days) are showing up in a variety of biological processes. Generally speaking, these rhythms are of low amplitude and, therefore, are hard to detect amidst the higher amplitude, more prevalent circadian rhythms. However, although, on an individual basis, the circaseptan rhythms are weaker than the circadian rhythms, over the course of a week, the aggregate collection of circaseptan rhythms has a large amplitude.

While circaseptan and circasemiseptan rhythms do not appear to reflect any external temporal rhythm, these rhythms are not arbitrary. They have a harmonic relationship with such external rhythms as the cycle of day and night, as well as the lunar cycle.

Thus, the rhythms associated with various biological functions (such as growth, maturation, cell maintenance, reproduction, immune responses, and so on) will be a complex harmonic function of the way entrainment properties of external rhythms dialectically interact with the vectoring properties of innate biological currents such as the circaseptan and circasemiseptan rhythms. However, nobody in the field of chronobiology knows, yet, what the structural character of this dialectic is or what the harmonic laws are which govern that dialectic.

One can differentiate between music and noise by noting how the former consists of a set of sound waves which have an ordered, structured relationship with one another. In the case of noise, the aspect of orderly relationship is missing.

In music, a given complex sound is a function of a set of simple waves which are whole-number multiples of some fundamental, lowest frequency, wave component inherent in the given complex sound. This lowest frequency wave component is known as the first harmonic. Depending on the sort of whole-number multiple a given wave component has relative to the frequency of the first harmonic, the other wave components of a complex musical sound will be referred to as harmonics of the second, third, fourth, etc. order.

Some of the more complex temporal rhythms (e.g., circannual or circavigintan , etc.) may be whole-number multiples of some of the simpler rhythms such as the ultradian or the circadian. Thus, the more complex biological rhythms could be seen to be higher order harmonics of the basic temporal units.

Light, melatonin and circadian systems

Just as light plays a fundamental role in Einstein's special theory of relativity, light also plays a fundamental role in chronobiology. Light is the standard to which the body refers in order to re-gauge its biological rhythms so they can be synchronized with, among other things, the primary circadian rhythms generated by the alternating cycle of night and day.

Although most of the light impinging on the individual's eye is transduced into visual signals, a certain amount of the light serves as a source of temporal information concerning the external rhythm of the cycle of day and night. This information is passed on to the suprachiasmatic nuclei in the hypothalamus. These nuclei are linked with a variety of other biological clocks and taus. The end result of this dialectic is to permit the organism to get into an appropriate phase relationship with external rhythms.

The pineal gland is known as a neuroendocrine transducer. This means it is capable of converting or translating the action potentials of the nervous system into the secretion of various kinds of hormones. One of the hormones transduced by the pineal gland in this fashion is melatonin.

The suprachiasmatic nuclei is connected to the pineal gland by means of a nerve tract. By sending certain messages along this nerve tract to the pineal gland, the SCN is able to control the quantities, and, therefore, activity, of a particular enzyme in the pineal gland. The enzyme regulated by the SCN plays a role in synthesizing melatonin from a precursor neurotransmitter, serotonin.

Although the precise role of melatonin is not presently known, it is deeply implicated in the body's circadian system which is hooked into external rhythms of night and day. The levels of melatonin secretion are highest between the hours of 11 at night and 7 in the morning. Alternatively, the levels of melatonin secretion are lowest during the hours of waking activity.

Apparently, light serves as a signal for the suppression of melatonin secretion, whereas nighttime acts as a stimulus leading to the synthesis of melatonin. The rhythmic rise and fall of melatonin levels is a waveform which is propagated throughout the body.

This cyclical waveform plays a role in the synchronization and harmonious interaction of a variety of biological rhythms. Furthermore, while the amplitude, frequency and phase of this wave can be affected by altering the timing and/or intensity of the organism's engagement with light stimuli, each species has its own characteristic way of responding to such alterations in the character of light stimuli.

Almost all vertebrates come equipped with a pineal gland. Although the function and the size of the pineal gland varies from species to species, generally speaking, the more critical the role(s) which is(are) played by temporal rhythms in a given vertebrate species, the larger will be the size of that species pineal gland. In addition, in many of, if not most of these vertebrate species, fluctuations in the level of melatonin synthesis and suppression in the pineal gland are linked to the way the organism establishes phase relationships with external cyclical patterns such as day and night, as well as summer and winter.

In the latter case, the nervous system may have some sort of mechanism for both: (a) keeping running totals of the ratio of melatonin synthesis to melatonin suppression and, then, (b) coupling (a) with a process that compares the latter ratio against some innate or learned (such as through critical periods) standard. This mechanism allows the organism to make fairly complex preparations for forthcoming seasonal changes.

The suprachiasmatic nuclei is also linked with the lateral geniculate nucleus. The primary neurotransmitter propagated along the nerve tract connecting the SCN and the LGN is known as neuropeptide Y.