While you might ascribe those feelings to activity, work, food and a host of other issues, there's another factor few people consider. It's called our "biological clock" and it roughly follows the cycle of a solar day. Hence, we refer to this biological rhythm as "circadian."

Although slightly inaccurate, our biological clocks are actually capable of keeping fairly accurate time over the long run. Even without external cues, our circadian rhythms vary as little as a few minutes per cycle. Such accuracy is not inherent to humans only - lower life forms also have precise built-in timekeepers.

Over the course of the last few decades, scientists have learned a great deal about biological rhythms from animal and human studies. We now know that the central mechanism of our clock is located in what is termed the Suprachiasmatic Nuclei, a brain region within the hypothalamus. Firing patterns of roughly 10,000 or more specialized nerve cells in this region send precise signals to specific brain areas which trigger a host of biological responses. These include changes in blood pressure, temperature, hormone levels, behavior and you guessed it wakefulness. It's not surprising that damage to these cells caused by certain diseases or tumors predictably scrambles our ability to maintain biological balance and rhythm.

The basic precision of our biological clock is set by only a relatively small number of identified genes. This genetic material triggers the expression of proteins that tell these cells when to fire. Despite this programming, the clock is not perfect and some tendency to wander exists.

Just as you might reset your wristwatch each day (especially if you have an older analogue model), cells of our internal pacemaker require some adjustment as well. Not surprisingly, this brain region is in close proximity to our eyes which provide signals that send small daily adjustments to our clock. In effect, variations in light serve to synchronize our circadian rhythms. This finding becomes particularly important in conditions such as jet lag and shift work where a change in visual clues has the tendency to desynchronize our inner clock.

As we proceed to explore this issue, the question that immediately surfaces is whether or not long-term biological time-keeping is maintained in this area of the brain. For many animals, this is certainly the case, as patterns of hibernation and migration are dependent on this system. In humans, however, the evidence is compelling yet not fully understood. It is believed that peaks in the hormone Melatonin, a substance secreted by the brain's pineal gland (and directly controlled by these neurons) condition what is often referred to as an "internal endocrine calendar." Supporters of this perspective offer examples such as mood change and depression during the winter months which seems to be improved in some individuals with the use of bright artificial lighting.

We now know more about the influence of Melatonin on circadian rhythms based upon a research study recently published in the New England Journal of Medicine (October 12, 2000). R. L. Sacks and colleagues of the Oregon Health Sciences University in Portland studied circadian rhythms in people who were totally blind. These individuals often have free-running biological rhythms that are not synchronized to environmental cues. It should be noted that unsynchronized cycles are thought to be associated with recurrent insomnia (difficulty sleeping) and daytime sleepiness.

The researchers attempted to regulate their cycles. They gave 7 people either 10 mg. of Melatonin or placebo (a sugar pill used to control the experiment) daily (1 hour prior to their preferred bedtime) for a period of 3-9 weeks. In 6 of 7 individuals who received Melatonin, their circadian rhythms were precisely set to a 24 hour cycle.

This experiment does not suggest that everyone with insomnia should rush out and stock up on Melatonin. A variety of causes for disordered sleep are known to exist. Relying on Melatonin when other issues have not been explored makes little sense. This study does, however, demonstrate that Melatonin (used for short periods) can potentially benefit individuals who do not receive daily visual light clues that serve to adjust our internal clocks.

As our understanding of the nature of circadian rhythms expands, it's likely we'll see major breakthroughs on many medical fronts ranging from therapies for individuals with mental illness to improved pharmacological regimens based upon optimal dosage timing.

The bottom line is simple. Quality of life and survival depends to a great extent on an internal timepiece that doesn't require winding or batteries. In the long run, however, it may depend on how we take care of ourselves.

If you've ever wondered why you are a "night owl" or an "early bird," perhaps now you have a better understanding of what really makes you tick - Mind Over Matter!