Understanding Your Internal Clock

I am sure you roughly understand the concept of your “internal” biological clock. Indeed, most every living creature, from single-celled organisms up to complex animals have some sort of automated function which keeps them in tune with the normal ebbs and flows of time. Sunflowers know how to direct themselves toward the sun. Flowering plants know when to open themselves to receive light and make themselves accessible to pollinators. Bears know when to hibernate and awaken. Birds and whales are aware of when to migrate for feeding or breeding. The human female menstrual cycle is almost perfectly attuned to the lunar cycle. Moreover, women who live together often find themselves on identical cycles; much to the despair of their male roommates. So, if humans, like most living creatures, have an internal clock…where do we keep it?

Nearly every cell in the human body operates on its own independent clock system. However, the “master internal” clock mechanism is found in the suprachiasmatic nucleus (SCN); a cluster of about 10,000 brain cells located at the base of our brains in the hypothalamus, close to where the two main nerves from the eyes intersect. These optic nerves allow the SCN to receive external cues from our environment. Moreover, its presence at the base of the brain permits an internal doorway through which it can secrete neuro-hormones that control brain and bodily functions.

The primary function of the SCN is to control about 50 of our circadian (Latin for “about the day”) functions; such as blood pressure and digestive enzymes, as well as fertility and sleep/wake cycles. Our SCN-driven internal clock actually runs a bit longer than the standard 24-hour day. So, how do we keep from becoming ever-more out of synch? Well, our SCN is not quite as accurate as an atomic clock and it resets itself far more often than would be required for a standard timepiece. The SCN knows when to adjust based on zeitgeber (German for “time giver”) cues which come from our natural environment. Each day, these environmental cues, such as the waning of light, prompt our internal clocks to reset each day in order to maintain harmony. The most important time giver for people and animals is light. Light passes directly through our eyes and along the optic nerves to the SCN. During sleep, the presence of light signals the SCN to inhibit the production of melatonin (synthesized from the amino acid tryptophan) which is the hormone that makes you sleepy. Melatonin is produced in the pineal gland which many philosophers believe to be the seat of the human soul or “third eye.” When it gets dark, melatonin production increases, making you tired again; just like Thanksgiving turkey.

Ever wonder why it is so hard to work night shifts? Research conducted at Harvard by Charles Czeisler concluded that this internal clock can be artificially manipulated. During a sleep study, he realized that his participants were operating on a 25-hour per day internal cycle. He discovered that the windowless lab environment was to blame. The researchers had simply turned on the lights when participants awoke and turned them off when they felt sleepy. This artificial sun added an entire hour to the participants’ sleep/wake cycle because the lab lights did not wax and wane as the sun naturally does. After adjusting the lights accordingly, he affirmed that the subjects reverted back to a 24-hour and 11-minute cycle.

Anyone who has ever pulled an all-nighter or taken an international flight is aware of the physiological and psychological effects that occur when your internal clock become out of sync with external ones. During daylight savings, most Americans set their clocks forward one hour in the spring. The result of this is equivalent to each one of them moving one time zone to the east. Subsequently, car accidents increase by 10% the day after clocks are set forward and decrease by a smaller factor the day after clocks are set back to standard time. To combat such issues, human factors engineers have discovered that “cockpit napping” can literally save the lives of airline passengers. Short 20-minute naps by pilots can increase alertness by 50% and performance by 34%. However, the FAA has decided that it is best that only one pilot nap at any given time after one incident wherein a flight bound for Los Angeles continued traveling several hundred miles over the ocean before one of the pilots woke up.  

Seasonal affective disorder (SAD), which is common in those living above 30 degrees latitude, occurs when winter light is short, dim, and far too weak to adequately reset peoples’ internal clocks. Therein, the external signals which are necessary to direct sleep-wake cycles are nonexistent. Consequently, those who suffer from SAD report significant lethargy, depression, and utter loss of interest in most activities which they usually enjoy. In the absence of external causes of stress, these people often have no idea why they feel as they do. Fortunately, the treatment is rather low-tech; sitting in front of a specially-designed light box for 30 minutes each morning after waking. Such intense light provides the necessary external cue to the SCN and effectively resets the internal biological clock, wholly curing the negative symptoms.

In evolutionary terms, the pre-frontal cortex (PFC) is a relatively new addition to the human brain. Its mission is to perform executive functions such as identify goals, predict consequences, delay gratification, and conduct cost-benefit analyses. Essentially, it steers us from temptation and permits us to avoid embarrassing social situations; things that most lower animals and earlier humans need not worry about. 

Undoubtedly, all that planning can have unintended consequences which manifest into stress, anxiety and depression. In 1949, a Nobel Prize in medicine was awarded to Antonio Caetano de Abreu Friere Egas Moniz (yes that is one name). He had developed a radical procedure for treating disabling anxiety disorders and even schizophrenia. Through a process which is, in hindsight, utterly barbaric, he employed a tool similar to an ice pick and effectively destroyed the participant’s pre-frontal cortex. Once completed, the subject experienced a dramatic reduction in stress and anxiety as well as other more profound personality changes. Of course, knowing what we know now, not all of these changes were for the better. While the subjects were no longer anxious, they also became apathetic, lethargic and, in some cases, utterly indifferent to doing or accomplishing anything. Their excessive worry about life was replaced by an inability to enjoy it altogether. Unfortunately, Nobel Prizes cannot be un-awarded.

Approximately 40,000 such lobotomies were conducted in the United States before medications arose as the treatment of choice; which is what most anti-depressants and similar drugs are now used for. Basically, physical and chemical lobotomies wholly eliminate the possibility of having a future time perspective. That is how these modern medications work; you feel happy in the present because you forget the negative aspects of your past and cannot worry about the future. Basically, you are artificially forced to enjoy your plight, but cannot motivate yourself to better your situation. Such is why drugs like Prozac and Thorazine increase suicidal ideation even though you may feel happy in the moment.

Zimbardo, P. & Boyd, J. (2008). The Time Paradox. New York, NY: Simon & Shcuster, Inc.