Bring on the light: nature's mood-changing drug

By Gary Raham
Nature Writer and Illustrator

I love what autumn light does lancing through aspen leaves, showing off their colors and sharpening every leaf edge to knife-blade clarity.

But the light just doesn't last long enough. My energy seems to fade right along with the shortening day length--and for good reason. Light is nature's drug-of-choice for entraining creatures to daily and seasonal rhythms. Light does much more than keep us from tripping over our house pets and furniture. It changes our moods and activity cycles to match the seasons. Sometimes we tend to ignore what we know about this feature of light to meet the rigid needs of work and family, and sometimes our personal brain chemistry suffers from pesky genetic malfunctions--some of which can be helped with something called light therapy.

Those of you old enough to remember the TV show "Northern Exposure" (set in Alaska) may recall the character that ran around wearing a visor with artificial lights underneath. Otherwise, the Alaskan nights depressed him right into lethargy. The set-up was comic on the show, but light therapy does work for people that suffer from SAD, seasonal affective disorder. Although all the reasons why these treatments are effective are still a bit fuzzy, scientists have made progress unraveling light's nonvisual role in changing our brain chemistry to suit the season.

Some of the light that enters our eyes travels to a brain region called the hypothalamus. The hypothalamus manages lots of key bodily activities and functions by dispensing various hormones that regulate metabolism, reproduction, memory and emotion. It also regulates core body temperature. So, anything bouncing around in the hypothalamus can shake up your body politics pretty effectively. Light has profound impacts on our biological clocks--chemical systems that tell our bodies what time of day and what time of year it is. The colors (wavelengths), intensity, timing and duration of light we encounter can affect the impact of light on these clocks.

For example, light tells the pineal gland (part of the hypothalamus) to keep the levels of a chemical called melatonin low during the day (for humans and other mammals that are typically active during the day). At night, melatonin levels rise. However, exposure to sufficient light at night can significantly decrease the levels of this chemical and interfere with sleep. Shift workers, who are on the job different parts of the day and night on a rotating basis, can sometimes suffer from disrupted daily (circadian) rhythms. This can turn from inconvenient to dangerous if work involves things like driving, using heavy equipment or telling planes where to land. Similarly, if we travel far enough, the light pouring into our eyes gives our brains the impression that we are in a different part of the daily cycle than we are, and we suffer jet lag.

But light may impact behavior in ways not related to circadian or seasonal rhythms. A study on rats reported in 1998 showed that sleep/wake patterns could be changed by changes in lighting conditions and that a different part of the brain was involved: two interconnected midbrain structures called the superior colliculus and the pretectum. This and ongoing research may ultimately help explain how fairly modest light exposure can improve the moods of people who suffer from some form of depression during the winter months.

Many of us suffer from the winter doldrums. We feel a bit down, want to eat a lot of chocolate, growl at our spouse, and may feel like hibernating with Yogi or some other warm bear. Those suffering from SAD, however, experience these emotions and cravings to such a degree that they literally may not be able to function.

A series of scientific studies demonstrated in the '80s and '90s that exposure to light of certain wavelengths and intensities can dramatically improve symptoms in such individuals in as short a time as a week. Regular therapy --which sometimes includes visors like the character on "Northern Exposure" wore--can allow these individuals to function during long winters. The Society for Light Treatment and Biological Rhythms, a nonprofit international organization formed in 1988, dedicates its activities to "fostering research, professional development and clinical applications in the fields of light therapy and biological rhythms." Its web site at www.sltbr.org provides information and links to various corporate members who provide therapeutic services.

Architects are beginning to design workplaces, schools, and other buildings to accommodate what we know about light's impact on behavior. New schools, like the one going up in Wellington, for example, are designed to provide much more natural light that should improve learning (and teaching) environments for all concerned. Hopefully, civil engineers will continue to incorporate what science uncovers about light's amazing liaison with our brain's chemistry.

The biological basis of light's impact on rhythms and behavior is an ancient one. Much current work is done on fruit flies because they reproduce quickly, make docile subjects that take up little lab space, and they have a set of what geneticists call the F-box genes implicated in light mediated rhythms shared by both arthropods and clever vertebrates like us. Even cyanobacteria, otherwise known as pond scum, have internal clocks that keep their behaviors in tune with the sun.

Light is more than just a pretty rainbow of wavelengths to admire. It's also a powerful tool to make us feel and function at our best through all the days and seasons of our life.