I’m not a huge winter fan. I don’t like the cold, and I don’t like just a few measly hours of sunlight. That’s probably why I live in the southwest. But despite that, I still find myself feeling more lethargic in the winter than in the summer. It turns out this is pretty common. More severe cases, involving bouts of depression, is actually diagnosable. It’s called Seasonal Affective Disorder (appropriately shortened to SAD). SAD is a mood disorder in which individuals have normal mental wellbeing during most of the year, but then have more “depressive” symptoms in the winter and during times of short-light days.

One culprit of SAD is melatonin, a hormone secreted by the pineal gland, which is located in the brain. It helps control your sleep and wake cycles, like the biological clock and circadian rhythms. It affects your mood and energy levels, and the amount of melatonin produced depends on how much light your body is receiving. In wintertime, melatonin levels are produced usually later in the day than during the summertime. The change in light levels, and thus melatonin levels, can lead to these symptoms of SAD. People, and hamsters, with SAD may be under sensitive to light, unable to perceive artificial light as a longer day during the wintertime.

An interesting fact about SAD: it’s not just human-specific; it actually happens to hamsters (and likely other animals), too. I was curious about this because how do you really know if or when a hamster is depressed? After some research, I found that there were a series of experiments done on hamsters back in 2005 at Ohio State University.

Hamsters are thought to be anxious or depressed if they spend more time near the walls of their cages instead of staying in the center; if they forgo sugar water; and if they float in water. Apparently, hamsters don’t sink, they float. But if they swim and are active in the water, it’s a sign of being content, as opposed to just floating.

In this study, researchers housed both male and female Siberian hamsters in containers that were created to mimic long summer days or short winter days. These were simulated with 16 hours of light and eight hours of light, respectively. After 10 weeks in these containers, hamsters were given the “float or sink test” and then had their brains removed 48 hours later. They were tested for anxiety and depression, seen by hippocampal and cell body size. Researchers said they found their results showed a link between the amount of light hamsters received and their attitudes. The less light hamsters received the more anxious or depressed they were perceived to be. Also, hamsters born in wintertime tended to be more susceptible to SAD than those hamsters born in summertime.

While it is flawed to conclude the same for humans, based on the results of a Siberian hamster, it makes me wonder if there isn’t something to the old adage, “go south for the winter,” where the days are lighter longer. Let me see if I can find that human study somewhere…

Source: Workman, Joanna L. “Photoperiodic Regulation of Affective Responses and Hippocampal Cell Morphology in Siberian Hamsters” 2005

Image of Siberian hamster from www.asknature.org