Light therapy for SAD not the placebo effect 

Sufferers from SAD who have used light therapy successfully will have little doubt that it is the light that is causing the improvement in their condition. However, they can now point sceptics to new research from Tel Aviv and Minnesota which has shown that light also works in animal models.

Up till now most research on the mechanisms of seasonal affective disorders was carried out on mice and rats but this has been problematic as mice are nocturnal creatures so their reaction to light deprivation is entirely different from that of humans who are diurnal. However, the researchers have now discovered that the Israeli Fat Sand Rat (Psammomys obesus) has a similar reaction to light as humans.

To test the theory, Professor Kronfeld-Schor Schor of Tel Aviv University's Department of Zoology and her fellow exposed one group of sand rats to long hours of light similar to that of the summer season, and the other to shorter hours of the winter length daylight. In several tests, the sand rats of the second group behaved in ways similar to depressed humans, exhibiting despair, reduced social interactions and increased anxiety.

Once the researchers established that Fat Sand Rats and humans had a similar reaction to light, the team explored whether common medications or other SAD therapies would be as effective in their rat population. These studies included a variety of medications commonly used to treat the disorder in humans, as well as a program of exposing the depressed sand rats to brighter light for one hour every morning or evening.

The results surprised the researchers, although they might not have surprised SAD sufferers. The medications were effective in treating the sand rats' depression, but even more effective was the daily exposure to bright light in the mornings, a common treatment for human SAD.
"Humans have been using this treatment for a long time," Professor Kronfeld-Schor Schor explained, "but many of us thought that a large part of its success was based on the placebo effect. For the first time, we've found it to be effective in animals as well, which weakens the possibility of the placebo effect."

Tal Ashkenazy, Haim Einat, Noga Kronfeld-Schor. We are in the dark here: induction of depression- and anxiety-like behaviours in the diurnal fat sand rat, by short daylight or melatonin injections. The International Journal of Neuropsychopharmacology, 2008; 12 (01): 83

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First Published in November 2010

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