Douglas McMahon is fascinated by the circadian rhythms of mice.  He spends hours studying them in his lab at Vanderbilt University.  McMahon and his team have discovered something that may provide clues to why humans born in the winter have an increased risk of mood and psychological disorders.

In a study published Sunday in the journal Nature Neuroscience, McMahon and his colleagues took two groups of newborn mice and controlled their exposure to light.  "We were curious to see if light signals could shape the development of the biological clocks," says McMahon, a professor of Biological Sciences at Vanderbilt in a news release.  "Our biological clocks measure the day length and change our behavior according to the seasons."

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