"This is very clear evidence that the 'clock' in the brain is disrupted in depression," Akil said.
That makes sense, since doctors and researchers have long seen signs of a disturbed circadian rhythm in people with depression, said Eva Redei, a professor of psychiatry at the Northwestern University Feinberg School of Medicine in Chicago.
Those signs, Redei said, include sleep problems -- like sleeping too much or too little -- and abnormal activity in the "stress hormone" cortisol, which follows a daily rhythm. There also is a form of depression known as seasonal affective disorder (SAD) in which people suffer symptoms during the short days of winter but feel better during the sunnier seasons.
Experts do not know the precise cause of SAD, but Redei said it involves problems with the circadian rhythms.
This study, Redei said, "very nicely proves" that a disruption in the brain's daily gene activity exists in depression.
Both she and Akil said a big unknown is whether out-of-sync brain genes are an initial cause of depression or a result of the disorder.
Either way, Akil said she thinks the out-of-sync genes would feed people's symptoms. Think about how bad you feel, she said, when the body's normal rhythms are thrown off due to jet lag.
In the future, Akil said, the findings might help lead to new "biomarkers" for diagnosing depression or tracking how well the disorder is responding to treatment. But first, Redei said, researchers would have to see if the altered gene activity in the brain correlates with something doctors can actually measure -- such as something they can see in brain imaging or something they can analyze in the blood.
The findings might also help identify new "molecular targets" for depression treatment, Akil said.
Right now, antidepressant drugs target certain chemicals in the brain believed to contribute to depression -- most famously, the mood-regulating chemical
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