Depression and Our Internal Clocks

Severe depression has long been linked with disruptions in daily cycles -- depressed people are more likely than others to sleep at odd hours, sleep to little or too much, suffer from insomnia, wake not knowing what time it is, and so on.

Now a study of the brains of recently deceased people, 34 with clinical depression and 55 without, showed differences in activity at the genetic level:

After determining how long after sunrise each person’s death was, the team looked at what genes were turned on in six brain regions, gathering a total of 12,000 records of gene activity. Among nondepressed people, patterns were pretty predictable. One gene’s activity, for example, consistently peaked at sunrise, another's at midday, Li says. But in the depressed brains, gene activity seemed uncoupled from time of day. Their patterns of activity also weren’t as predictable.

Nobody knows which way the causality flows: maybe depressed people have trouble keeping on schedule, or maybe a disrupted schedule contributes to depression. But the connection is real.