Stress experienced in early childhood causes a permanent molecular imprint on the brain that can cause insomnia and depression later in life, according to the doctoral thesis of Olena Santangeli at the University of Helsinki.
Santangeli studies the mechanisms of sleep and depression on a molecular level. Her study involved an experiment where laboratory rats were mildly traumatised by having their mothers switched in a test environment. Santangeli's model shows strong similarities in the stressful experiences of humans who have grown up in difficult life situations.
Research head and dissertation supervisor Tarja Stenberg says that humans and other animals share many mechanisms of sleep.
"The basic functions are the same among all species of animal that we know of," she says.
The study measured the levels of a regulating chemical called adenosine, as well as the frequency of REM sleep, during which the sleeper's eyes move rapidly and the cortex is active, leading to dreams.
Although the reasons for the dream phase are unclear, about one fifth of most sleep is REM sleep. But depressed individuals experience it more often and for longer.
"We noticed that early life stress can lead to increased REM cycles, which is a typical change in sleep patterns found in sufferers of depression," Santangeli says. "It's like a scar in the brain. People who have it can have a harder time with challenges as adults, and become depressed."
Hand in hand with insomnia
The dissertation also studied sleep disorders among teenage boys with early signs of depression. Santangeli says she found out that depressed boys experienced less slow-wave sleep, which correlates with the severity of the diagnosis. Slow-wave sleep is the deepest part of a sleep cycle.
"This is an important discovery, because it shows that disrupted sleep is one of the first symptoms of developing depression," says Santangeli. "Doctors could ask insomniacs at the clinic whether they have any symptoms of depression, which could lead to early prevention of mental disorders."
The way we sleep as adults is a very sensitive indicator of how our central nervous system has been stressed in early childhood.
Range of reasons
So should insomniacs assume they've experienced early life trauma?
"It's possible of course, but there are so many reasons for sleep trouble that the first thing to look at should be one's surroundings," Stenberg says. "What stress factors are involved, whether it's the wrong partner, the wrong job, or something else. If there's nothing in the now that could explain it, then it might be time to think of other root causes."
One thing Santangeli can say for sure is that children with early life stress arising from parental negligence or abuse are more likely to stress out as adults than children with a safe, loving upbringing.