Major depression and sleep problems are fundamentally interlinked. A new study from a team of international researchers has now found a unique neurological mechanism that underlies this association, offering new insights into how we can understand and hopefully treat major depression.

"The relation between depression and sleep has been observed [for] more than one hundred years, and now we have identified the neural mechanisms of how they are connected for the first time," explains Jianfeng Feng, a researcher on the project from the University of Warwick.

In total, the researchers examined data from nearly 10,000 people looking to find a neurological pattern that corresponded with both depression and disrupted sleep. The results revealed that those suffering from depression and bad sleep displayed unusually increased connectivity between three different brain regions: the dorsolateral prefrontal cortex, the precuneus, and the lateral orbitofrontal cortex.

"The understanding that we develop here is consistent with areas of the brain involved in short-term memory (the dorsolateral prefrontal cortex), the self (precuneus), and negative emotion (the lateral orbitofrontal cortex) being highly connected in depression, and that this results in increased ruminating thoughts which are at least part of the mechanism that impairs sleep quality," says Jianfeng Feng.

The concluding hypothesis is that it is the increased activity between these three brain regions that explains at least part of the neural mechanism behind disrupted sleep as a symptom of depression. The researchers suggest this specific neural activity is responsible for that sensation where excessive negative thoughts bounce around a person's head as they try to fall asleep. It's this action that can lead to poor sleep in association with depression.

One of the novel observations in the research is the role of the lateral orbitofrontal cortex in both depression and sleep disruption. It is only recently that this brain region has been explored for its part in depression and the researchers suggest it could be a very effective target for future treatments. It is also suggested that while transcranial magnetic stimulation is a growing area of research as a novel depression treatment, targeting the lateral orbitofrontal cortex with this technique could be a beneficial future treatment.

The new study was published in the journal JAMA Psychiatry.