Research has long associated poor sleep with an increased risk of depression, but scientists have just identified the neural mechanism responsible for this link – a discovery that could lead to better treatments in the future.
Researchers found a strong connection between the dorsolateral prefrontal cortex (responsible for short-term memory), the precuneus (linked with ideas of the self) and the lateral orbitofrontal cortex (associated with negative emotions).
An analysis of the records of 9,735 people living with depressive problems found that there was increased activity between these brain regions in people who also reported disrupted sleep patterns, and that's a crucial discovery in our understanding of these conditions.
"The relation between depression and sleep has been observed more than one hundred years, and now we have identified the neural mechanisms of how they are connected for the first time," says one of the team, Jianfeng Feng from the University of Warwick in the UK.
"These findings provide a neural basis for understanding how depression relates to poor sleep quality, and this in turn has implications for treatment of depression and improvement of sleep quality because of the brain areas identified."
The researchers have hypothesised that this brain activity might be a sign of negative emotions bouncing around in the mind – partly explaining why problems with sleep and problems with depression often go together.
What we know so far is that people who have issues with depression are more likely to have insomnia or find it hard to get to sleep. From the other side, people with insomnia also have a higher risk of depression and anxiety.
While this particular study found strong neural connections in the association of depressive problems with poor sleep quality, rather than the other way around, in general the effects can work both ways.
Getting to the bottom of exactly what's going on will require more research, but one of the more promising avenues to explore is the role of the lateral orbitofrontal cortex.
Specifically targeting this part of the brain with treatments, the study authors say, could lead to some major progress being made.
With depression thought to affect more than 300 million people worldwide, the more we can understand about how it works through the brain, the quicker we can figure out ways of reducing its harmful effects – and targeting this newly identified set of connections in the brain could lead to fresh progress.
In this particular case, the researchers say, scientists might be able to discover ways of helping those experiencing problems with depression to get a better night's rest.
What isn't helping at all is the increasing pace of modern-day living, meaning more and more of us are going without the sleep we need – which again leads to a whole host of mental and physical health problems.
"In today's world, poor sleep and sleep deprivation have become common problem affecting more than a third of the world's population due to the longer work hours and commuting times, later night activity, and increased dependency on electronics," says Feng.
The research has been published in JAMA Psychiatry.