Uncovering depression's web in the brain

Depression could come down to stronger and weaker connections between various parts of the brain(Credit: University of Warwick)

Depression is a complicated condition affecting an estimated 350 million people worldwide, according to the World Health Association. While some depressive conditions can be caused by life events, it is increasingly becoming clear that many forms of the condition are caused by either chemical imbalances, brain abnormalities or connections between neurons in the brain. A new study out of the University of Warwick in the UK and Fudan University in China found out just how the latter condition can cause our grey matter to deliver dark days.

The study looked at 909 people in China who had their brains scanned with a high-precision MRI. Four hundred twenty-one of them had major depressive disorder, while 488 were non-depressed control subjects. During the scans, the researchers concerned themselves with the connections stemming from the medial and lateral orbitofrontal cortexes, two of the brain regions implicated in depression.

They found that in depressed individuals, some connections from this region were strengthened, while others were weakened.

Specifically, a circuit tying the reward section of the medial orbitofrontal cortex to sections of the brain linked to memory was found to be weakened. This could lead depressed individuals to have trouble appreciating reward-related incidences and to also have trouble remembering positive experiences. Significantly, the circuit in which the medial orbitofrontal cortex was linked to non-reward and punishing events was not weakened in depressed participants. In other words, they had no problem recognizing and remembering negative events.

The researchers also discovered that a different neuronal circuit was strengthened in depressed people.

This one tied the lateral orbitofrontal cortex to the precuneus (a part of the brain involved in the sense of self), the angular gyrus (a language center), and the temporal visual cortex (a brain region involved in processing visual information). The researchers believe these stronger connections are what lead depressed people to have a negative opinion of themselves or low self esteem. Interestingly, when patients took anti-depressant medications the circuit between these brain regions was weakened.

The researchers believe their discovery could lead to better understanding depression and treating it more effectively.

"More than one in ten people in their lifetime suffer from depression, a disease which is so common in modern society and we can even find the remains of Prozac in the tap water in London," said Jianfeng Feng from Warwick who was involved with the study. "Our finding, with the combination of big data we collected around the world and our novel methods, enables us to locate the roots of depression which should open up new avenues for better therapeutic treatments in the near future for this horrible disease."

The work of Feng and his team has been published in the neurology journal, Brain.

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