A research team at Yeouido St. Mary's Hospital has identified the mechanisms of depression and Alzheimer's disease (AD)-induced dementia for the first time in the world.

"Many studies have shown that severe depression in older adults can lead to AD-induced dementia," the hospital said. "However, the exact mechanism of how depression increases the risk of AD and develops into dementia remained unclear."

To resolve this issue, the team, led by Professors Im Hyun-gook and Wang Sung-min of the Department of Mental Health, performed F-18 flormethamol brain positron emission tomography (PET) and functional magnetic resonance imaging (MRI) tests on people aged 60 years or older who visited outpatient departments of the hospital's Brain Health Center from 2017 to 2019.

The research team divided 235 patients into a depression group (118 patients) and a non-depression group (117 patients).

Researchers then analyzed beta-amyloid protein accumulation, brain functional connectivity, and association with depression. Compared to the non-depression group, the functional connection of the anterior subgenual anterior cingulate cortex of the default mode network, one of the important cerebral networks, increased in the depressed group, while the functional connection of the posterior cingulate cortex decreased.

They also confirmed that higher beta-amyloid protein accumulation increased the anterior connectivity of the default mode network while reducing the posterior connectivity.

The default mode network anterior and posterior separation was more severe in the depressed group.

"As the anterior connectivity increased, the symptoms of depression became more severe, and as the posterior connectivity decreased, the memory deteriorated," the team said.

For the first time in the world, the research team discovered that the accumulation of beta-amyloid protein, known as a major risk factor for Alzheimer's disease, is not a direct factor in the development of depression but causes depression by increasing the anterior activity of the default mode network.

It observed that when the separation between the anterior and posterior of the default mode network becomes severe, the network connection interval becomes impossible to restore to the previous state and accelerates AD-led dementia.

"We expect this study to be helpful in the diagnosis and treatment of dementia as hospitals will understand more clearly the relationship between elderly depression and AD," Professor Wang said.

Professor Im also said, "For older adults who show signs of depression, early diagnosis and treatment are important to prevent dementia."

The published The study results were published in the June edition of Neuropsychopharmacology.