Even before the sadness settles in, the brains of people with a family history of depression look different and work differently than those of people with no depressive family history.

In a new study, published in the Proceedings of the National Academy of Sciences, researchers from Columbia University provide some insight into how — for those with a family history of depression — the illness progresses from symptoms that are barely perceptible to a disabling mood disorder.

On average, people with a family history of depression appear to have brains that are 28 per cent thinner in the right cortex — the outermost layer of the brain — than those with no known family history of the disease. That cortical thinning, said the researchers, is on a scale similar to that of patients with Alzheimer’s disease or schizophrenia.

“These are really impressive anatomical differences,” said Dr Bradley Peterson, the lead author of the study. The greater the anatomical differences seen in patients, on average, the more severe were their symptoms of intellectual impairment.

But thinning on the right side was associated with cognitive problems only; when thinning began on the left side of the cortex, the hallmark symptoms of depression or anxiety became evident as well.

People who suffer from major depressive disorder are sad, yes. But researchers have long noted that most depressives have a wide range of other cognitive problems: They often have trouble concentrating, fail to pick up on social cues — like facial expressions — that don’t conform with their negative thoughts, and their memories sometimes seem full of holes.

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