In older adults with depression, the brain’s most important memory structure is often reduced in size. This structure, known as the hippocampus, is also smaller in the brain of patients with Alzheimer’s. Furthermore, the onset of Alzheimer’s often comes with symptoms of depression as well. That’s why doctors and researchers have thus far been assuming that the two are linked. Contrary to expectations, however, this assumption turns out to be false.

Does a smaller hippocampus indicate a link between late-life depression and the onset of Alzheimer’s? Professor Mathieu Vandenbulcke and his multidisciplinary team set out to answer this question. The researchers measured the patients’ brain volume with an MRI. Then, with a nuclear brain scan, they looked for a protein linked to the onset of Alzheimer’s.

As expected, the scans showed a smaller hippocampus. More importantly, the researchers also discovered that the reduction of the hippocampal volume was not associated with elevated levels of  the protein that causes Alzheimer’s. This counters the common belief that there is a link between the two conditions.

“A shrunken hippocampus is Alzheimer’s main imprint on our brain,” explains Professor Vandenbulcke. “The onset of the disease often comes with symptoms of depression as well. Therefore, the assumption was that older adults with depression would go on to develop Alzheimer’s disease. Our findings show that this assumption is false.”

“There has to be another explanation for the smaller hippocampus in patients with late-life depression,” Vandenbulcke continues. “Maybe these patients already had a smaller hippocampus to begin with? Or maybe the impact of stress on the brain plays a major role in all of this? We simply don’t know. Unravelling the connection between the ageing of our brain and our psychological functioning is one of today’s major challenges for neuroscientists.”

Click here to read the study in American Journal of Psychiatry

by Tine Danschutter
translated by Katrien Bollen

Source: KU Leuven