Reduced hippocampal volume observed in currently but not previously depressed older adults

A study of older adults has found that depression is associated with shrinkage of the hippocampus. But the findings, which were published in the Journal of Psychiatric Research, provide preliminary evidence that the hippocampus can recover from depression-related reductions in volume.

“We focused on the hippocampus because it is one of the main cerebral structures studied in depression and hippocampal volume reductions have been repeatedly reported in neuroimaging studies of depressed patients. However, hippocampal volume reduction in late life depression may also be linked to neurodegenerative disorders,” said study author Raffaella Calati of the University of Montpellier.

“Hence, we decided to investigate differences between currently depressed individuals, persons with past major depressive episode, and healthy controls, excluding patients with dementia.”

The researchers examined data from a study of psychiatric disorders in 1,863 older adults (aged 65 and over), who had undergone clinical, biological and neuroimaging assessment at the Gui de Chauliac Neurology Hospital of Montpellier.

By analyzing MRI brain scans, Calati and her colleagues observed hippocampal volume reduction in currently depressed participants compared to the healthy control group. But they found no significant difference between those with a history of past, but not current, depression and the healthy controls.

“When we compared the three groups, we found left posterior hippocampal volume reduction in currently depressed individuals when compared to healthy subjects. This reduction was not present when we compared past depressed subjects to healthy controls,” Calati explained.

“We hypothesized that this result could be linked to brain neuroplasticity (i.e., the modification and reorganization of neural circuits in response to external or internal stimuli). So the human brain, and the hippocampus in particular, could have the capacity to ‘recover’ and restore its original basal rate of neurogenesis, thanks to antidepressant treatment or endogenous changes.”

The study has some limitations.

“Brain neuroplasticity could be only hypothesized in our study because we were able to measure the hippocampal volume at one time point only. To test this hypothesis longitudinal studies with more than one measure of brain structures are needed,” Calati said.

“Even if we should be cautious in the interpretation of results, we have to underline that we used a highly conservative approach and the analysed sample was large.”

The study, “Smaller hippocampal volume in current but not in past depression in comparison to healthy controls: Minor evidence from an older adults sample“, was authored by Ismaïl Bensassi, Jorge Lopez-Castroman, Jerome J. Maller, Chantal Meslin, Marilyn Wyart, Karen Ritchie, Philippe Courtet, Sylvaine Artero, and Raffaella Calati.