State dependent posterior hippocampal volume increases in patients with major depressive disorder.

Background: The hippocampal formation has been implicated in etiology and therapy response in major depressive disorder (MDD). However, prospective longitudinal studies investigating volumes in hippocampal subregions and their association with clinical findings are still lacking.

Methods: Global and regional hippocampal volumes and neuropsychological performance were assessed longitudinally in 15 young patients with unipolar early onset MDD who responded to therapy and 13 matched healthy control subjects.

Results: Although volumes at baseline did not differ between groups, patients with MDD showed significant posterior hippocampal volume increases during the treatment course (mean observation period 161.4 ± 58.6 days). Posterior hippocampal volume increases were seen in every single patient. The detected posterior hippocampal volume increases were significantly correlated with the number of solved problems in a planning task at baseline.

Limitations: The study is limited by the small sample size. Moreover, future studies should include patients who do not respond to antidepressant treatment.

Conclusion: Patients with MDD showed selective increases in posterior hippocampal volumes which were not correlated to the degree of functional restitution. However, posterior hippocampal volume increases might constitute a surrogate parameter of neuroplasticity taking place during antidepressant therapy which might be predicted by executive functioning at baseline.