Researchers from Dalhousie University and the National Research Council of Canada studied 34 adolescents between the ages of 13 to 18 years old, half of whom were suffering from major depressive disorder (MDD). Using magnetic resonance imaging (MRI) they scanned each volunteer's brain and measured the volume of their left and right hippocampuses.
The hippocampus of patients with MDD was, on average, 17% smaller than that of controls. The size difference was particularly evident in the left hippocampus, where the average volume was 2.53cm3 in patients with depression and 3.05 cm3 in those without.
The authors, Frank MacMaster and Vivek Kusumakar, write: "To our knowledge this is the first published report regarding hippocampal volume in youths with early onset depression compared to healthy controls."
MDD is a severe, common and debilitating illness that is as common in adolescence as it is in adulthood. By studying younger patients the researchers hoped that they would be able to see differences in brain structure that may cause the disorder, rather than those differences that are a side effect of long-term illness or treatment.
The reduced size of the brain structure was not a side effect of the treatment, as patients who were not yet being treated for MDD also had small left hippocampuses compared to controls. The study also showed that people that had suffered from MDD for longer had larger hippocampuses than the more recently diagnosed patients. This suggests that in studies of adult patients, who are long-term sufferers of MDD, the initial difference in hippocampus size may not show up.
"These conclusions should be considered preliminary, considering the small sample sizes used," write the authors. They plan to carry out experiments that use larger sample sizes to confirm these initial findings. They also plan to look more closely at how the size of the hippocampus varies with the progression of major depressive disorder.
This press release is based on the following article:
Hippocampal volume in early onset depression
Frank P MacMaster and Vivek Kusumakar
BMC Medicine 2004, 2:2
Published 29 January 2004
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