According to the researchers, adolescents diagnosed with major depressive disorder (MDD) tend to have a small hippocampus, an area of the brain associated with motivation, emotion, and memory formation. Studies elsewhere have shown a connection between loss of hippocampal volume and conditions such as post-traumatic stress disorder (PTSD).
Study authors, Frank MacMaster and Vivek Kusumakar, from Dalhousie University and the National Research Council of Canada looked at 34 adolescents between 13 and 18, half of whom had been diagnosed with MDD. They measured each volunteer's hippocampus size using magnetic resonance imaging (MRI) and found that the hippocampus of patients with MDD averaged 17% smaller than those without MDD.
According to the researchers, adolescents diagnosed with major depressive disorder (MDD) tend to have a small hippocampus, an area of the brain associated with motivation, emotion, and memory formation.
The research is important, say MacMaster and Kusumakar, because, "To our knowledge this is the first published report regarding hippocampal volume in youths with early onset depression compared to healthy controls." The report was published in the January 2004 issue of the journal BMC Medicine.
MDD is a severe and quite common illness that strikes both adolescents and adults. By studying younger patients, some of whom had not been treated, the researchers hoped to find differences in brain structure that may cause the disorder, rather than differences that may be side effects of chronic illness or long-term treatment.
Asked by TheDoctor for comment, Dr. Bruce McEwen, Alfred E. Mirsky Professor at Rockefeller University's Harold and Margaret Milliken Hatch Laboratory of Neuroendocrinology and an acknowledged expert in the field, said: "These findings are very provocative, particularly the smaller hippocampal size before start of treatment. Does this reflect some early life history of abuse or neglect or other disruption that would have led to impaired development of the hippocampus?"
"In light of recent PTSD research," McEwen added, "a careful consideration of familial aspects should be considered — a genetic predisposition or an effect of shared environment which should show up in twins or siblings, perhaps. Finally, it will be interesting to see if other areas of the brain, such as the amygdala, are affected."
Mac Master and Kusumakar characterize their conclusions as "preliminary, considering the small sample sizes used," and 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.
Reviewed by: Bruce S. McEwen, Ph.D.