A new study shows the reason some adolescents experience Depression could be abnormal brain structure. The study published in BioMed Central Medicine states depressed teenagers tend to have a smaller hippocampus - the part of the brain responsible for memory, learning, emotion and motivation.

Researchers from Dalhousie University and the National Research Council of Canada sampled nearly 30 adolescents between ages 13 to 18, half of who had been diagnosed with major depressive disorder.

Magnetic resonance imaging was performed to measure the volume of each teen’s left and right hippocampus. The results indicated that the hippocampus of patients with Depression was, on average, 17 percent smaller than those without mental illness.

The study also found people suffering from Depression for a longer time had larger hippocampuses. This implies long-term Depression patients might not show an initial difference in hippocampus measurement.

Researchers chose to study adolescents to get a more accurate measure of the link between Depression and brain size. Choosing to study adult patients may have introduced side effects of long-term illnesses or treatment.

The authors write, “These conclusions should be considered preliminary, considering the small sample sizes used.” Researchers plan future experiments with larger numbers of individuals and to study the size of the hippocampus as Depression progresses.

Disorders involving the hippocampus are also associated with Alzheimer’s disease and epilepsy.