Lorenzetti V, b, Allen NB, Whittle S, Yücel M.
Melbourne Neuropsychiatry Centre, Department of Psychiatry, The University of Melbourne and Melbourne Health, Australia; ORYGEN Youth Health Research Centre, The University of Melbourne, VIC, Australia; Department of Psychology, The University of Melbourne, VIC, Australia
Background: Major Depressive Disorder is associated with amygdala volumetric alterations. To date, it is still unclear (I) whether amygdala volumetric alterations constitute a state or a trait marker of MDD; (II) what influences the direction of amygdala morphometric changes (i.e., enlargement versus shrinkage); and (III) what the role of laterality is in amygdala volumetric alterations in MDD.
Methods: We investigated amygdala volume in a sample of 31 currently depressed patients (cMDD), 31 healthy subjects with a previous diagnosis of MDD (rMDD) and 31 healthy controls, using images obtained from a 1.5 Tesla MRI scanner. The groups were matched for age and gender.
Results: We found that left amygdala volumes of rMDD subjects were significantly larger as compared to healthy controls, and tended to be larger when compared to cMDD subjects. There was no difference in left amygdala volumes between cMDD patients and healthy controls. Right amygdala volumes did not differ between groups.
Conclusions: Given that amygdala alterations were present only in remitted patients, we suggest that such alterations appear to be a state marker of MDD. Further, we found evidence of a lateralization effect, with changes in the left hemisphere only. Left amygdala enlargement in the rMDD group may represent a neurobiological marker of vulnerability to relapse, or may reflect recovery from MDD, whereby volumetric changes have resulted from stress associated with the last depressive episode.
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Epidemiological studies describing population characteristics which collect data at one point in time and then consider relationships between observed characteristics.. Because they don't look at time trends they cannot establish causes.