Anatomical and functional correlates in major depressive disorder: the contribution of neuroimaging studies

Several studies suggested the neural networks modulating aspects of emotional behaviour to be implicated in the pathophysiology of mood disorders. These networks involve the medial prefrontal cortex (MPFC) and closely related areas in the medial and caudolateral orbital cortex (medial prefrontal network), amygdala, hippocampus, and ventromedial parts of the basal ganglia, where alterations in grey matter volume and neurophysiological activity are found in cases with recurrent depressive episodes. Such findings hold major implications for models of the neurocircuits that underlie depression. In particular, evidence from lesion analysis studies suggests that MPFC and related limbic and striato-pallido-thalamic structures organize emotional expression. The aim of this paper is to review the contribution of the most relevant studies with single photon emission tomography (SPECT), positron emission tomography (PET) and magnetic resonance imaging (MRI) to the understanding of pathophysiology of major depressive disorder (MDD), with particular focus on the reversibility of functional correlates with treatment.