[Neurobiology of neuronal circuits invoved in depression]

Many authors consider the most important step in understanding depression is to identify the neural systems responsible for this disease, thereby allowing treatment to be guided towards specific targets. Some of the neural networks that are involved in depression are already known thanks to molecular, neuroimaging, pathological and functional studies. Specific increases or decreases in certain activities, certain lesions and biochemical alterations and receptors as well as plasticity processes that are involved in depression-associated neural networks have been identified. These networks include cortical and subcortical structures that modulate cognitive and emotional aspects of behavior and the neural systems related to decision making and energy-vitality in thought and action. This article reviews and presents the best-studied networks and the alterations that are most likely to be involved in the pathophysiology of depression that can be summarized in the following points: 1) The medial prefrontal network is a nodal link of the neural network involved in the major (MDD) and bipolar (BD) depressive disorders, here the anatomical connections in the macaque monkey of one of the most distinctive components of this network: the medial orbitofrontal cortex are reviewed based on the findings of our group. 2) The neuroimaging and pathological findings in terms of size, composition and functionality of brain structures, specially this network, in patients with MDD and BD are summarized. 3) The neural circuit involved in the MDD and BD is proposed and discussed. 4) The results of the first well regulated and controlled study on deep brain stimulation for treatment-resistant MDD and BD patients are presented.