Major depressive disorder (MDD) is a heterogeneous disease that affects one out of five individuals in their lifetime and is the leading cause of disability worldwide. The symptoms of MDD are associated with structural and neurochemical deficits in the corticolimbic brain regions. The behavioral symptoms of depression are extensive, covering emotional, motivational, cognitive, and physiological domains, and include anhedonia, aberrant reward-associated perception, and memory alterations. Presently, MDD is considered a multifactorial disease with various causes and triggers such as genetic susceptibility, stress, and other pathological processes such as inflammation.